[ClusterLabs] Antw: [EXT] Re: resource management of standby node

[Andrei Borzenkov]

30.11.2020 17:05, Ulrich Windl пишет:
>>>> Andrei Borzenkov <arvidjaar at gmail.com> schrieb am 30.11.2020 um 14:18 in
> Nachricht
> <CAA91j0XLfztbSmCkDGM0Ofb2FBKCquwyhiEU8LV5WgiUU3H=iA at mail.gmail.com>:
>> On Mon, Nov 30, 2020 at 3:11 PM Ulrich Windl
>> <Ulrich.Windl at rz.uni‑regensburg.de> wrote:
>>>
>>> Hi!
>>>
>>> In SLES15 I'm surprised what a standby node does: My guess was that a 
>> standby node would stop all resources and then just "shut up", but it seems
> 
>> it still tried to place resources and calls monitor operations.
>>>
>>
>> Standby nodes are ineligible for running resources. It does not stop
>> pacemaker from trying to place resources somewhere in cluster.
> 
> But it's somewhat ridiculous if all nodes are in standby.
> 

If you do not want cluster to manager resources, put cluster in
maintenance mode.

>>
>>> Like this after a configuration change:
>>> pacemaker‑controld[49413]:  notice: Result of probe operation for 
>> prm_test_raid_md1 on h18: not running
>>>
>>
>> Probe is not monitor. Normally it happens once when the pacemaker is
>> started. It should not really be affected by putting node in standby.
> 
> A configuration change triggered it. Again: It makes little sense if all nodes
> are in standby: What action would be performed depending on the result of the
> probe? None, I guess; so why probe?
> 

I guess because you are using standby node in different way than it was
designed for. It really is intended for graceful isolating of single
node, not to stop resource management throughout the whole cluster.

>>
>>> Or this (on the DC node):
>>> pacemaker‑schedulerd[69599]:  notice: Cannot pair prm_test_raid_md1:0 with
> 
>> instance of cln_DLM
>>>
>>
>> So? As mentioned, pacemaker still attempts to manage resources, it
>> just excludes standby nodes from the list of possible candidates. If
> 
> Buit there are no (zero) candidates!
> 

If there is workflow that can only be implemented by putting all nodes
in standby then I guess this optimization could be implemented. So far
it is not clear, are you complaining about log entries or did you
experience real problem? I have a feeling that everything worked for you
but you are annoyed by seeing log entries that you did not expect.

>> all nodes are in standby mode, no resource can run anywhere, but
>> pacemaker still needs to try placing resources to see it. Maybe you
>> really want cluster maintenance mode instead.
> 
> I thought about that:
> First put all nodes in standby to stop resources, then put all nodes in
> maintenance mode, then edit configuration.

There is no maintenance mode for a single node.

> Then turn off maintenance mode for all nodes, then put them online again.
> 
> Soounds somewhat complicated.
> 

Put cluster in maintenance, edit configuration, exit maintenance mode.
You do not need to stop resources as long as new configuration will have
the same resources under different names. They can remain active,
pacemaker will probe and discover them when existing maintenance mode.

>>
>>> Maybe I should have done differently, but after a test setup I noticed that
> 
>> I named by primitives in a non‑consistent way, and wanted to mass‑rename 
>> resources.
>>> As from the past renaming running resources had issues, I wanted to stop
> all 
>> resources before changing the configuration.
>>> So I was expecting the cluster to be silent until I put at least one node 
>> online again.
>>>
>>> Expectation failed. Is there a better way to do it?
>>>
>>> Regards,
>>> Ulrich
>>>
>>>
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