[ClusterLabs] Informing RAs about recovery: failed resource recovery, or any start-stop cycle?

[Andrew Beekhof]

On Tue, Jun 7, 2016 at 8:29 AM, Adam Spiers <aspiers at suse.com> wrote:
> Ken Gaillot <kgaillot at redhat.com> wrote:
>> On 06/02/2016 08:01 PM, Andrew Beekhof wrote:
>> > On Fri, May 20, 2016 at 1:53 AM, Ken Gaillot <kgaillot at redhat.com> wrote:
>> >> A recent thread discussed a proposed new feature, a new environment
>> >> variable that would be passed to resource agents, indicating whether a
>> >> stop action was part of a recovery.
>> >>
>> >> Since that thread was long and covered a lot of topics, I'm starting a
>> >> new one to focus on the core issue remaining:
>> >>
>> >> The original idea was to pass the number of restarts remaining before
>> >> the resource will no longer tried to be started on the same node. This
>> >> involves calculating (fail-count - migration-threshold), and that
>> >> implies certain limitations: (1) it will only be set when the cluster
>> >> checks migration-threshold; (2) it will only be set for the failed
>> >> resource itself, not for other resources that may be recovered due to
>> >> dependencies on it.
>> >>
>> >> Ulrich Windl proposed an alternative: setting a boolean value instead. I
>> >> forgot to cc the list on my reply, so I'll summarize now: We would set a
>> >> new variable like OCF_RESKEY_CRM_recovery=true
>> >
>> > This concept worries me, especially when what we've implemented is
>> > called OCF_RESKEY_CRM_restarting.
>>
>> Agreed; I plan to rename it yet again, to OCF_RESKEY_CRM_start_expected.
>
> [snipped]
>
>> My main question is how useful would it actually be in the proposed use
>> cases. Considering the possibility that the expected start might never
>> happen (or fail), can an RA really do anything different if
>> start_expected=true?
>
> That's the wrong question :-)
>
>> If the use case is there, I have no problem with
>> adding it, but I want to make sure it's worthwhile.
>
> The use case which started this whole thread is for
> start_expected=false, not start_expected=true.

Isn't this just two sides of the same coin?
If you're not doing the same thing for both cases, then you're just
reversing the order of the clauses.

"A isn't different from B, B is different from A!" :-)

> When it's false for
> NovaCompute, we call nova service-disable to ensure that nova doesn't
> attempt to schedule any more VMs on that host.
>
> If start_expected=true, we don't *want* to do anything different.  So
> it doesn't matter even if the expected start never happens.