[ClusterLabs] Antw: [EXT] Re: Custom RA for Multi-Tenant MySQL?

[Ulrich Windl]

>>> Andrei Borzenkov <arvidjaar at gmail.com> schrieb am 11.04.2021 um 20:20 in
Nachricht <f2eb393c-52b1-af38-a684-ddd7f68d46a3 at gmail.com>:
> On 11.04.2021 20:07, Eric Robinson wrote:
>> We're writing a custom RA for a multi‑tenant MySQL cluster that runs in 
> active/standby mode. I've read the RA documentation about what exit codes 
> should be returned for various outcomes, but something is still unclear to 
> me.
>> 
>> We run multiple instances of MySQL from one filesystem, like this:
>> 
>> /app_root
>>                 /mysql1
>>                 /mysql2
>>                 /mysql3
>>                 ...etc.
>> 
>> The /app_root filesystem lives on a DRBD volume, which is only mounted on 
> the active node.
>> 
>> When the RA performs a "start," "stop," or "monitor" action on the standby

> node, the filesystem is not mounted so the mysql instances are not present.
> 
> You are not supposed to do it in the first place. You are supposed to
> have ordering constraint that starts MySQL instances after filesystem is
> available.

But probes don't care about ordering constraints.

> 
>> What should the return  codes for those actions be? Fail? Not installed? 
> Unknown error?
>> 
> 
> I believe that "not installed" is considered hard error and bans
> resource from this node. As missing filesystem is probably transient it
> does not look appropriate. There is no "fail" return code.
> 
> In any case return code depends on action. For monitor you obviously are
> expected to return "not running" in this case. "stop" should probably
> return success (after all, instance is not running, right?) And "start"
> should return error indication, but it I am not sure what is better ‑
> generic error or not running.
> 
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