[ClusterLabs] Custom RA for Multi-Tenant MySQL?
eric.robinson at psmnv.com
Sun Apr 11 14:47:59 EDT 2021
> -----Original Message-----
> From: Users <users-bounces at clusterlabs.org> On Behalf Of Andrei
> Sent: Sunday, April 11, 2021 1:20 PM
> To: users at clusterlabs.org
> Subject: Re: [ClusterLabs] Custom RA for Multi-Tenant MySQL?
> 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
> > 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.
That is what we have. The colocation constraints require mysql -> filesystem -> drbd master. The ordering constraints promote drbd, then start the filesystem, then start mysql.
> > 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.
That's a big part of my question. I'm just trying to avoid a condition where the mysql resource is running on node A, and Pacemaker thinks there is a "problem" with it on Node B.
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