Hello Shuva,
Comments inline
Thanks
Prasanna
From: Shuva Kar [mailto:[email protected]]
Sent: Tuesday, June 06, 2017 10:29 AM
To: Prasanna Huddar <[email protected]>
Cc: Luis Gomez <[email protected]>; Kanagasundaram K
<[email protected]>; [email protected]
Subject: Re: [openflowplugin-dev] Proposed Reconciliation framework
Sorry for missing out completely on this thread :)
Have a few queries for your model,Prasanna, from my end :
1. When you say "vendors" you do mean applications right? If that is so you
would still require a prioritised execution of the tasks for each of the
applications. The apps would register themselves at a particular priority and
submit their task when the come-up. All the framework does is to take care of
executing these tasks.
Am i correct?
[Prasanna]:
Applications or Vendors defined Resync algorithm.
Prioritized execution is again dependent on the Custom algorithm.
1. Vendor “A” may opt for prioritized execution(Resync), in that case he
will register one Resync application in which he will give prioritization
provide required functionality.
2. Vendor “B” is not bothered about prioritization he just wants to push
certain groups and flows down.
3. The framework gives option to plug in the custom algorithms, without
getting into the implementation details of Resync.
2. Now we would have (in the future :)) tasks that depend on each other- like
ports coming up --> groups pushed on them and flows pointing to them, a typical
tunnelling flow? how would your framework handle such tasks?
[Prasanna]:
As discussed yesterday the framework waits for certain time for application to
tell the status back.
1. Application which are participating in Reconciliation will anyway
handle port up / down separately.
3. How do you define end of a task? Since "some" tasks that are network
resource dependent is a function of time. Now you might say we can wait for a
predefined amount of time, but that is a very very poor design and is a can of
worms and a pandorica of Heisenbugs
[Prasanna]:
What are the issues you see? because we are giving the option for
application to inform back the status of reconciliation?
If they do not inform during certain amount of time than we timeout.
If you can suggest any better approach, please do.
Even OF uses timeouts for connection monitoring.
4. I donot like the idea of a switch disconnect when resync fails - what is a
resync failure ? flows/groups/meters not getting pushed for a particular device
, if thats so the applications should be designed to take care of failures.
Ideally, the framework should have hooks for applications to register for
failures and errors.
[Prasanna]:
The whole concept is if the resync fails the switch is in unknown state,
and for sure we do not want application to have access to a switch which is in
unknown state.
Current design just does not take care of the situation where Reconciliation
fails, application continues using it even though some flows are missing, which
is still a bad state.
If any UC comes where application can selfheal from unknown switch state, using
some kind intelligence than we might need to enhance the said infrastructure,
which can be done beyond Nitrogen.
5. This model of reconciliation encourages the applications to be responsible
of their own data, hope we are making a conscious choice.
[Prasanna]: Yes, plugin should not be worried about application data.
6. Applications should take of group-> flow, group-group dependencies and not
the framework. The FRM/FRS shall be the last piece or default task that runs
for applications that are poor enough to run separate reconciliation tasks.
[Prasanna]:
Infrastructure does not get into these details.
My 2 cents here, given that the problem definition here is to have a
well-defined and well-tracked FSM of a switch that is unknown to one that has
been reconcile, it would be grat if we address that first.Also, let's not push
code before the design has been finalised, else we would end up with tonnes of
bugs from a new feature perspective.
[Prasanna]:
- FSM enhancement can happen in parallel and be plugged in into this
infra, and since we are moving towards bundles based resync.
- This design is in the community for review, please do review on
priority, since this is targeted for Nitrogen release.
- We can plan for design review, once we agree on the Design published.
Br,shuva
On Tue, May 16, 2017 at 10:37 AM, Prasanna Huddar
<[email protected]<mailto:[email protected]>> wrote:
Hello Luis,
Agree, that’s why the framework, the framework just defines how
reconciliation call flow should happen, but does not define an algorithm.
Vendors can plug-in their Reconciliation algorithm as needed into the framework
Thanks
Prasanna
From: Luis Gomez [mailto:[email protected]<mailto:[email protected]>]
Sent: Wednesday, May 10, 2017 10:38 PM
To: Prasanna Huddar
<[email protected]<mailto:[email protected]>>
Cc: Anil Vishnoi <[email protected]<mailto:[email protected]>>; Abhijit
Kumbhare <[email protected]<mailto:[email protected]>>;
[email protected]<mailto:[email protected]>;
Kanagasundaram K
<[email protected]<mailto:[email protected]>>
Subject: Re: [openflowplugin-dev] Proposed Reconciliation framework
I think the main point here is there is no unique way of doing reconciliation
and different applications may also have different requirements on this, for
example:
- Some application may wipe out all switch data in DS when switch goes down so
they can replay everything when switch reconnects. In this case reconciliation
is as simple as sending a delete all when switch connects.
