Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
On 07/17/2012 01:19 AM, Itamar Heim wrote: On 07/09/2012 09:52 PM, Saggi Mizrahi wrote: - Original Message - From: Itamar Heim ih...@redhat.com To: Saggi Mizrahi smizr...@redhat.com Cc: Adam Litke a...@us.ibm.com, vdsm-devel@lists.fedorahosted.org Sent: Monday, July 9, 2012 11:03:43 AM Subject: Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm On 07/09/2012 05:56 PM, Saggi Mizrahi wrote: I don't think AMQP is a good low level supported protocol as it's a very complex protocol to set up and support. Also brokers are known to have their differences in standard implementation which means supporting them all is a mess. It looks like the most accepted route is the libvirt route of having a c library abstracting away client server communication and having more advanced consumers build protocol specific bridges that may have different support standards. On a more personal note, I think brokerless messaging is the way to go in ovirt because, unlike traditional clustering, worker nodes are not interchangeable so direct communication is the way to go, rendering brokers pretty much useless. but brokerless doesn't let multiple consumers which a bus provides? All consumers can connect to the host and *some* events can be broadcasted to all connected clients. The real question is weather you want to depend on AMQP's routing \ message storing Also, if you find it preferable to have a centralized host (single point of failure) to get all events from all hosts for the price of some clients (I assume read only clients) not needing to know the locations of all worker nodes. But IMHO we already have something like that, it's called the ovirt-engine, and it could send aggregated events about the cluster (maybe with some extra enginy data). The question is what does mandating a broker gives us something that an AMQP bridge wouldn't. The only thing I can think of is vdsm can assume unmoderated vdsm to vdsm communication bypassing the engine. This means that VDSM can have some clustered behavior that requires no engine intervention. Further more, the engine can send a request and let the nodes decide who is performing the operation among themselves. Essentially: [ engine ] [ engine ] | | VS | [vdsm][vdsm] [ broker ] | | [vdsm][vdsm] *All links are two way links This has dire consequences on API usability and supportability. So we need to converge on that. There needs to be a good reason why the aforementioned logic code can't sit on a another ovirt specific entity (lets call it ovirt-dynamo) that uses VDSM's supported API but it's own APIs (or more likely messaging algorithms) are unsupported. [engine ] ||| | [ broker ] | ||| | [vdsm]-[dynamo] : [dynamo]-[vdsm] Host A : Host B *All links are two way links 1. we have engine today 'in the path' to the history db. but it makes no sense for engine to be aware of each statistic we want to keep in the history db. same would be for an event/stats correlation service. they don't need to depend on each other for availability/redundancy. 2. we are already looking at quantum integration, which is doing engine to nodes communication via amqp. 3. with somewhat of a forward looking - moving some scheduling logic down to vdsm will probably mean we'll want one of the nodes to listen to statistics and state from the other nodes. to all of these, setting up a bus which allows multiple peer listeners seems more robust I'm still against developing a C level binding for amqp and rest support over a codebase which is in python. rest and amqp allow for both local and remote bindings in any language. C bindings should/could be a parallel implementation, but they seem like an unneeded overhead and complexity in the middle of the codebase. ___ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://fedorahosted.org/mailman/listinfo/vdsm-devel
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
On Thu, Jul 26, 2012 at 11:47:51AM +0300, Itamar Heim wrote: On 07/17/2012 01:19 AM, Itamar Heim wrote: On 07/09/2012 09:52 PM, Saggi Mizrahi wrote: - Original Message - From: Itamar Heim ih...@redhat.com To: Saggi Mizrahi smizr...@redhat.com Cc: Adam Litke a...@us.ibm.com, vdsm-devel@lists.fedorahosted.org Sent: Monday, July 9, 2012 11:03:43 AM Subject: Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm On 07/09/2012 05:56 PM, Saggi Mizrahi wrote: I don't think AMQP is a good low level supported protocol as it's a very complex protocol to set up and support. Also brokers are known to have their differences in standard implementation which means supporting them all is a mess. It looks like the most accepted route is the libvirt route of having a c library abstracting away client server communication and having more advanced consumers build protocol specific bridges that may have different support standards. On a more personal note, I think brokerless messaging is the way to go in ovirt because, unlike traditional clustering, worker nodes are not interchangeable so direct communication is the way to go, rendering brokers pretty much useless. but brokerless doesn't let multiple consumers which a bus provides? All consumers can connect to the host and *some* events can be broadcasted to all connected clients. The real question is weather you want to depend on AMQP's routing \ message storing Also, if you find it preferable to have a centralized host (single point of failure) to get all events from all hosts for the price of some clients (I assume read only clients) not needing to know the locations of all worker nodes. But IMHO we already have something like that, it's called the ovirt-engine, and it could send aggregated events about the cluster (maybe with some extra enginy data). The question is what does mandating a broker gives us something that an AMQP bridge wouldn't. The only thing I can think of is vdsm can assume unmoderated vdsm to vdsm communication bypassing the engine. This means that VDSM can have some clustered behavior that requires no engine intervention. Further more, the engine can send a request and let the nodes decide who is performing the operation among themselves. Essentially: [ engine ] [ engine ] | | VS | [vdsm][vdsm] [ broker ] | | [vdsm][vdsm] *All links are two way links This has dire consequences on API usability and supportability. So we need to converge on that. There needs to be a good reason why the aforementioned logic code can't sit on a another ovirt specific entity (lets call it ovirt-dynamo) that uses VDSM's supported API but it's own APIs (or more likely messaging algorithms) are unsupported. [engine ] ||| | [ broker ] | ||| | [vdsm]-[dynamo] : [dynamo]-[vdsm] Host A : Host B *All links are two way links 1. we have engine today 'in the path' to the history db. but it makes no sense for engine to be aware of each statistic we want to keep in the history db. same would be for an event/stats correlation service. they don't need to depend on each other for availability/redundancy. 2. we are already looking at quantum integration, which is doing engine to nodes communication via amqp. 3. with somewhat of a forward looking - moving some scheduling logic down to vdsm will probably mean we'll want one of the nodes to listen to statistics and state from the other nodes. to all of these, setting up a bus which allows multiple peer listeners seems more robust I'm still against developing a C level binding for amqp and rest support over a codebase which is in python. rest and amqp allow for both local and remote bindings in any language. C bindings should/could be a parallel implementation, but they seem like an unneeded overhead and complexity in the middle of the codebase. Sure, it's probably possible to bind a REST or AMQP API in other languages but I don't think there is an automatic way of doing it. That means having to keep up with maintenance of each and every binding every time the API changes. If we look at libvirt, they will say this is a large source of pain that they have recommended we avoid. For the C/gobject approach, we write a single API schema file. From that, we automatically generate the C API and bindings. Sure, the generation could be a bit complex but much of it will be someone else's codebase (and one that is used by lots of Gnome projects). -- Adam Litke a...@us.ibm.com IBM Linux Technology Center ___ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://fedorahosted.org/mailman/listinfo/vdsm-devel
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
On 07/26/2012 04:33 PM, Adam Litke wrote: On Thu, Jul 26, 2012 at 11:47:51AM +0300, Itamar Heim wrote: On 07/17/2012 01:19 AM, Itamar Heim wrote: On 07/09/2012 09:52 PM, Saggi Mizrahi wrote: - Original Message - From: Itamar Heim ih...@redhat.com To: Saggi Mizrahi smizr...@redhat.com Cc: Adam Litke a...@us.ibm.com, vdsm-devel@lists.fedorahosted.org Sent: Monday, July 9, 2012 11:03:43 AM Subject: Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm On 07/09/2012 05:56 PM, Saggi Mizrahi wrote: I don't think AMQP is a good low level supported protocol as it's a very complex protocol to set up and support. Also brokers are known to have their differences in standard implementation which means supporting them all is a mess. It looks like the most accepted route is the libvirt route of having a c library abstracting away client server communication and having more advanced consumers build protocol specific bridges that may have different support standards. On a more personal note, I think brokerless messaging is the way to go in ovirt because, unlike traditional clustering, worker nodes are not interchangeable so direct communication is the way to go, rendering brokers pretty much useless. but brokerless doesn't let multiple consumers which a bus provides? All consumers can connect to the host and *some* events can be broadcasted to all connected clients. The real question is weather you want to depend on AMQP's routing \ message storing Also, if you find it preferable to have a centralized host (single point of failure) to get all events from all hosts for the price of some clients (I assume read only clients) not needing to know the locations of all worker nodes. But IMHO we already have something like that, it's called the ovirt-engine, and it could send aggregated events about the cluster (maybe with some extra enginy data). The question is what does mandating a broker gives us something that an AMQP bridge wouldn't. The only thing I can think of is vdsm can assume unmoderated vdsm to vdsm communication bypassing the engine. This means that VDSM can have some clustered behavior that requires no engine intervention. Further more, the engine can send a request and let the nodes decide who is performing the operation among themselves. Essentially: [ engine ] [ engine ] | | VS | [vdsm][vdsm] [ broker ] | | [vdsm][vdsm] *All links are two way links This has dire consequences on API usability and supportability. So we need to converge on that. There needs to be a good reason why the aforementioned logic code can't sit on a another ovirt specific entity (lets call it ovirt-dynamo) that uses VDSM's supported API but it's own APIs (or more likely messaging algorithms) are unsupported. [engine ] ||| | [ broker ] | ||| | [vdsm]-[dynamo] : [dynamo]-[vdsm] Host A : Host B *All links are two way links 1. we have engine today 'in the path' to the history db. but it makes no sense for engine to be aware of each statistic we want to keep in the history db. same would be for an event/stats correlation service. they don't need to depend on each other for availability/redundancy. 