[ClusterLabs] FR: send failcount to OCF RA start/stop actions

[Ken Gaillot]

On 05/09/2016 06:36 PM, Jehan-Guillaume de Rorthais wrote:
> Le Mon, 9 May 2016 17:40:19 -0500,
> Ken Gaillot <kgaillot at redhat.com> a écrit :
> 
>> On 05/04/2016 11:47 AM, Adam Spiers wrote:
>>> Ken Gaillot <kgaillot at redhat.com> wrote:
>>>> On 05/04/2016 08:49 AM, Klaus Wenninger wrote:
>>>>> On 05/04/2016 02:09 PM, Adam Spiers wrote:
>>>>>> Hi all,
>>>>>>
>>>>>> As discussed with Ken and Andrew at the OpenStack summit last week, we
>>>>>> would like Pacemaker to be extended to export the current failcount as
>>>>>> an environment variable to OCF RA scripts when they are invoked with
>>>>>> 'start' or 'stop' actions.  This would mean that if you have
>>>>>> start-failure-is-fatal=false and migration-threshold=3 (say), then you
>>>>>> would be able to implement a different behaviour for the third and
>>>>>> final 'stop' of a service executed on a node, which is different to
>>>>>> the previous 'stop' actions executed just prior to attempting a
>>>>>> restart of the service.  (In the non-clone case, this would happen
>>>>>> just before migrating the service to another node.)
>>>>> So what you actually want to know is how much headroom
>>>>> there still is till the resource would be migrated.
>>>>> So wouldn't it then be much more catchy if we don't pass
>>>>> the failcount but rather the headroom?
>>>>
>>>> Yes, that's the plan: pass a new environment variable with
>>>> (migration-threshold - fail-count) when recovering a resource. I haven't
>>>> worked out the exact behavior yet, but that's the idea. I do hope to get
>>>> this in 1.1.15 since it's a small change.
>>>>
>>>> The advantage over using crm_failcount is that it will be limited to the
>>>> current recovery attempt, and it will calculate the headroom as you say,
>>>> rather than the raw failcount.
>>>
>>> Headroom sounds more usable, but if it's not significant extra work,
>>> why not pass both?  It could come in handy, even if only for more
>>> informative logging from the RA.
>>>
>>> Thanks a lot!
>>
>> Here is what I'm testing currently:
>>
>> - When the cluster recovers a resource, the resource agent's stop action
>> will get a new variable, OCF_RESKEY_CRM_meta_recovery_left =
>> migration-threshold - fail-count on the local node.
>>
>> - The variable is not added for any action other than stop.
> 
> If the resource is a multistate one, the recover action will do a
> demote->stop->start->promote. What if the failure occurs during the first
> demote call and a new transition will try to demote first again? I suppose this
> new variable should appears at least in demote and stop action to cover such
> situation, isn't it?

Good question. I can easily imagine a "lightweight stop", but I can't
think of a practical use for a "lightweight demote". If someone has a
scenario where that would be useful, I can look at adding it.