- Some applications may delete flows but keep groups and meters when switch is
down, so they only need to replay flows after switch reconnects. In this case
reconciliation just need to synchronize groups/meters when switch connects.
- Some applications may react as "nothing happens" when switch goes down so
they expect the reconciliation to do all the work of synchronizing
flows/groups/meters.
Unless we can get a very "smart" reconciliation module that can take care of
every possible scenario in an optimal way, I agree we need a framework to let
applications do the reconciliation.
BR/Luis
On May 10, 2017, at 8:35 AM, Prasanna Huddar
<[email protected]<mailto:[email protected]>> wrote:
Hello All,
If you have any more comments, please share.
Thanks
Prasanna
From: Prasanna Huddar
Sent: Friday, March 03, 2017 3:37 PM
To: Anil Vishnoi <[email protected]<mailto:[email protected]>>; Abhijit
Kumbhare <[email protected]<mailto:[email protected]>>
Cc:
[email protected]<mailto:[email protected]>;
Kanagasundaram K
<[email protected]<mailto:[email protected]>>
Subject: RE: [openflowplugin-dev] Proposed Reconciliation framework
Hello Anil,
My inputs inline below
Thanks,
Prasanna
From: Anil Vishnoi [mailto:[email protected]]
Sent: 02 March 2017 13:22
To: Abhijit Kumbhare <[email protected]<mailto:[email protected]>>
Cc: Prasanna Huddar
<[email protected]<mailto:[email protected]>>;
[email protected]<mailto:[email protected]>;
Kanagasundaram K
<[email protected]<mailto:[email protected]>>
Subject: Re: [openflowplugin-dev] Proposed Reconciliation framework
Hi Prasanna,
I liked the idea of notifying the applications once the node is reconciled and
ready for further configuration. I have few questions about the proposed
framework in the context of single node + current master-slave implementation:
(1) I think following is not the case, for sure not for FRM, and i believe for
FRM-Sync as well
Slide-4:
"If Reconciliation fails the ODL disconnects the switch, and the whole process
is repeated by Re-sync and application
Applications start acting on OF switch which is in “unknown” state, which
should be avoided."
[Prasanna]: Ok, Will reword/ update. If Re-sync fails only options is
reconnect the switch.
(2) Slide-8:
"Application(s) registering with Reconciliation module is encouraged since:
Applications would know the right Flows and group which needs to be replayed
with write operation(Add / delete / update).
FRM / FRS would not have application view of flows / group, it would blindly
replay the flows / groups.
Also flows having idle / hard timeout can be gracefully handled by application
rather than FRM / FRS."
Are we assuming the application won't maintain the correct configuration in the
data store ?
[Prasanna]:
No, FRM / FRS would have the right information in data-store, but FRM / FRS
will push all the flows blindly, whereas application can push optimized set of
flows, as covered in couple of points below.
I believe meter and group always need to be programmed before flow, so is there
any other variance of ordering where we want application to do the
reconciliation ?
[Prasanna]:
Yes, once FRM / FRS or application registers with Reconciliation module,
the algorithm implemented by application can handle all these variances,
algorithm related info are just reccomendations.
If the flows are installed with idle/hard timeout, we should expect application
to remove it from data store. Unfortunately data store can't help much here, so
application will have to take this burden.
[Prasanna]:
Agree, but some flow timeouts can happen when Switch is Disconnected from
switch, timeout information is available only in application, using this info
application can re-program the flows as part of re-sync or exclude it.
So we really keep the clear contract with respect to data store, i don't really
see any reason, why we should leave the node reconciliation to application.
Plugin should do the reconciliation based on the config state in the data store
and once it's done with that reconciliation, it can notify application to
reconcile it's business logic.
Also in case of controller restart, the only state application will have is in
config data store, and until and unless they run their business logic they
can't figure out the correct ordering. And they can't run the business logic
because there is no node advertized to them yet.
[Prasanna]:
Regarding Plugin implementing the Reconciliation;
Agree, but plugin should run it as separate bundle, which would be enabled
/ disabled through flag.
