On Mon, Feb 9, 2009 at 13:31, Jean-Baptiste Onofré <[email protected]> wrote: > Hi Guillaume, > > If I have right understood, the ClusterRegistration in the registry provides > a filter. After that, the user needs to define if the endpoint is "member" of > the cluster or not. It means that, in a cluster, we can have : > - standalone endpoints (dealing only with the local SMX instance) > - clustered endpoints (dealing with all SMX cluster members). Does it mean > that this kind of endpoints are federate in all cluster members (the endpoint > is present in all cluster member) ?
The ClusterRegistration provides a filter that will match an endpoint set. If the endpoint that created and sent the exchange matches, the exchanges will be re-routed. In such case, the cluster engine will send a JMS message, that will be consumed by another cluster engine. The consumption is based on JMS selectors, so it will only consume messages that will be transformed into a JBI exchange, which target endpoint exists locally. So you can achieve both load-balancing and remoting. Let's take a real example: HTTP consumer -> EIP routing slip -> (xslt transformation , HTTP provider, xslt transformation) This route defines a transformation on the request, send it to another web service, and transform the response back. If you configure the HTTP consumer to be "clustered", then, it will look somewhat like: HTTP -> JMS -> EIP If you deploy this whole application on two instances (assuming the underlying JMS brokers are connected together), an http request coming to the first smx instance could be processed (eip and the remaining of the flow) by another instance (load-balancing / some failover). You could also imagine deploying the HTTP consumer only on one instance, and the remaining of the application only on a second instance (remoting). > If I compare with application servers clustering (with the EJBs session > replication, entity turns, etc), when you setup the application server in > cluster mode, your application works in cluster mode (you can't choose if > it's cluster compliant or not). Using JBoss Groups, you can register > applications in cluster or not. > > Maybe it can be interesting to let the user to choose which endpoints is > cluster one or not with something like, defining a ClusterRegistration > service that store the cluster endpoints set. Like this, we can manage OSGi > and JBI packaging, implicit cluster and manual cluster. But the user needs to > define clustered endpoint. Not sure if we can really compare with app servers clustering. If you want true clustering, you need to make sure the whole state can failed over onto another node. Unfortunately, most of the components maintain some state. For example if an endpoint receives an exchange and create a copy of it to send it to another endpoint, wait for the response and then copy it as the response of the original exchange, this original exchange if smx crashes unless it is stored somewhere. The servicemix-eip component has a configurable storage that is used to store all such data. It defaults to an simple map without persistence, but you can configure if to use a database if you want. However, this downgrades performances a lot. Usually, the best way is to put a single cluster endpoint for a whole flow at the beginning of this flow. In our example above, clustering the HTTP consumer should be somewhat sufficient: if the something wrong happens when processing the eip, xslt transformations or the call to the other web service, the transaction can be rolled back and retried on another smx instance. However, if the http client is waiting for a response and the first smx instance (hosting the http consumer) crashes, there's really nothing we can do ... Anyway, an interesting option would be to have a more complex filter that automatically detects exchanges that need to be clustered if for a given flow, no exchange have gone through the cluster engine yet. It would automatically cluster all consumer endpoints, but not subsequent exchanges. > > It's only a quick think about SMX cluster. The topic is very interesting. > > Regards > JB > > On Mon 09/02/09 09:28, "Guillaume Nodet" [email protected] wrote: >> I've commited my ongoing work about servicemix 4 clustering at >> https://svn.apache.org/repos/asf/servicemix/smx4/nmr/trunk/jbi/ >> cluster/ > It's not in the build yet and I committed it for discussion purpose. >> >> This work has two goals: >> * provide some persistence in the JBI layer >> * provide some transparent remoting between JBI endpoints >> >> The way I've began implementing that is to use an ExchangeListener in >> the NMR to re-route exchanges to a cluster endpoint (I guess it should >> be renamed to something like "cluster engine" to avoid being confused >> with "clustered endpoints"). >> >> The org.apache.servicemix.cluster.requestor package dervies from the >> spring message listener container and implements a jms layer which is >> able to provide request / response in an asynchronous way. >> >> I've experimented different things, and the one i've been focusing >> lately > is to use a single JMS queue and selectors. Let me explain a bit. >> The JMS flow in servicemix 3 was using lots of different destinations >> (one per container + one per endpoint + one per service qname + one >> per > interface qname). The problem with such a design is that a jms >> consumer > can easily consume only from one destination (unless we use some >> specific > activemq features). Another problem is that if not using activemq, >> setting up lots of JMS destinations can be really tedious. The use of >> a > single destination leads to fewer consumers, at the expense of using >> jms > selectors. Previsouly, i've tried to use two queues (one for >> requests > and another one for responses) but there's no real benefits in doing >> this > imho. >> >> The other thing i've been focusing on is to make sure that processing >> a > jms message does not block a thread, and yet be able to use jms or xa >> transactions. This is not so easy. For example the spring jms >> listener > containers do use a thread for consuming the jms message and process >> it, > expecting the processing to happen synchronously. However, in >> servicemix > synchronous processing is a bad idea, as if it involves sending an >> http > request and waiting for a response, this means blocking a thread for >> nothing. > For scalability, we need to not block threads if possible. But spring >> message listener containers only support synchronous processing, so >> I've > hacked two new containers, one being JMS compliant, and another one >> specific > to ActiveMQ which is much more performant. It uses a >> MessageAvailableListener > to be notified when consumers have messages to be processed instead of >> wasting > threads to poll actively for messages. >> Anyway, both containers can support client ack, jms local transactions >> or > xa transactions in asynchronous mode. >> >> I haven't really worked on how to register such endpoints (from the >> user point of >> view). At the moment, we need to register a ClusterRegistration in the >> OSGi > registry. Such registrations contains a filter that will be used to >> decide if a >> new active / consumer exchange should be re-routed to the cluster engine or >> not. > The most simple filter would be a filter that checks the source endpoint >> and > will thus cluster all exchanges outgoing from a given endpoint. >> As for how to register such objects, one way would be to put that on >> the endpoint >> exporter that is used in smx4 to register jbi endpoints with the OSGi >> packaging, > but this would not work with JBI packaging (such registrations would have >> to be > deployed in a separate osgi bundle). I was also thinking about adding a >> simple > boolean property on all endpoints, something like clustered="true". >> >> Sorry for the long rant, but I should have sent this email way earlier >> ... > Feedback welcome. >> >> >> >> -- >> Cheers, >> Guillaume Nodet >> ------------------------ >> Blog: http://gnodet.blogspot.com/ > ------------------------ >> Open Source SOA >> http://fusesource.com >> >> > > -- Cheers, Guillaume Nodet ------------------------ Blog: http://gnodet.blogspot.com/ ------------------------ Open Source SOA http://fusesource.com
