Open Stack

Parallel worker was what I initially thought. But what to do if the engine hosting that worker goes down?

-Vishnu

From: Angus Salkeld [mailto:asalkeld at mirantis.com]
Sent: Thursday, November 13, 2014 5:22 PM
To: OpenStack Development Mailing List (not for usage questions)
Subject: Re: [openstack-dev] [Heat] Using Job Queues for timeout ops

On Thu, Nov 13, 2014 at 6:29 PM, Murugan, Visnusaran <visnusaran.murugan at hp.com<mailto:visnusaran.murugan at hp.com>> wrote:
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)
We will shortly have a worker job, can't we have a job that just sleeps that gets started in parallel with the job that is doing the work?
It gets to the end of the sleep and runs a check.

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


My suggestion above could catch failures as long as it was run in a different process.
-Angus


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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