Le 22/12/2014 13:37, Alex Xu a écrit :


2014-12-22 10:36 GMT+08:00 Lingxian Kong <anlin.k...@gmail.com <mailto:anlin.k...@gmail.com>>:

    2014-12-22 9:21 GMT+08:00 Alex Xu <sou...@gmail.com
    <mailto:sou...@gmail.com>>:
    >
    >
    > 2014-12-22 9:01 GMT+08:00 Lingxian Kong <anlin.k...@gmail.com
    <mailto:anlin.k...@gmail.com>>:
    >>

    >>
    >> but what if the compute node is back to normal? There will be
    >> instances in the same server group with affinity policy, but
    located
    >> in different hosts.
    >>
    >
    > If operator decide to evacuate the instance from the failed
    host, we should
    > fence the failed host first.

    Yes, actually. I mean the recommandation or prerequisite should be
    emphasized somewhere, e.g. the Operation Guide, otherwise it'll make
    things more confused. But the issue you are working around is indeed a
    problem we should solve.


Yea, you are right, we should doc it if we think this make sense. Thanks!

As I said, I'm not in favor of adding more complexity in the instance group setup that is done in the conductor for basic race condition reasons.

If I understand correctly, the problem is when there is only one host for all the instances belonging to a group with affinity filter and this host is down, then the filter will deny any other host and consequently the request will fail while it should succeed.

Is this really a problem ? I mean, it appears to me that's a normal behaviour because a filter is by definition an *hard* policy.

So, provided you would like to implement *soft* policies, that sounds more likely a *weigher* that you would like to have : ie. make sure that hosts running existing instances in the group are weighted more than other ones so they'll be chosen every time, but in case they're down, allow the scheduler to pick other hosts.

HTH,
-Sylvain




    --
    Regards!
    -----------------------------------
    Lingxian Kong

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