1. Since, OVS might support Bundles , but community plugin cannot accept
all other users to use OVS.
a. So, we need to give them option to use their own algorithm(separate
bundle)
b. If future a better algorithm comes up user should be able to move to
it without dependencies.
c. Reconciliation framework infra should work irrespective of
Reconciliation algorithm.
Regarding node advertisement:
1. Agree, node is not advertised to application.
2. But as part of Reconciliation call-back / notification, reconciliation
framework calls the call back function or notification with switch information.
a. This switch information can be used by application to decide which
flows has to be re-programmed.
i.
Timer is one option to filter out flows.
(3) If we leave the reconciliation to the applications, and assume that two
applications are using the same node, do we expect that both the application
will have to use the similar kind of reconciliation mechanism? Assuming one
wants to use bundle or one want to use the vanilla reconciliation mechanism
that we have? If not, who will win? If yes, how we will implement it at the
plugin level, because bundle's like features are provided at the plugin level.
So basically i don't see how you can implement different reconciliation methods
without depending on the plugin. I can see that you can use one method for
reconciling specific node, but then all the application using that node need to
use the same method. By doing that we are basically pushing switch specific
reconciliation to the application level, and in my opinion that's not a good
idea.
[Prasanna]:
We are completely dependent on plugin for all the contracts to
push the flows(meter/flows/groups/etc) down to the switch.
That is why we say Plugin registers with RPC than invokes Reconciliation
framework.
We do not accept the application to use the same method, but
anything related to algorithm are just recommendation by this framework.
Scenario;
1. Consider App1 and App2 have registered to Reconciliation framework.
2. Plugin gives different contracts to program
flows(flows/group/meter/etc).
a. General flows.
b. Flows with barrier message.
c. Flows using bundles.
3. App1 and App2 can use any construct of plugin to program the flows.
We can discuss this more if needed in one of the upcoming calls.
(4) slide-9
"Check if Reconciliation is needed, if yes, update the DS status of the Switch
and go to Step 6"
Given that switch is not yet in data store, what really we want to update in
the data store? Also i didn't find the step 6 in the slides.
[Prasanna]
“ Given that switch is not yet in data store, what really we want to update in
the data store? Also i didn't find the step 6 in the slides.”
Typo will be corrected, no DS reference is needed
Sorry, Updated the slide just check, no idea with gdrive conversions.
(5) slide-10
"9.Application(s) would also wait for error from switch, for pre-defined time."
Why do we need to wait for pre-define time?, given that the current API-s do
return the future and future will fail if the configuration on switch fails.
[Prasanna]:
Ah, than not needed.
(6) slide -10
"10.Application(s) would inform the Reconciliation status to Reconciliation
module."
How long does plugin wait on the application to notify?
[Prasanna]:
We can make it configurable.
(7) Proposal says that if any of the application is not able to reconcile
successfully, it should disconnect the device. Assume out of 2 application, one
application is able to reconcile and other one failed, how do disconnecting the
switch will help here ? is there any scenario where we expect different outcome
once switch re-connect?
[Prasanna]:
Are you suggesting:
When Reconciliation fails, whether to disconnect or not should be left to
solution?
- Is yes, agree.
(8) If we push the node reconciliation to applications, are we assuming that
they will use the RPC for flow installation during the reconciliation ?
[Prasanna]:
Yes, we are registering the RPC methods with before invoking the
Reconciliation framework.
But this is not hard requirement, again this is just framework, which should be
flexible for future needs.
We can discuss further in one of the calls after Carbon release(or separate
call early, since Carbon is on priority), which is round the corner.
Thanks
Anil
On Wed, Feb 22, 2017 at 9:34 AM, Abhijit Kumbhare
<[email protected]<mailto:[email protected]>> wrote:
Just to clarify - this reconciliation workflow as well as bundles based
reconciliation being discussed is for the next release (Nitrogen) and not part
of Carbon. The basic bundles support can be code reviewed & merged as it is a
stretch goal item in the Carbon release plan - however it will not be used by
reconciliation or any other application in Carbon.
On Wed, Feb 22, 2017 at 4:35 AM, Prasanna Huddar
<[email protected]<mailto:[email protected]>> wrote:
Hello All,
Please review the proposed new Reconciliation workflow and provide your
inputs.
Link to the document(1st
draft):https://wiki.opendaylight.org/view/OpenDaylight_OpenFlow_Plugin:Reconciliation#Future_Enhancements
Thanks,
Prasanna
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Thanks
Anil
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