2. we are already looking at quantum integration, which is doing engine to nodes communication via amqp. 3. with somewhat of a forward looking - moving some scheduling logic down to vdsm will probably mean we'll want one of the nodes to listen to statistics and state from the other nodes. to all of these, setting up a bus which allows multiple peer listeners seems more robust I'm still against developing a C level binding for amqp and rest support over a codebase which is in python. rest and amqp allow for both local and remote bindings in any language. C bindings should/could be a parallel implementation, but they seem like an unneeded overhead and complexity in the middle of the codebase. Sure, it's probably possible to bind a REST or AMQP API in other languages but I don't think there is an automatic way of doing it. That means having to keep up with maintenance of each and every binding every time the API changes. If we look at libvirt, they will say this is a large source of pain that they have recommended we avoid. we'd need this on top of the C api as well - but it would probably be simpler doing it over the python api, rather than the C one. For the C/gobject approach, we write a single API schema file. From that, we automatically generate the C API and bindings. Sure, the generation could be a bit complex but much of it will be someone else's codebase (and one that is used by lots of Gnome projects). that's a critical part of the question for the C api - what is needed for adding a verb / parameter. I'm not against having c bindings. what i don't
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
On 07/09/2012 09:52 PM, Saggi Mizrahi wrote: - Original Message - From: Itamar Heim ih...@redhat.com To: Saggi Mizrahi smizr...@redhat.com Cc: Adam Litke a...@us.ibm.com, vdsm-devel@lists.fedorahosted.org Sent: Monday, July 9, 2012 11:03:43 AM Subject: Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm On 07/09/2012 05:56 PM, Saggi Mizrahi wrote: I don't think AMQP is a good low level supported protocol as it's a very complex protocol to set up and support. Also brokers are known to have their differences in standard implementation which means supporting them all is a mess. It looks like the most accepted route is the libvirt route of having a c library abstracting away client server communication and having more advanced consumers build protocol specific bridges that may have different support standards. On a more personal note, I think brokerless messaging is the way to go in ovirt because, unlike traditional clustering, worker nodes are not interchangeable so direct communication is the way to go, rendering brokers pretty much useless. but brokerless doesn't let multiple consumers which a bus provides? All consumers can connect to the host and *some* events can be broadcasted to all connected clients. The real question is weather you want to depend on AMQP's routing \ message storing Also, if you find it preferable to have a centralized host (single point of failure) to get all events from all hosts for the price of some clients (I assume read only clients) not needing to know the locations of all worker nodes. But IMHO we already have something like that, it's called the ovirt-engine, and it could send aggregated events about the cluster (maybe with some extra enginy data). The question is what does mandating a broker gives us something that an AMQP bridge wouldn't. The only thing I can think of is vdsm can assume unmoderated vdsm to vdsm communication bypassing the engine. This means that VDSM can have some clustered behavior that requires no engine intervention. Further more, the engine can send a request and let the nodes decide who is performing the operation among themselves. Essentially: [ engine ] [ engine ] | | VS | [vdsm][vdsm] [ broker ] | | [vdsm][vdsm] *All links are two way links This has dire consequences on API usability and supportability. So we need to converge on that. There needs to be a good reason why the aforementioned logic code can't sit on a another ovirt specific entity (lets call it ovirt-dynamo) that uses VDSM's supported API but it's own APIs (or more likely messaging algorithms) are unsupported. [engine ] ||| | [ broker ] | ||| | [vdsm]-[dynamo] : [dynamo]-[vdsm] Host A : Host B *All links are two way links 1. we have engine today 'in the path' to the history db. but it makes no sense for engine to be aware of each statistic we want to keep in the history db. same would be for an event/stats correlation service. they don't need to depend on each other for availability/redundancy. 2. we are already looking at quantum integration, which is doing engine to nodes communication via amqp. 3. with somewhat of a forward looking - moving some scheduling logic down to vdsm will probably mean we'll want one of the nodes to listen to statistics and state from the other nodes. to all of these, setting up a bus which allows multiple peer listeners seems more robust ___ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://fedorahosted.org/mailman/listinfo/vdsm-devel
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
On 2012-7-10 2:52, Saggi Mizrahi wrote: - Original Message - From: Itamar Heim ih...@redhat.com To: Saggi Mizrahi smizr...@redhat.com Cc: Adam Litke a...@us.ibm.com, vdsm-devel@lists.fedorahosted.org Sent: Monday, July 9, 2012 11:03:43 AM Subject: Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm On 07/09/2012 05:56 PM, Saggi Mizrahi wrote: I don't think AMQP is a good low level supported protocol as it's a very complex protocol to set up and support. Also brokers are known to have their differences in standard implementation which means supporting them all is a mess. It looks like the most accepted route is the libvirt route of having a c library abstracting away client server communication and having more advanced consumers build protocol specific bridges that may have different support standards. On a more personal note, I think brokerless messaging is the way to go in ovirt because, unlike traditional clustering, worker nodes are not interchangeable so direct communication is the way to go, rendering brokers pretty much useless. but brokerless doesn't let multiple consumers which a bus provides? All consumers can connect to the host and *some* events can be broadcasted to all connected clients. The real question is weather you want to depend on AMQP's routing \ message storing Also, if you find it preferable to have a centralized host (single point of failure) to get all events from all hosts for the price of some clients (I assume read only clients) not needing to know the locations of all worker nodes. But IMHO we already have something like that, it's called the ovirt-engine, and it could send aggregated events about the cluster (maybe with some extra enginy data). The question is what does mandating a broker gives us something that an AMQP bridge wouldn't. The only thing I can think of is vdsm can assume unmoderated vdsm to vdsm communication bypassing the engine. I don't fully understand the sentence above. I think AMQP bridge can also provide a way for unmoderated vdsm to vdsm communication bypassing the engine. That is, one VDSM can post a message into the bridge and the other interested VDSM can consume the message. This means that VDSM can have some clustered behavior that requires no engine intervention. Further more, the engine can send a request and let the nodes decide who is performing the operation among themselves. Essentially: [ engine ] [ engine ] | | VS | [vdsm][vdsm] [ broker ] | | [vdsm][vdsm] *All links are two way links Where is the broker sit in? In one of the host nodes with VDSM? or in a specific node? This has dire consequences on API usability and supportability. So we need to converge on that. There needs to be a good reason why the aforementioned logic code can't sit on a another ovirt specific entity (lets call it ovirt-dynamo) that uses VDSM's supported API What aforementioned logic code you are talking about here? but it's own APIs (or more likely messaging algorithms) are unsupported. [engine ] ||| | [ broker ] | ||| | [vdsm]-[dynamo] : [dynamo]-[vdsm] Host A : Host B *All links are two way links - Original Message - From: Adam Litke a...@us.ibm.com To: Itamar Heim ih...@redhat.com Cc: vdsm-devel@lists.fedorahosted.org Sent: Monday, July 9, 2012 9:56:17 AM Subject: Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm On Fri, Jul 06, 2012 at 03:53:08PM +0300, Itamar Heim wrote: On 07/06/2012 01:15 AM, Robert Middleswarth wrote: On 07/05/2012 04:45 PM, Adam Litke wrote: On Thu, Jul 05, 2012 at 03:47:42PM -0400, Saggi Mizrahi wrote: - Original Message - From: Adam Litke a...@us.ibm.com To: Saggi Mizrahi smizr...@redhat.com Cc: Anthony Liguori anth...@codemonkey.ws, VDSM Project Development vdsm-devel@lists.fedorahosted.org Sent: Thursday, July 5, 2012 2:34:50 PM Subject: Re: [RFC] An alternative way to provide a supported interface -- libvdsm On Wed, Jun 27, 2012 at 02:50:02PM -0400, Saggi Mizrahi wrote: The idea of having a supported C API was something I was thinking about doing (But I'd rather use gobject introspection and not schema generation) But the problem is not having a C API is using the current XML RPC API as it's base I want to disect this a bit to find out exactly where there might be agreement and disagreement. C API is a good thing to implement - Agreed. I also want to use gobject introspection but I don't agree that using glib precludes the use of a formalized schema. My proposal is that we write a schema definition and generate the glib C code from that schema. I agree that the _current_ xmlrpc API makes a pretty bad base from which to start a supportable API.
