Hi all,

Convergence-POC distributes stack operations by sending resource actions over 
RPC for any heat-engine to execute. Entire stack lifecycle will be controlled 
by worker/observer notifications. This distributed model has its own advantages 
and disadvantages.

Any stack operation has a timeout and a single engine will be responsible for 
it. If that engine goes down, timeout is lost along with it. So a traditional 
way is for other engines to recreate timeout from scratch. Also a missed 
resource action notification will be detected only when stack operation timeout 
happens.

To overcome this, we will need the following capability:

1.       Resource timeout (can be used for retry)

2.       Recover from engine failure (loss of stack timeout, resource action 
notification)


Suggestion:

1.       Use task queue like celery to host timeouts for both stack and 
resource.

2.       Poll database for engine failures and restart timers/ retrigger 
resource retry (IMHO: This would be a traditional and weighs heavy)

3.       Migrate heat to use TaskFlow. (Too many code change)

I am not suggesting we use Task Flow. Using celery will have very minimum code 
change. (decorate appropriate functions)


Your thoughts.

-Vishnu
IRC: ckmvishnu
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