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From Chiradeep Vittal <Chiradeep.Vit...@citrix.com>
Subject Re: HA is broken on master
Date Wed, 02 Oct 2013 23:09:57 GMT
Perhaps as a result of this work:
https://cwiki.apache.org/confluence/x/tYvlAQ
I think Kelven is trying to separate the job state (starting, stopping)
from the actual VM state.

On 10/2/13 3:36 PM, "Darren Shepherd" <darren.s.shepherd@gmail.com> wrote:

>Alex,
>
>In scheduleRestart() when it calls _itMgr.advanceStop() it used to
>pass the VO.  Now it passes a UUID.  So the VO the HA manager holds is
>out of sync with the DB and the recorded previous state and update
>count are wrong, so HA will just stop the VM in the worker.
>
>I really think the update count approach is far too fragile.  For
>example, currently if you try to start a VM and it fails, the update
>count will change.  But the current code will record the new update
>count so the next try it will have the updated count.  I can see the
>following issue, maybe there's some work around for it.  Imagine you
>have a large failure, the stuff really hits the fan.  So you have
>1000's of HA jobs trying to run and things just keep failing.  So to
>stop the churn you shutdown the mgmt stack to figure out whats up with
>infrastructure.  There's a really good chance that you would kill the
>mgmt stack while a VM was in starting.  So now the hawork update count
>will be out of sync with the current DB.  So when you bring the mgmt
>stack back up.  It won't try to restart that VM.
>
>Maybe that situation is taken care of somehow, but I could probably
>dream up another one.  I think it is far simpler that when a user
>starts a VM, you record in the vm_instance table, in a new column,
>"Should be running", then when the HA worker processes the record, it
>will always say it should be running.  If the user does a stop, you
>clear that column.  This has the added benefit of when things are bad
>and a user starts clicking restart/start, they won't mess with the HA.
> I think, maybe things have changed, but before what I would see is
>that we'd have an issue so VMs should be started, but weren't.  So HA
>was trying, but it kept failing.  The user would login and see they're
>VM is down, so they would click start.  But that would fail (similar
>to how HA was also failing).  So the VM would stay in stopped, but
>since they touched the VM, the update count changed and HA wouldn't
>start it back up when the infra worked again.  So customers who
>proactively tried to do something would get penalized in that their
>downtime was longer because cloudstack wouldn't bring their VM back up
>like the other VMs.
>
>Darren


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