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
On Thu, Jul 12, 2012 at 08:11:17AM +0800, Shu Ming wrote: Basically, my understanding is that we can generate two versions of libvdsm from the schema file for both the node and the management application. First, the transportation protocols(XMLRPC, REST-API) will depend on libvdsm(node version) to export the APIs to remote management application. Secondly, the management application can use libvdsm(application version ) to emit the remote call to the node. Also, transportation protocols like REST API and XML RPC API can also be generated automatically by the schema file with C, Java, Python bindings. I think this might be a bit too complex of a model. Here's how I see it... The schema generates C/gObject code which can be compiled into libvdsm. We can use the gObject introspection library to automatically generate language bindings for Java, Python, Perl, etc. The libvdsm library talks to vdsmd using a wire protocol that works locally and remotely. This wire protocol is completely hidden from library users. It's an implementation detail that can be changed later if necessary. Today I would recommend that we use xmlrpc. This means that ovirt-engine or another remote program could use libvdsm in the exact same manner as a local program. The library user just needs to call libvdsm.connect(uri). Finally, REST and AMQP bridges would be written solely against libvdsm. These bridges are probably not suitable for code generation (but we can revisit that as a separate issue because it's up to the bridge writer to determine the best approach). On 2012-7-12 2:29, Saggi Mizrahi wrote: I'm sorry, but I don't really understand the drawing - Original Message - From: Shu Ming shum...@linux.vnet.ibm.com To: Adam Litke a...@us.ibm.com Cc: vdsm-devel@lists.fedorahosted.org Sent: Wednesday, July 11, 2012 10:24:49 AM Subject: Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm Adam, Maybe, I don't fully understand your proposal. Here is my understanding of libvdsm in the picture. Please check the following link for the picture. http://www.ovirt.org/wiki/File:Libvdsm.JPG http://www.ovirt.org/wiki/File:Libvdsm.JPG On 2012-7-9 21:56, Adam Litke wrote: On Fri, Jul 06, 2012 at 03:53:08PM +0300, Itamar Heim wrote: On 07/06/2012 01:15 AM, Robert Middleswarth wrote: On 07/05/2012 04:45 PM, Adam Litke wrote: On Thu, Jul 05, 2012 at 03:47:42PM -0400, Saggi Mizrahi wrote: - Original Message - From: Adam Litke a...@us.ibm.com To: Saggi Mizrahi smizr...@redhat.com Cc: Anthony Liguori anth...@codemonkey.ws, VDSM Project Development vdsm-devel@lists.fedorahosted.org Sent: Thursday, July 5, 2012 2:34:50 PM Subject: Re: [RFC] An alternative way to provide a supported interface -- libvdsm On Wed, Jun 27, 2012 at 02:50:02PM -0400, Saggi Mizrahi wrote: The idea of having a supported C API was something I was thinking about doing (But I'd rather use gobject introspection and not schema generation) But the problem is not having a C API is using the current XML RPC API as it's base I want to disect this a bit to find out exactly where there might be agreement and disagreement. C API is a good thing to implement - Agreed. I also want to use gobject introspection but I don't agree that using glib precludes the use of a formalized schema. My proposal is that we write a schema definition and generate the glib C code from that schema. I agree that the _current_ xmlrpc API makes a pretty bad base from which to start a supportable API. XMLRPC is a perfectly reasonable remote/wire protocol and I think we should continue using it as a base for the next generation API. Using a schema will ensure that the new API is well-structured. There major problems with XML-RPC (and to some extent with REST as well) are high call overhead and no two way communication (push events). Basing on XML-RPC means that we will never be able to solve these issues. I am not sure I am ready to conceed that XML-RPC is too slow for our needs. Can you provide some more detail around this point and possibly suggest an alternative that has even lower overhead without sacrificing the ubiquity and usability of XML-RPC? As far as the two-way communication point, what are the options besides AMQP/ZeroMQ? Aren't these even worse from an overhead perspective than XML-RPC? Regarding two-way communication: you can write AMQP brokers based on the C API and run one on each vdsm host. Assuming the C API supports events, what else would you need? I personally think that using something like AMQP for inter-node communication and engine - node would be optimal. With a rest interface that just send messages though something like AMQP. I would also not dismiss AMQP so soon we want a bug with more than a single listener at engine side (engine, history db, maybe event correlation service). collectd as a means
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
On 2012-7-12 20:41, Adam Litke wrote: On Thu, Jul 12, 2012 at 08:11:17AM +0800, Shu Ming wrote: Basically, my understanding is that we can generate two versions of libvdsm from the schema file for both the node and the management application. First, the transportation protocols(XMLRPC, REST-API) will depend on libvdsm(node version) to export the APIs to remote management application. Secondly, the management application can use libvdsm(application version ) to emit the remote call to the node. Also, transportation protocols like REST API and XML RPC API can also be generated automatically by the schema file with C, Java, Python bindings. I think this might be a bit too complex of a model. Here's how I see it... The schema generates C/gObject code which can be compiled into libvdsm. We can use the gObject introspection library to automatically generate language bindings for Java, Python, Perl, etc. Do you mean Java, Python, Perl, etc bindings of libvdsm? The libvdsm library talks to vdsmd using a wire protocol that works locally and remotely. This wire protocol is completely hidden from library users. It's an implementation detail that can be changed later if necessary. Today I would recommend that we use xmlrpc. This means that ovirt-engine or another remote program could use libvdsm in the exact same manner as a local program. The library user just needs to call libvdsm.connect(uri). Except libvdsm.connet() or libvdsm.disconnet(), do you expect the engine will not change any of its xml-rpc interfaces now after libvdsm is introduced? I mean engine may not want to change much of its current code, so it expect the least change. Finally, REST and AMQP bridges would be written solely against libvdsm. These So we should write REST, AMQP bridges manually with Java, Python, Perl language on various bindings of libvdsm? bridges are probably not suitable for code generation (but we can revisit that as a separate issue because it's up to the bridge writer to determine the best approach). On 2012-7-12 2:29, Saggi Mizrahi wrote: I'm sorry, but I don't really understand the drawing - Original Message - From: Shu Ming shum...@linux.vnet.ibm.com To: Adam Litke a...@us.ibm.com Cc: vdsm-devel@lists.fedorahosted.org Sent: Wednesday, July 11, 2012 10:24:49 AM Subject: Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm Adam, Maybe, I don't fully understand your proposal. Here is my understanding of libvdsm in the picture. Please check the following link for the picture. http://www.ovirt.org/wiki/File:Libvdsm.JPG http://www.ovirt.org/wiki/File:Libvdsm.JPG On 2012-7-9 21:56, Adam Litke wrote: On Fri, Jul 06, 2012 at 03:53:08PM +0300, Itamar Heim wrote: On 07/06/2012 01:15 AM, Robert Middleswarth wrote: On 07/05/2012 04:45 PM, Adam Litke wrote: On Thu, Jul 05, 2012 at 03:47:42PM -0400, Saggi Mizrahi wrote: - Original Message - From: Adam Litke a...@us.ibm.com To: Saggi Mizrahi smizr...@redhat.com Cc: Anthony Liguori anth...@codemonkey.ws, VDSM Project Development vdsm-devel@lists.fedorahosted.org Sent: Thursday, July 5, 2012 2:34:50 PM Subject: Re: [RFC] An alternative way to provide a supported interface -- libvdsm On Wed, Jun 27, 2012 at 02:50:02PM -0400, Saggi Mizrahi wrote: The idea of having a supported C API was something I was thinking about doing (But I'd rather use gobject introspection and not schema generation) But the problem is not having a C API is using the current XML RPC API as it's base I want to disect this a bit to find out exactly where there might be agreement and disagreement. C API is a good thing to implement - Agreed. I also want to use gobject introspection but I don't agree that using glib precludes the use of a formalized schema. My proposal is that we write a schema definition and generate the glib C code from that schema. I agree that the _current_ xmlrpc API makes a pretty bad base from which to start a supportable API. XMLRPC is a perfectly reasonable remote/wire protocol and I think we should continue using it as a base for the next generation API. Using a schema will ensure that the new API is well-structured. There major problems with XML-RPC (and to some extent with REST as well) are high call overhead and no two way communication (push events). Basing on XML-RPC means that we will never be able to solve these issues. I am not sure I am ready to conceed that XML-RPC is too slow for our needs. Can you provide some more detail around this point and possibly suggest an alternative that has even lower overhead without sacrificing the ubiquity and usability of XML-RPC? As far as the two-way communication point, what are the options besides AMQP/ZeroMQ? Aren't these even worse from an overhead perspective than XML-RPC? Regarding two-way communication: you can write AMQP brokers based on the C API and run one on each vdsm host. Assuming the C API supports events, what else would
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
I'm sorry, but I don't really understand the drawing - Original Message - From: Shu Ming shum...@linux.vnet.ibm.com To: Adam Litke a...@us.ibm.com Cc: vdsm-devel@lists.fedorahosted.org Sent: Wednesday, July 11, 2012 10:24:49 AM Subject: Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm Adam, Maybe, I don't fully understand your proposal. Here is my understanding of libvdsm in the picture. Please check the following link for the picture. http://www.ovirt.org/wiki/File:Libvdsm.JPG http://www.ovirt.org/wiki/File:Libvdsm.JPG On 2012-7-9 21:56, Adam Litke wrote: On Fri, Jul 06, 2012 at 03:53:08PM +0300, Itamar Heim wrote: On 07/06/2012 01:15 AM, Robert Middleswarth wrote: On 07/05/2012 04:45 PM, Adam Litke wrote: On Thu, Jul 05, 2012 at 03:47:42PM -0400, Saggi Mizrahi wrote: - Original Message - From: Adam Litke a...@us.ibm.com To: Saggi Mizrahi smizr...@redhat.com Cc: Anthony Liguori anth...@codemonkey.ws, VDSM Project Development vdsm-devel@lists.fedorahosted.org Sent: Thursday, July 5, 2012 2:34:50 PM Subject: Re: [RFC] An alternative way to provide a supported interface -- libvdsm On Wed, Jun 27, 2012 at 02:50:02PM -0400, Saggi Mizrahi wrote: The idea of having a supported C API was something I was thinking about doing (But I'd rather use gobject introspection and not schema generation) But the problem is not having a C API is using the current XML RPC API as it's base I want to disect this a bit to find out exactly where there might be agreement and disagreement. C API is a good thing to implement - Agreed. I also want to use gobject introspection but I don't agree that using glib precludes the use of a formalized schema. My proposal is that we write a schema definition and generate the glib C code from that schema. I agree that the _current_ xmlrpc API makes a pretty bad base from which to start a supportable API. XMLRPC is a perfectly reasonable remote/wire protocol and I think we should continue using it as a base for the next generation API. Using a schema will ensure that the new API is well-structured. There major problems with XML-RPC (and to some extent with REST as well) are high call overhead and no two way communication (push events). Basing on XML-RPC means that we will never be able to solve these issues. I am not sure I am ready to conceed that XML-RPC is too slow for our needs. Can you provide some more detail around this point and possibly suggest an alternative that has even lower overhead without sacrificing the ubiquity and usability of XML-RPC? As far as the two-way communication point, what are the options besides AMQP/ZeroMQ? Aren't these even worse from an overhead perspective than XML-RPC? Regarding two-way communication: you can write AMQP brokers based on the C API and run one on each vdsm host. Assuming the C API supports events, what else would you need? I personally think that using something like AMQP for inter-node communication and engine - node would be optimal. With a rest interface that just send messages though something like AMQP. I would also not dismiss AMQP so soon we want a bug with more than a single listener at engine side (engine, history db, maybe event correlation service). collectd as a means for statistics already supports it as well. I'm for having REST as well, but not sure as main one for a consumer like ovirt engine. I agree that a message bus could be a very useful model of communication between ovirt-engine components and multiple vdsm instances. But the complexities and dependencies of AMQP do not make it suitable for use as a low-level API. AMQP will repel new adopters. Why not establish a libvdsm that is more minimalist and can be easily used by everyone? Then AMQP brokers can be built on top of the stable API with ease. All AMQP should require of the low-level API are standard function calls and an events mechanism. Thanks Robert The current XML-RPC API contains a lot of decencies and inefficiencies and we would like to retire it as soon as we possibly can. Engine would like us to move to a message based API and 3rd parties want something simple like REST so it looks like no one actually wants to use XML-RPC. Not even us. I am proposing that AMQP brokers and REST APIs could be written against the public API. In fact, they need not even live in the vdsm tree anymore if that is what we choose. Core vdsm would only be responsible for providing libvdsm and whatever language bindings we want to support. If we take the libvdsm route, the only reason to even have a REST bridge is only to support OSes other then Linux which is something I'm not sure we care about at the moment. That might be true regarding the current in-tree
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
Basically, my understanding is that we can generate two versions of libvdsm from the schema file for both the node and the management application. First, the transportation protocols(XMLRPC, REST-API) will depend on libvdsm(node version) to export the APIs to remote management application. Secondly, the management application can use libvdsm(application version ) to emit the remote call to the node. Also, transportation protocols like REST API and XML RPC API can also be generated automatically by the schema file with C, Java, Python bindings. On 2012-7-12 2:29, Saggi Mizrahi wrote: I'm sorry, but I don't really understand the drawing - Original Message - From: Shu Ming shum...@linux.vnet.ibm.com To: Adam Litke a...@us.ibm.com Cc: vdsm-devel@lists.fedorahosted.org Sent: Wednesday, July 11, 2012 10:24:49 AM Subject: Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm Adam, Maybe, I don't fully understand your proposal. Here is my understanding of libvdsm in the picture. Please check the following link for the picture. http://www.ovirt.org/wiki/File:Libvdsm.JPG http://www.ovirt.org/wiki/File:Libvdsm.JPG On 2012-7-9 21:56, Adam Litke wrote: On Fri, Jul 06, 2012 at 03:53:08PM +0300, Itamar Heim wrote: On 07/06/2012 01:15 AM, Robert Middleswarth wrote: On 07/05/2012 04:45 PM, Adam Litke wrote: On Thu, Jul 05, 2012 at 03:47:42PM -0400, Saggi Mizrahi wrote: - Original Message - From: Adam Litke a...@us.ibm.com To: Saggi Mizrahi smizr...@redhat.com Cc: Anthony Liguori anth...@codemonkey.ws, VDSM Project Development vdsm-devel@lists.fedorahosted.org Sent: Thursday, July 5, 2012 2:34:50 PM Subject: Re: [RFC] An alternative way to provide a supported interface -- libvdsm On Wed, Jun 27, 2012 at 02:50:02PM -0400, Saggi Mizrahi wrote: The idea of having a supported C API was something I was thinking about doing (But I'd rather use gobject introspection and not schema generation) But the problem is not having a C API is using the current XML RPC API as it's base I want to disect this a bit to find out exactly where there might be agreement and disagreement. C API is a good thing to implement - Agreed. I also want to use gobject introspection but I don't agree that using glib precludes the use of a formalized schema. My proposal is that we write a schema definition and generate the glib C code from that schema. I agree that the _current_ xmlrpc API makes a pretty bad base from which to start a supportable API. XMLRPC is a perfectly reasonable remote/wire protocol and I think we should continue using it as a base for the next generation API. Using a schema will ensure that the new API is well-structured. There major problems with XML-RPC (and to some extent with REST as well) are high call overhead and no two way communication (push events). Basing on XML-RPC means that we will never be able to solve these issues. I am not sure I am ready to conceed that XML-RPC is too slow for our needs. Can you provide some more detail around this point and possibly suggest an alternative that has even lower overhead without sacrificing the ubiquity and usability of XML-RPC? As far as the two-way communication point, what are the options besides AMQP/ZeroMQ? Aren't these even worse from an overhead perspective than XML-RPC? Regarding two-way communication: you can write AMQP brokers based on the C API and run one on each vdsm host. Assuming the C API supports events, what else would you need? I personally think that using something like AMQP for inter-node communication and engine - node would be optimal. With a rest interface that just send messages though something like AMQP. I would also not dismiss AMQP so soon we want a bug with more than a single listener at engine side (engine, history db, maybe event correlation service). collectd as a means for statistics already supports it as well. I'm for having REST as well, but not sure as main one for a consumer like ovirt engine. I agree that a message bus could be a very useful model of communication between ovirt-engine components and multiple vdsm instances. But the complexities and dependencies of AMQP do not make it suitable for use as a low-level API. AMQP will repel new adopters. Why not establish a libvdsm that is more minimalist and can be easily used by everyone? Then AMQP brokers can be built on top of the stable API with ease. All AMQP should require of the low-level API are standard function calls and an events mechanism. Thanks Robert The current XML-RPC API contains a lot of decencies and inefficiencies and we would like to retire it as soon as we possibly can. Engine would like us to move to a message based API and 3rd parties want something simple like REST so it looks like no one actually wants to use XML-RPC. Not even us. I am proposing that AMQP brokers and REST APIs could be written against the public API. In fact, they need not even live in the vdsm tree
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
On Fri, Jul 06, 2012 at 03:53:08PM +0300, Itamar Heim wrote: On 07/06/2012 01:15 AM, Robert Middleswarth wrote: On 07/05/2012 04:45 PM, Adam Litke wrote: On Thu, Jul 05, 2012 at 03:47:42PM -0400, Saggi Mizrahi wrote: - Original Message - From: Adam Litke a...@us.ibm.com To: Saggi Mizrahi smizr...@redhat.com Cc: Anthony Liguori anth...@codemonkey.ws, VDSM Project Development vdsm-devel@lists.fedorahosted.org Sent: Thursday, July 5, 2012 2:34:50 PM Subject: Re: [RFC] An alternative way to provide a supported interface -- libvdsm On Wed, Jun 27, 2012 at 02:50:02PM -0400, Saggi Mizrahi wrote: The idea of having a supported C API was something I was thinking about doing (But I'd rather use gobject introspection and not schema generation) But the problem is not having a C API is using the current XML RPC API as it's base I want to disect this a bit to find out exactly where there might be agreement and disagreement. C API is a good thing to implement - Agreed. I also want to use gobject introspection but I don't agree that using glib precludes the use of a formalized schema. My proposal is that we write a schema definition and generate the glib C code from that schema. I agree that the _current_ xmlrpc API makes a pretty bad base from which to start a supportable API. XMLRPC is a perfectly reasonable remote/wire protocol and I think we should continue using it as a base for the next generation API. Using a schema will ensure that the new API is well-structured. There major problems with XML-RPC (and to some extent with REST as well) are high call overhead and no two way communication (push events). Basing on XML-RPC means that we will never be able to solve these issues. I am not sure I am ready to conceed that XML-RPC is too slow for our needs. Can you provide some more detail around this point and possibly suggest an alternative that has even lower overhead without sacrificing the ubiquity and usability of XML-RPC? As far as the two-way communication point, what are the options besides AMQP/ZeroMQ? Aren't these even worse from an overhead perspective than XML-RPC? Regarding two-way communication: you can write AMQP brokers based on the C API and run one on each vdsm host. Assuming the C API supports events, what else would you need? I personally think that using something like AMQP for inter-node communication and engine - node would be optimal. With a rest interface that just send messages though something like AMQP. I would also not dismiss AMQP so soon we want a bug with more than a single listener at engine side (engine, history db, maybe event correlation service). collectd as a means for statistics already supports it as well. I'm for having REST as well, but not sure as main one for a consumer like ovirt engine. I agree that a message bus could be a very useful model of communication between ovirt-engine components and multiple vdsm instances. But the complexities and dependencies of AMQP do not make it suitable for use as a low-level API. AMQP will repel new adopters. Why not establish a libvdsm that is more minimalist and can be easily used by everyone? Then AMQP brokers can be built on top of the stable API with ease. All AMQP should require of the low-level API are standard function calls and an events mechanism. Thanks Robert The current XML-RPC API contains a lot of decencies and inefficiencies and we would like to retire it as soon as we possibly can. Engine would like us to move to a message based API and 3rd parties want something simple like REST so it looks like no one actually wants to use XML-RPC. Not even us. I am proposing that AMQP brokers and REST APIs could be written against the public API. In fact, they need not even live in the vdsm tree anymore if that is what we choose. Core vdsm would only be responsible for providing libvdsm and whatever language bindings we want to support. If we take the libvdsm route, the only reason to even have a REST bridge is only to support OSes other then Linux which is something I'm not sure we care about at the moment. That might be true regarding the current in-tree implementation. However, I can almost guarantee that someone wanting to write a web GUI on top of standalone vdsm would want a REST API to talk to. But libvdsm makes this use case of no concern to the core vdsm developers. I do think that having C supportability in our API is a good idea, but the current API should not be used as the base. Let's _start_ with a schema document that describes today's API and then clean it up. I think that will work better than starting from scratch. Once my schema is written I will post it and we can 'patch' it as a community until we arrive at a 1.0 version we are all happy with. +1 Ok. Redoubling my efforts to get this done. Describing the output of list(True) takes awhile :)
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
I don't think AMQP is a good low level supported protocol as it's a very complex protocol to set up and support. Also brokers are known to have their differences in standard implementation which means supporting them all is a mess. It looks like the most accepted route is the libvirt route of having a c library abstracting away client server communication and having more advanced consumers build protocol specific bridges that may have different support standards. On a more personal note, I think brokerless messaging is the way to go in ovirt because, unlike traditional clustering, worker nodes are not interchangeable so direct communication is the way to go, rendering brokers pretty much useless. - Original Message - From: Adam Litke a...@us.ibm.com To: Itamar Heim ih...@redhat.com Cc: vdsm-devel@lists.fedorahosted.org Sent: Monday, July 9, 2012 9:56:17 AM Subject: Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm On Fri, Jul 06, 2012 at 03:53:08PM +0300, Itamar Heim wrote: On 07/06/2012 01:15 AM, Robert Middleswarth wrote: On 07/05/2012 04:45 PM, Adam Litke wrote: On Thu, Jul 05, 2012 at 03:47:42PM -0400, Saggi Mizrahi wrote: - Original Message - From: Adam Litke a...@us.ibm.com To: Saggi Mizrahi smizr...@redhat.com Cc: Anthony Liguori anth...@codemonkey.ws, VDSM Project Development vdsm-devel@lists.fedorahosted.org Sent: Thursday, July 5, 2012 2:34:50 PM Subject: Re: [RFC] An alternative way to provide a supported interface -- libvdsm On Wed, Jun 27, 2012 at 02:50:02PM -0400, Saggi Mizrahi wrote: The idea of having a supported C API was something I was thinking about doing (But I'd rather use gobject introspection and not schema generation) But the problem is not having a C API is using the current XML RPC API as it's base I want to disect this a bit to find out exactly where there might be agreement and disagreement. C API is a good thing to implement - Agreed. I also want to use gobject introspection but I don't agree that using glib precludes the use of a formalized schema. My proposal is that we write a schema definition and generate the glib C code from that schema. I agree that the _current_ xmlrpc API makes a pretty bad base from which to start a supportable API. XMLRPC is a perfectly reasonable remote/wire protocol and I think we should continue using it as a base for the next generation API. Using a schema will ensure that the new API is well-structured. There major problems with XML-RPC (and to some extent with REST as well) are high call overhead and no two way communication (push events). Basing on XML-RPC means that we will never be able to solve these issues. I am not sure I am ready to conceed that XML-RPC is too slow for our needs. Can you provide some more detail around this point and possibly suggest an alternative that has even lower overhead without sacrificing the ubiquity and usability of XML-RPC? As far as the two-way communication point, what are the options besides AMQP/ZeroMQ? Aren't these even worse from an overhead perspective than XML-RPC? Regarding two-way communication: you can write AMQP brokers based on the C API and run one on each vdsm host. Assuming the C API supports events, what else would you need? I personally think that using something like AMQP for inter-node communication and engine - node would be optimal. With a rest interface that just send messages though something like AMQP. I would also not dismiss AMQP so soon we want a bug with more than a single listener at engine side (engine, history db, maybe event correlation service). collectd as a means for statistics already supports it as well. I'm for having REST as well, but not sure as main one for a consumer like ovirt engine. I agree that a message bus could be a very useful model of communication between ovirt-engine components and multiple vdsm instances. But the complexities and dependencies of AMQP do not make it suitable for use as a low-level API. AMQP will repel new adopters. Why not establish a libvdsm that is more minimalist and can be easily used by everyone? Then AMQP brokers can be built on top of the stable API with ease. All AMQP should require of the low-level API are standard function calls and an events mechanism. Thanks Robert The current XML-RPC API contains a lot of decencies and inefficiencies and we would like to retire it as soon as we possibly can. Engine would like us to move to a message based API and 3rd parties want something simple like REST so it looks like no one actually wants to use XML-RPC. Not even us. I am proposing that AMQP brokers and REST APIs could be written against the public API. In fact, they need not even live in the vdsm tree anymore if that is what we choose.
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
On 07/09/2012 05:56 PM, Saggi Mizrahi wrote: I don't think AMQP is a good low level supported protocol as it's a very complex protocol to set up and support. Also brokers are known to have their differences in standard implementation which means supporting them all is a mess. It looks like the most accepted route is the libvirt route of having a c library abstracting away client server communication and having more advanced consumers build protocol specific bridges that may have different support standards. On a more personal note, I think brokerless messaging is the way to go in ovirt because, unlike traditional clustering, worker nodes are not interchangeable so direct communication is the way to go, rendering brokers pretty much useless. but brokerless doesn't let multiple consumers which a bus provides? - Original Message - From: Adam Litke a...@us.ibm.com To: Itamar Heim ih...@redhat.com Cc: vdsm-devel@lists.fedorahosted.org Sent: Monday, July 9, 2012 9:56:17 AM Subject: Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm On Fri, Jul 06, 2012 at 03:53:08PM +0300, Itamar Heim wrote: On 07/06/2012 01:15 AM, Robert Middleswarth wrote: On 07/05/2012 04:45 PM, Adam Litke wrote: On Thu, Jul 05, 2012 at 03:47:42PM -0400, Saggi Mizrahi wrote: - Original Message - From: Adam Litke a...@us.ibm.com To: Saggi Mizrahi smizr...@redhat.com Cc: Anthony Liguori anth...@codemonkey.ws, VDSM Project Development vdsm-devel@lists.fedorahosted.org Sent: Thursday, July 5, 2012 2:34:50 PM Subject: Re: [RFC] An alternative way to provide a supported interface -- libvdsm On Wed, Jun 27, 2012 at 02:50:02PM -0400, Saggi Mizrahi wrote: The idea of having a supported C API was something I was thinking about doing (But I'd rather use gobject introspection and not schema generation) But the problem is not having a C API is using the current XML RPC API as it's base I want to disect this a bit to find out exactly where there might be agreement and disagreement. C API is a good thing to implement - Agreed. I also want to use gobject introspection but I don't agree that using glib precludes the use of a formalized schema. My proposal is that we write a schema definition and generate the glib C code from that schema. I agree that the _current_ xmlrpc API makes a pretty bad base from which to start a supportable API. XMLRPC is a perfectly reasonable remote/wire protocol and I think we should continue using it as a base for the next generation API. Using a schema will ensure that the new API is well-structured. There major problems with XML-RPC (and to some extent with REST as well) are high call overhead and no two way communication (push events). Basing on XML-RPC means that we will never be able to solve these issues. I am not sure I am ready to conceed that XML-RPC is too slow for our needs. Can you provide some more detail around this point and possibly suggest an alternative that has even lower overhead without sacrificing the ubiquity and usability of XML-RPC? As far as the two-way communication point, what are the options besides AMQP/ZeroMQ? Aren't these even worse from an overhead perspective than XML-RPC? Regarding two-way communication: you can write AMQP brokers based on the C API and run one on each vdsm host. Assuming the C API supports events, what else would you need? I personally think that using something like AMQP for inter-node communication and engine - node would be optimal. With a rest interface that just send messages though something like AMQP. I would also not dismiss AMQP so soon we want a bug with more than a single listener at engine side (engine, history db, maybe event correlation service). collectd as a means for statistics already supports it as well. I'm for having REST as well, but not sure as main one for a consumer like ovirt engine. I agree that a message bus could be a very useful model of communication between ovirt-engine components and multiple vdsm instances. But the complexities and dependencies of AMQP do not make it suitable for use as a low-level API. AMQP will repel new adopters. Why not establish a libvdsm that is more minimalist and can be easily used by everyone? Then AMQP brokers can be built on top of the stable API with ease. All AMQP should require of the low-level API are standard function calls and an events mechanism. Thanks Robert The current XML-RPC API contains a lot of decencies and inefficiencies and we would like to retire it as soon as we possibly can. Engine would like us to move to a message based API and 3rd parties want something simple like REST so it looks like no one actually wants to use XML-RPC. Not even us. I am proposing that AMQP brokers and REST APIs could be written against the public API. In fact, they need not even live in the vdsm tree anymore if that is what we choose. Core vdsm would only be responsible for providing libvdsm and whatever language bindings
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
- Original Message - From: Itamar Heim ih...@redhat.com To: Saggi Mizrahi smizr...@redhat.com Cc: Adam Litke a...@us.ibm.com, vdsm-devel@lists.fedorahosted.org Sent: Monday, July 9, 2012 11:03:43 AM Subject: Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm On 07/09/2012 05:56 PM, Saggi Mizrahi wrote: I don't think AMQP is a good low level supported protocol as it's a very complex protocol to set up and support. Also brokers are known to have their differences in standard implementation which means supporting them all is a mess. It looks like the most accepted route is the libvirt route of having a c library abstracting away client server communication and having more advanced consumers build protocol specific bridges that may have different support standards. On a more personal note, I think brokerless messaging is the way to go in ovirt because, unlike traditional clustering, worker nodes are not interchangeable so direct communication is the way to go, rendering brokers pretty much useless. but brokerless doesn't let multiple consumers which a bus provides? All consumers can connect to the host and *some* events can be broadcasted to all connected clients. The real question is weather you want to depend on AMQP's routing \ message storing Also, if you find it preferable to have a centralized host (single point of failure) to get all events from all hosts for the price of some clients (I assume read only clients) not needing to know the locations of all worker nodes. But IMHO we already have something like that, it's called the ovirt-engine, and it could send aggregated events about the cluster (maybe with some extra enginy data). The question is what does mandating a broker gives us something that an AMQP bridge wouldn't. The only thing I can think of is vdsm can assume unmoderated vdsm to vdsm communication bypassing the engine. This means that VDSM can have some clustered behavior that requires no engine intervention. Further more, the engine can send a request and let the nodes decide who is performing the operation among themselves. Essentially: [ engine ] [ engine ] | | VS | [vdsm][vdsm] [ broker ] | | [vdsm][vdsm] *All links are two way links This has dire consequences on API usability and supportability. So we need to converge on that. There needs to be a good reason why the aforementioned logic code can't sit on a another ovirt specific entity (lets call it ovirt-dynamo) that uses VDSM's supported API but it's own APIs (or more likely messaging algorithms) are unsupported. [engine ] ||| | [ broker ] | ||| | [vdsm]-[dynamo] : [dynamo]-[vdsm] Host A : Host B *All links are two way links - Original Message - From: Adam Litke a...@us.ibm.com To: Itamar Heim ih...@redhat.com Cc: vdsm-devel@lists.fedorahosted.org Sent: Monday, July 9, 2012 9:56:17 AM Subject: Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm On Fri, Jul 06, 2012 at 03:53:08PM +0300, Itamar Heim wrote: On 07/06/2012 01:15 AM, Robert Middleswarth wrote: On 07/05/2012 04:45 PM, Adam Litke wrote: On Thu, Jul 05, 2012 at 03:47:42PM -0400, Saggi Mizrahi wrote: - Original Message - From: Adam Litke a...@us.ibm.com To: Saggi Mizrahi smizr...@redhat.com Cc: Anthony Liguori anth...@codemonkey.ws, VDSM Project Development vdsm-devel@lists.fedorahosted.org Sent: Thursday, July 5, 2012 2:34:50 PM Subject: Re: [RFC] An alternative way to provide a supported interface -- libvdsm On Wed, Jun 27, 2012 at 02:50:02PM -0400, Saggi Mizrahi wrote: The idea of having a supported C API was something I was thinking about doing (But I'd rather use gobject introspection and not schema generation) But the problem is not having a C API is using the current XML RPC API as it's base I want to disect this a bit to find out exactly where there might be agreement and disagreement. C API is a good thing to implement - Agreed. I also want to use gobject introspection but I don't agree that using glib precludes the use of a formalized schema. My proposal is that we write a schema definition and generate the glib C code from that schema. I agree that the _current_ xmlrpc API makes a pretty bad base from which to start a supportable API. XMLRPC is a perfectly reasonable remote/wire protocol and I think we should continue using it as a base for the next generation API. Using a schema will ensure that the new API is well-structured. There major problems with XML-RPC (and to some extent with REST as well) are high call overhead and no two way communication (push
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
On Fri, Jul 06, 2012 at 07:17:44AM -0500, Adam Litke wrote: Adding danpb and DV to get some perspective from libvirt... On Thu, Jul 05, 2012 at 05:02:59PM -0400, Saggi Mizrahi wrote: I am not sure I am ready to conceed that XML-RPC is too slow for our needs. Can you provide some more detail around this point and possibly suggest an alternative that has even lower overhead without sacrificing the ubiquity and usability of XML-RPC? As far as the two-way communication point, what are the options besides AMQP/ZeroMQ? Aren't these even worse from an overhead perspective than XML-RPC? Regarding two-way communication: you can write AMQP brokers based on the C API and run one on each vdsm host. Assuming the C API supports events, what else would you need? If we plan to go with the libvdsm route the only transports I think are appropriate are either raw sockets (like libvirt) or ZMQ (just to take advantage of it managing connection and message encapsulation but it might be an overkill). Other then that ZMQ\AMQP\REST\XML-RPC bridges are not really a priority for me as engine will not be using any of the bridges. I think (and others have also suggested) that ZMQ is not very suitable as the foundation of an API due to it's heavy weight. I would really appreciate the perspective of the libvirt guys and others in the community on this topic. Between you and I, the only approach that hasn't been nacked is: raw sockets and xdr ala libvirt. Are there any detractors of this idea? Anything better to consider? xdr is ancient :) I think I've already given my views on this earlier in the thread. To recap, I think that it is very important for the core functionality of VDSM to be easy to get up running / deployment. Adding a serious messaging layer like AMQP or similar, as a mandatory component puts a non-negligable barrier to entry. Probably one of the most important things that drove adoption of libvirt was that you can use it remotely securely with no external infrastructure. You just start libvirtd can access it via its SSH tunnel facility. Of course for most production deployments you wouldn't use this, but it is important for encouraging developers to work on it making it easy for users to just try it out on a small scale. WRT to XDR, remember that it is not a protocol - it is simply a spec for how to encode various data structures in an efficient binary format. I don't think how old it is really relevant, since there's only so many different ways you want to encode binary data structures. Since it is just a data format encoding, you have the job of defining the actual RPC protocol on top of that. Now this isn't particularly hard to get going at first, but the complexity does add up over time. I'd still suggest aiming for some variant of REST for its simplicity and the fact that you can then use standard HTTP server client components and solely focus on your APIs, rather than infrastructure. Daniel -- |: http://berrange.com -o-http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :| ___ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://fedorahosted.org/mailman/listinfo/vdsm-devel
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
On 07/06/2012 01:15 AM, Robert Middleswarth wrote: On 07/05/2012 04:45 PM, Adam Litke wrote: On Thu, Jul 05, 2012 at 03:47:42PM -0400, Saggi Mizrahi wrote: - Original Message - From: Adam Litke a...@us.ibm.com To: Saggi Mizrahi smizr...@redhat.com Cc: Anthony Liguori anth...@codemonkey.ws, VDSM Project Development vdsm-devel@lists.fedorahosted.org Sent: Thursday, July 5, 2012 2:34:50 PM Subject: Re: [RFC] An alternative way to provide a supported interface -- libvdsm On Wed, Jun 27, 2012 at 02:50:02PM -0400, Saggi Mizrahi wrote: The idea of having a supported C API was something I was thinking about doing (But I'd rather use gobject introspection and not schema generation) But the problem is not having a C API is using the current XML RPC API as it's base I want to disect this a bit to find out exactly where there might be agreement and disagreement. C API is a good thing to implement - Agreed. I also want to use gobject introspection but I don't agree that using glib precludes the use of a formalized schema. My proposal is that we write a schema definition and generate the glib C code from that schema. I agree that the _current_ xmlrpc API makes a pretty bad base from which to start a supportable API. XMLRPC is a perfectly reasonable remote/wire protocol and I think we should continue using it as a base for the next generation API. Using a schema will ensure that the new API is well-structured. There major problems with XML-RPC (and to some extent with REST as well) are high call overhead and no two way communication (push events). Basing on XML-RPC means that we will never be able to solve these issues. I am not sure I am ready to conceed that XML-RPC is too slow for our needs. Can you provide some more detail around this point and possibly suggest an alternative that has even lower overhead without sacrificing the ubiquity and usability of XML-RPC? As far as the two-way communication point, what are the options besides AMQP/ZeroMQ? Aren't these even worse from an overhead perspective than XML-RPC? Regarding two-way communication: you can write AMQP brokers based on the C API and run one on each vdsm host. Assuming the C API supports events, what else would you need? I personally think that using something like AMQP for inter-node communication and engine - node would be optimal. With a rest interface that just send messages though something like AMQP. I would also not dismiss AMQP so soon we want a bug with more than a single listener at engine side (engine, history db, maybe event correlation service). collectd as a means for statistics already supports it as well. I'm for having REST as well, but not sure as main one for a consumer like ovirt engine. Thanks Robert The current XML-RPC API contains a lot of decencies and inefficiencies and we would like to retire it as soon as we possibly can. Engine would like us to move to a message based API and 3rd parties want something simple like REST so it looks like no one actually wants to use XML-RPC. Not even us. I am proposing that AMQP brokers and REST APIs could be written against the public API. In fact, they need not even live in the vdsm tree anymore if that is what we choose. Core vdsm would only be responsible for providing libvdsm and whatever language bindings we want to support. If we take the libvdsm route, the only reason to even have a REST bridge is only to support OSes other then Linux which is something I'm not sure we care about at the moment. That might be true regarding the current in-tree implementation. However, I can almost guarantee that someone wanting to write a web GUI on top of standalone vdsm would want a REST API to talk to. But libvdsm makes this use case of no concern to the core vdsm developers. I do think that having C supportability in our API is a good idea, but the current API should not be used as the base. Let's _start_ with a schema document that describes today's API and then clean it up. I think that will work better than starting from scratch. Once my schema is written I will post it and we can 'patch' it as a community until we arrive at a 1.0 version we are all happy with. +1 Ok. Redoubling my efforts to get this done. Describing the output of list(True) takes awhile :) ___ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://fedorahosted.org/mailman/listinfo/vdsm-devel ___ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://fedorahosted.org/mailman/listinfo/vdsm-devel
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
- Original Message - From: Adam Litke a...@us.ibm.com To: Saggi Mizrahi smizr...@redhat.com Cc: Anthony Liguori anth...@codemonkey.ws, VDSM Project Development vdsm-devel@lists.fedorahosted.org Sent: Thursday, July 5, 2012 4:45:08 PM Subject: Re: [RFC] An alternative way to provide a supported interface -- libvdsm On Thu, Jul 05, 2012 at 03:47:42PM -0400, Saggi Mizrahi wrote: - Original Message - From: Adam Litke a...@us.ibm.com To: Saggi Mizrahi smizr...@redhat.com Cc: Anthony Liguori anth...@codemonkey.ws, VDSM Project Development vdsm-devel@lists.fedorahosted.org Sent: Thursday, July 5, 2012 2:34:50 PM Subject: Re: [RFC] An alternative way to provide a supported interface -- libvdsm On Wed, Jun 27, 2012 at 02:50:02PM -0400, Saggi Mizrahi wrote: The idea of having a supported C API was something I was thinking about doing (But I'd rather use gobject introspection and not schema generation) But the problem is not having a C API is using the current XML RPC API as it's base I want to disect this a bit to find out exactly where there might be agreement and disagreement. C API is a good thing to implement - Agreed. I also want to use gobject introspection but I don't agree that using glib precludes the use of a formalized schema. My proposal is that we write a schema definition and generate the glib C code from that schema. I agree that the _current_ xmlrpc API makes a pretty bad base from which to start a supportable API. XMLRPC is a perfectly reasonable remote/wire protocol and I think we should continue using it as a base for the next generation API. Using a schema will ensure that the new API is well-structured. There major problems with XML-RPC (and to some extent with REST as well) are high call overhead and no two way communication (push events). Basing on XML-RPC means that we will never be able to solve these issues. I am not sure I am ready to conceed that XML-RPC is too slow for our needs. Can you provide some more detail around this point and possibly suggest an alternative that has even lower overhead without sacrificing the ubiquity and usability of XML-RPC? As far as the two-way communication point, what are the options besides AMQP/ZeroMQ? Aren't these even worse from an overhead perspective than XML-RPC? Regarding two-way communication: you can write AMQP brokers based on the C API and run one on each vdsm host. Assuming the C API supports events, what else would you need? If we plan to go with the libvdsm route the only transports I think are appropriate are either raw sockets (like libvirt) or ZMQ (just to take advantage of it managing connection and message encapsulation but it might be an overkill). Other then that ZMQ\AMQP\REST\XML-RPC bridges are not really a priority for me as engine will not be using any of the bridges. The current XML-RPC API contains a lot of decencies and inefficiencies and we would like to retire it as soon as we possibly can. Engine would like us to move to a message based API and 3rd parties want something simple like REST so it looks like no one actually wants to use XML-RPC. Not even us. I am proposing that AMQP brokers and REST APIs could be written against the public API. In fact, they need not even live in the vdsm tree anymore if that is what we choose. Core vdsm would only be responsible for providing libvdsm and whatever language bindings we want to support. If we take the libvdsm route, the only reason to even have a REST bridge is only to support OSes other then Linux which is something I'm not sure we care about at the moment. That might be true regarding the current in-tree implementation. However, I can almost guarantee that someone wanting to write a web GUI on top of standalone vdsm would want a REST API to talk to. But libvdsm makes this use case of no concern to the core vdsm developers. I do think that having C supportability in our API is a good idea, but the current API should not be used as the base. Let's _start_ with a schema document that describes today's API and then clean it up. I think that will work better than starting from scratch. Once my schema is written I will post it and we can 'patch' it as a community until we arrive at a 1.0 version we are all happy with. +1 Ok. Redoubling my efforts to get this done. Describing the output of list(True) takes awhile :) -- Adam Litke a...@us.ibm.com IBM Linux Technology Center ___ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://fedorahosted.org/mailman/listinfo/vdsm-devel
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
On 07/05/2012 04:45 PM, Adam Litke wrote: On Thu, Jul 05, 2012 at 03:47:42PM -0400, Saggi Mizrahi wrote: - Original Message - From: Adam Litke a...@us.ibm.com To: Saggi Mizrahi smizr...@redhat.com Cc: Anthony Liguori anth...@codemonkey.ws, VDSM Project Development vdsm-devel@lists.fedorahosted.org Sent: Thursday, July 5, 2012 2:34:50 PM Subject: Re: [RFC] An alternative way to provide a supported interface -- libvdsm On Wed, Jun 27, 2012 at 02:50:02PM -0400, Saggi Mizrahi wrote: The idea of having a supported C API was something I was thinking about doing (But I'd rather use gobject introspection and not schema generation) But the problem is not having a C API is using the current XML RPC API as it's base I want to disect this a bit to find out exactly where there might be agreement and disagreement. C API is a good thing to implement - Agreed. I also want to use gobject introspection but I don't agree that using glib precludes the use of a formalized schema. My proposal is that we write a schema definition and generate the glib C code from that schema. I agree that the _current_ xmlrpc API makes a pretty bad base from which to start a supportable API. XMLRPC is a perfectly reasonable remote/wire protocol and I think we should continue using it as a base for the next generation API. Using a schema will ensure that the new API is well-structured. There major problems with XML-RPC (and to some extent with REST as well) are high call overhead and no two way communication (push events). Basing on XML-RPC means that we will never be able to solve these issues. I am not sure I am ready to conceed that XML-RPC is too slow for our needs. Can you provide some more detail around this point and possibly suggest an alternative that has even lower overhead without sacrificing the ubiquity and usability of XML-RPC? As far as the two-way communication point, what are the options besides AMQP/ZeroMQ? Aren't these even worse from an overhead perspective than XML-RPC? Regarding two-way communication: you can write AMQP brokers based on the C API and run one on each vdsm host. Assuming the C API supports events, what else would you need? I personally think that using something like AMQP for inter-node communication and engine - node would be optimal. With a rest interface that just send messages though something like AMQP. Thanks Robert The current XML-RPC API contains a lot of decencies and inefficiencies and we would like to retire it as soon as we possibly can. Engine would like us to move to a message based API and 3rd parties want something simple like REST so it looks like no one actually wants to use XML-RPC. Not even us. I am proposing that AMQP brokers and REST APIs could be written against the public API. In fact, they need not even live in the vdsm tree anymore if that is what we choose. Core vdsm would only be responsible for providing libvdsm and whatever language bindings we want to support. If we take the libvdsm route, the only reason to even have a REST bridge is only to support OSes other then Linux which is something I'm not sure we care about at the moment. That might be true regarding the current in-tree implementation. However, I can almost guarantee that someone wanting to write a web GUI on top of standalone vdsm would want a REST API to talk to. But libvdsm makes this use case of no concern to the core vdsm developers. I do think that having C supportability in our API is a good idea, but the current API should not be used as the base. Let's _start_ with a schema document that describes today's API and then clean it up. I think that will work better than starting from scratch. Once my schema is written I will post it and we can 'patch' it as a community until we arrive at a 1.0 version we are all happy with. +1 Ok. Redoubling my efforts to get this done. Describing the output of list(True) takes awhile :) ___ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://fedorahosted.org/mailman/listinfo/vdsm-devel
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
The idea of having a supported C API was something I was thinking about doing (But I'd rather use gobject introspection and not schema generation) But the problem is not having a C API is using the current XML RPC API as it's base The current XML-RPC API contains a lot of decencies and inefficiencies and we would like to retire it as soon as we possibly can. Engine would like us to move to a message based API and 3rd parties want something simple like REST so it looks like no one actually wants to use XML-RPC. Not even us. I do think that having C supportability in our API is a good idea, but the current API should not be used as the base. - Original Message - From: Anthony Liguori anth...@codemonkey.ws To: VDSM Project Development vdsm-devel@lists.fedorahosted.org Cc: Adam Litke a...@us.ibm.com, Saggi Mizrahi smizr...@redhat.com Sent: Monday, June 25, 2012 10:18:33 AM Subject: [RFC] An alternative way to provide a supported interface -- libvdsm Hi, I've been reading through the API threads here and considering the options. To be honest, I worry a lot about the scope of these discussions and that there's a tremendous amount of work before we have a useful end result. I wonder if we can solve this problem by adding another layer of abstraction... As Adam is currently building a schema for VDSM's XML-RPC, we could use the QAPI code generators to build a libvdsm that provided a programmatic C interface for the XML-RPC interface. It would take some tweaking, but this could be made a supportable C interface. The rules for having a supportable C interface are basically: 1) Never change function signatures 2) Never remove functions 3) Always allocate structures in the library and/or pad 4) Only add to structures, never remove or reorder 5) Provide flags that default to zero to indicate that fields/features are not present. 6) Always zero-initialize structures Having a libvdsm would allow the transport to change over time w/o affecting end-users. There are lots of good tools for documenting C APIs and dealing with versioning of C APIs. While we can start out with a schema-generated API, over time, we can implement libvdsm in an open-coded fashion allowing old APIs to be reimplemented in terms of new APIs. From a compatibility perspective, libvdsm would be fully backwards compatible with old versions of VDSM (so it would keep XML-RPC support forever) but may require new versions of libvdsm to talk to new versions of VDSM. That would allow for APIs to be deprecated within VDSM without breaking old clients. I think this would be an incremental approach to building a supportable API today while still giving the flexibility to make changes in the long term. And it should be fairly easy to generate a JNI binding and also port ovirt-engine to use an interface like this (since it already uses the XML-RPC API). Regards, Anthony Liguori ___ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://fedorahosted.org/mailman/listinfo/vdsm-devel
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
- Original Message - The idea of having a supported C API was something I was thinking about doing (But I'd rather use gobject introspection and not schema generation) But the problem is not having a C API is using the current XML RPC API as it's base The current XML-RPC API contains a lot of decencies and inefficiencies and we would like to retire it as soon as we possibly can. Engine would like us to move to a message based API and 3rd parties want something simple like REST so it looks like no one actually wants to use XML-RPC. Not even us. I do think that having C supportability in our API is a good idea, but the current API should not be used as the base. The current API is irrelevant, we should focus on the API we will deliver for Fedora 18 / RHEL 7. I also really don't see what xmlrpc has to do with it. We specifically separated the transport from the API and the c bindings should have nothing to do with xmlrpc. - Original Message - From: Anthony Liguori anth...@codemonkey.ws To: VDSM Project Development vdsm-devel@lists.fedorahosted.org Cc: Adam Litke a...@us.ibm.com, Saggi Mizrahi smizr...@redhat.com Sent: Monday, June 25, 2012 10:18:33 AM Subject: [RFC] An alternative way to provide a supported interface -- libvdsm Hi, I've been reading through the API threads here and considering the options. To be honest, I worry a lot about the scope of these discussions and that there's a tremendous amount of work before we have a useful end result. I wonder if we can solve this problem by adding another layer of abstraction... As Adam is currently building a schema for VDSM's XML-RPC, we could use the QAPI code generators to build a libvdsm that provided a programmatic C interface for the XML-RPC interface. It would take some tweaking, but this could be made a supportable C interface. The rules for having a supportable C interface are basically: 1) Never change function signatures 2) Never remove functions 3) Always allocate structures in the library and/or pad 4) Only add to structures, never remove or reorder 5) Provide flags that default to zero to indicate that fields/features are not present. 6) Always zero-initialize structures Having a libvdsm would allow the transport to change over time w/o affecting end-users. There are lots of good tools for documenting C APIs and dealing with versioning of C APIs. While we can start out with a schema-generated API, over time, we can implement libvdsm in an open-coded fashion allowing old APIs to be reimplemented in terms of new APIs. From a compatibility perspective, libvdsm would be fully backwards compatible with old versions of VDSM (so it would keep XML-RPC support forever) but may require new versions of libvdsm to talk to new versions of VDSM. That would allow for APIs to be deprecated within VDSM without breaking old clients. I think this would be an incremental approach to building a supportable API today while still giving the flexibility to make changes in the long term. And it should be fairly easy to generate a JNI binding and also port ovirt-engine to use an interface like this (since it already uses the XML-RPC API). Regards, Anthony Liguori ___ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://fedorahosted.org/mailman/listinfo/vdsm-devel ___ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://fedorahosted.org/mailman/listinfo/vdsm-devel
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
On 06/27/2012 05:13 PM, Ayal Baron wrote: - Original Message - The idea of having a supported C API was something I was thinking about doing (But I'd rather use gobject introspection and not schema generation) But the problem is not having a C API is using the current XML RPC API as it's base The current XML-RPC API contains a lot of decencies and inefficiencies and we would like to retire it as soon as we possibly can. Engine would like us to move to a message based API and 3rd parties want something simple like REST so it looks like no one actually wants to use XML-RPC. Not even us. I do think that having C supportability in our API is a good idea, but the current API should not be used as the base. The current API is irrelevant, we should focus on the API we will deliver for Fedora 18 / RHEL 7. I also really don't see what xmlrpc has to do with it. We specifically separated the transport from the API and the c bindings should have nothing to do with xmlrpc. And I'm suggesting is to make the C bindings the supported interface and make the wire protocol an implementation detail. You could then implement the C bindings (using GObject or whatever) via the XML-RPC transport if you liked. It also presents a better integration story as you could more easily expose the VDSM API as part of a large CIM/AMQP model data model if you like. Regards, Anthony Liguori - Original Message - From: Anthony Liguorianth...@codemonkey.ws To: VDSM Project Developmentvdsm-devel@lists.fedorahosted.org Cc: Adam Litkea...@us.ibm.com, Saggi Mizrahi smizr...@redhat.com Sent: Monday, June 25, 2012 10:18:33 AM Subject: [RFC] An alternative way to provide a supported interface -- libvdsm Hi, I've been reading through the API threads here and considering the options. To be honest, I worry a lot about the scope of these discussions and that there's a tremendous amount of work before we have a useful end result. I wonder if we can solve this problem by adding another layer of abstraction... As Adam is currently building a schema for VDSM's XML-RPC, we could use the QAPI code generators to build a libvdsm that provided a programmatic C interface for the XML-RPC interface. It would take some tweaking, but this could be made a supportable C interface. The rules for having a supportable C interface are basically: 1) Never change function signatures 2) Never remove functions 3) Always allocate structures in the library and/or pad 4) Only add to structures, never remove or reorder 5) Provide flags that default to zero to indicate that fields/features are not present. 6) Always zero-initialize structures Having a libvdsm would allow the transport to change over time w/o affecting end-users. There are lots of good tools for documenting C APIs and dealing with versioning of C APIs. While we can start out with a schema-generated API, over time, we can implement libvdsm in an open-coded fashion allowing old APIs to be reimplemented in terms of new APIs. From a compatibility perspective, libvdsm would be fully backwards compatible with old versions of VDSM (so it would keep XML-RPC support forever) but may require new versions of libvdsm to talk to new versions of VDSM. That would allow for APIs to be deprecated within VDSM without breaking old clients. I think this would be an incremental approach to building a supportable API today while still giving the flexibility to make changes in the long term. And it should be fairly easy to generate a JNI binding and also port ovirt-engine to use an interface like this (since it already uses the XML-RPC API). Regards, Anthony Liguori ___ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://fedorahosted.org/mailman/listinfo/vdsm-devel ___ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://fedorahosted.org/mailman/listinfo/vdsm-devel
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
- Original Message - On 06/27/2012 05:13 PM, Ayal Baron wrote: - Original Message - The idea of having a supported C API was something I was thinking about doing (But I'd rather use gobject introspection and not schema generation) But the problem is not having a C API is using the current XML RPC API as it's base The current XML-RPC API contains a lot of decencies and inefficiencies and we would like to retire it as soon as we possibly can. Engine would like us to move to a message based API and 3rd parties want something simple like REST so it looks like no one actually wants to use XML-RPC. Not even us. I do think that having C supportability in our API is a good idea, but the current API should not be used as the base. The current API is irrelevant, we should focus on the API we will deliver for Fedora 18 / RHEL 7. I also really don't see what xmlrpc has to do with it. We specifically separated the transport from the API and the c bindings should have nothing to do with xmlrpc. And I'm suggesting is to make the C bindings the supported interface and make the wire protocol an implementation detail. You could then implement the C bindings (using GObject or whatever) via the XML-RPC transport if you liked. It also presents a better integration story as you could more easily expose the VDSM API as part of a large CIM/AMQP model data model if you like. Sounds good then. Your previous comment: From a compatibility perspective, libvdsm would be fully backwards compatible with old versions of VDSM (so it would keep XML-RPC support forever) Threw me off there as we would not want to keep on supporting XML-RPC. What's more, the current API has way too many things that have to go so needing to keep those would just be sad and painful. Regards, Anthony Liguori - Original Message - From: Anthony Liguorianth...@codemonkey.ws To: VDSM Project Developmentvdsm-devel@lists.fedorahosted.org Cc: Adam Litkea...@us.ibm.com, Saggi Mizrahi smizr...@redhat.com Sent: Monday, June 25, 2012 10:18:33 AM Subject: [RFC] An alternative way to provide a supported interface -- libvdsm Hi, I've been reading through the API threads here and considering the options. To be honest, I worry a lot about the scope of these discussions and that there's a tremendous amount of work before we have a useful end result. I wonder if we can solve this problem by adding another layer of abstraction... As Adam is currently building a schema for VDSM's XML-RPC, we could use the QAPI code generators to build a libvdsm that provided a programmatic C interface for the XML-RPC interface. It would take some tweaking, but this could be made a supportable C interface. The rules for having a supportable C interface are basically: 1) Never change function signatures 2) Never remove functions 3) Always allocate structures in the library and/or pad 4) Only add to structures, never remove or reorder 5) Provide flags that default to zero to indicate that fields/features are not present. 6) Always zero-initialize structures Having a libvdsm would allow the transport to change over time w/o affecting end-users. There are lots of good tools for documenting C APIs and dealing with versioning of C APIs. While we can start out with a schema-generated API, over time, we can implement libvdsm in an open-coded fashion allowing old APIs to be reimplemented in terms of new APIs. From a compatibility perspective, libvdsm would be fully backwards compatible with old versions of VDSM (so it would keep XML-RPC support forever) but may require new versions of libvdsm to talk to new versions of VDSM. That would allow for APIs to be deprecated within VDSM without breaking old clients. I think this would be an incremental approach to building a supportable API today while still giving the flexibility to make changes in the long term. And it should be fairly easy to generate a JNI binding and also port ovirt-engine to use an interface like this (since it already uses the XML-RPC API). Regards, Anthony Liguori ___ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://fedorahosted.org/mailman/listinfo/vdsm-devel ___ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://fedorahosted.org/mailman/listinfo/vdsm-devel
Re: [vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
On 06/27/2012 05:38 PM, Ayal Baron wrote: - Original Message - On 06/27/2012 05:13 PM, Ayal Baron wrote: - Original Message - The idea of having a supported C API was something I was thinking about doing (But I'd rather use gobject introspection and not schema generation) But the problem is not having a C API is using the current XML RPC API as it's base The current XML-RPC API contains a lot of decencies and inefficiencies and we would like to retire it as soon as we possibly can. Engine would like us to move to a message based API and 3rd parties want something simple like REST so it looks like no one actually wants to use XML-RPC. Not even us. I do think that having C supportability in our API is a good idea, but the current API should not be used as the base. The current API is irrelevant, we should focus on the API we will deliver for Fedora 18 / RHEL 7. I also really don't see what xmlrpc has to do with it. We specifically separated the transport from the API and the c bindings should have nothing to do with xmlrpc. And I'm suggesting is to make the C bindings the supported interface and make the wire protocol an implementation detail. You could then implement the C bindings (using GObject or whatever) via the XML-RPC transport if you liked. It also presents a better integration story as you could more easily expose the VDSM API as part of a large CIM/AMQP model data model if you like. Sounds good then. Your previous comment: From a compatibility perspective, libvdsm would be fully backwards compatible with old versions of VDSM (so it would keep XML-RPC support forever) Threw me off there as we would not want to keep on supporting XML-RPC. What's more, the current API has way too many things that have to go so needing to keep those would just be sad and painful. libvdsm would keep XML-RPC support--not VDSM itself. IOW, libvdsm would need enough XML-RPC support to talk to old versions of VDSM. That doesn't mean libvdsm needs to expose ever possible thing that's in the current XML-RPC interface. Regards, Anthony Liguori Regards, Anthony Liguori - Original Message - From: Anthony Liguorianth...@codemonkey.ws To: VDSM Project Developmentvdsm-devel@lists.fedorahosted.org Cc: Adam Litkea...@us.ibm.com, Saggi Mizrahi smizr...@redhat.com Sent: Monday, June 25, 2012 10:18:33 AM Subject: [RFC] An alternative way to provide a supported interface -- libvdsm Hi, I've been reading through the API threads here and considering the options. To be honest, I worry a lot about the scope of these discussions and that there's a tremendous amount of work before we have a useful end result. I wonder if we can solve this problem by adding another layer of abstraction... As Adam is currently building a schema for VDSM's XML-RPC, we could use the QAPI code generators to build a libvdsm that provided a programmatic C interface for the XML-RPC interface. It would take some tweaking, but this could be made a supportable C interface. The rules for having a supportable C interface are basically: 1) Never change function signatures 2) Never remove functions 3) Always allocate structures in the library and/or pad 4) Only add to structures, never remove or reorder 5) Provide flags that default to zero to indicate that fields/features are not present. 6) Always zero-initialize structures Having a libvdsm would allow the transport to change over time w/o affecting end-users. There are lots of good tools for documenting C APIs and dealing with versioning of C APIs. While we can start out with a schema-generated API, over time, we can implement libvdsm in an open-coded fashion allowing old APIs to be reimplemented in terms of new APIs. From a compatibility perspective, libvdsm would be fully backwards compatible with old versions of VDSM (so it would keep XML-RPC support forever) but may require new versions of libvdsm to talk to new versions of VDSM. That would allow for APIs to be deprecated within VDSM without breaking old clients. I think this would be an incremental approach to building a supportable API today while still giving the flexibility to make changes in the long term. And it should be fairly easy to generate a JNI binding and also port ovirt-engine to use an interface like this (since it already uses the XML-RPC API). Regards, Anthony Liguori ___ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://fedorahosted.org/mailman/listinfo/vdsm-devel ___ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://fedorahosted.org/mailman/listinfo/vdsm-devel
[vdsm] [RFC] An alternative way to provide a supported interface -- libvdsm
Hi, I've been reading through the API threads here and considering the options. To be honest, I worry a lot about the scope of these discussions and that there's a tremendous amount of work before we have a useful end result. I wonder if we can solve this problem by adding another layer of abstraction... As Adam is currently building a schema for VDSM's XML-RPC, we could use the QAPI code generators to build a libvdsm that provided a programmatic C interface for the XML-RPC interface. It would take some tweaking, but this could be made a supportable C interface. The rules for having a supportable C interface are basically: 1) Never change function signatures 2) Never remove functions 3) Always allocate structures in the library and/or pad 4) Only add to structures, never remove or reorder 5) Provide flags that default to zero to indicate that fields/features are not present. 6) Always zero-initialize structures Having a libvdsm would allow the transport to change over time w/o affecting end-users. There are lots of good tools for documenting C APIs and dealing with versioning of C APIs. While we can start out with a schema-generated API, over time, we can implement libvdsm in an open-coded fashion allowing old APIs to be reimplemented in terms of new APIs. From a compatibility perspective, libvdsm would be fully backwards compatible with old versions of VDSM (so it would keep XML-RPC support forever) but may require new versions of libvdsm to talk to new versions of VDSM. That would allow for APIs to be deprecated within VDSM without breaking old clients. I think this would be an incremental approach to building a supportable API today while still giving the flexibility to make changes in the long term. And it should be fairly easy to generate a JNI binding and also port ovirt-engine to use an interface like this (since it already uses the XML-RPC API). Regards, Anthony Liguori ___ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://fedorahosted.org/mailman/listinfo/vdsm-devel
