On Wed, 2020-03-11 at 02:27 +0200, Roman Hershkovich wrote: > Yes. > I have only 1 APP active at same time, and so I want this app to be > restarted whenever DB changes. Another one is a "standby" APP, where > all resources are shut. > So i thought about adding some "service" script, which will probe a > DB , and in case if it finds a CHANGE - will trigger pcs to reload a > set of resources, where one of resource would be a systemctl file, > which will continue to run a script, so in case of next change of DB > - it will restart APP set again. Is it sounds reasonable? (i don't > care of errors. I mean - i do, i want to log, but i'm ok to see them)
That sounds fine, but I'd trigger the restart by returning an error code from the db-monitoring script, rather than directly attempt to restart the resources via pcs. If you order the other resources after the db-monitoring script, pacemaker will automatically restart them when the db-monitoring script returns an error. > In addition - i thought maybe bringing PAF here could be useful - but > this is even more complex ... If bringing the db into the cluster is a possibility, that would probably be more reliable, with a quicker response too. In that case you would simply order the dependent resources after the database master promotion. pcs example: pcs constraint order promote DB-RSC then start DEPENDENT-RSC > On Tue, Mar 10, 2020 at 10:28 PM Ken Gaillot <[email protected]> > wrote: > > On Tue, 2020-03-10 at 21:03 +0200, Roman Hershkovich wrote: > > > DB servers are not in PCS cluster. Basically you say that i need > > to > > > add them to PCS cluster and then start them? but in case if DB1 > > fails > > > - DB2 autopromoted and not required start of service again> > > > > > > Regarding colocation rule - i'm kind of missing logic how it > > works - > > > how i can "colocate" 1 of 2 APP servers to be around a master DB > > ? > > > > If I understand correctly, what you want is that both apps are > > restarted if the master changes? > > > > I'm thinking you'll need a custom OCF agent for the app servers. > > The > > monitor action, in addition to checking the app's status, could > > also > > check which db is master, and return an error if it's changed since > > the > > last monitor. (The start action would have to record the initial > > master.) Pacemaker will restart the app to recover from the error. > > > > That is a little hacky because you'll have errors in the status > > every > > time the master moves, but maybe that's worth knowing in your > > situation > > anyway. > > > > > On Tue, Mar 10, 2020 at 8:42 PM Strahil Nikolov < > > > [email protected]> wrote: > > > > On March 10, 2020 7:31:27 PM GMT+02:00, Roman Hershkovich < > > > > [email protected]> wrote: > > > > >I have 2 DB servers (master/slave with replica) and 2 APP > > servers. > > > > >2 APP servers managed by pacemaker (active/passive) , but i > > want > > > > also > > > > >to > > > > >monitor "which DB is master". I can't use VIP (which could be > > > > sticked > > > > >on > > > > >master DB) - it is very limited virtual environment. > > > > > > > > > >Is it possible to create a rule or some other scenario, so in > > case > > > > if > > > > >master moved - pacemaker will restart APP (app does not > > support > > > > >failover) ? > > > > > > > > Hi Roman, > > > > > > > > If you set an order rule that starts first the master and > > then > > > > the app, during a failover the app will be stoped and once > > the > > > > master is switched (slave is promoted) the app will be > > started > > > > again. > > > > > > > > Also you can consider a colocation rule that all apps are > > > > started where the master DB is running - so the lattency > > will > > > > be minimal. > > > > > > > > Best Regards, > > > > Strahil Nikolov -- Ken Gaillot <[email protected]> _______________________________________________ Manage your subscription: https://lists.clusterlabs.org/mailman/listinfo/users ClusterLabs home: https://www.clusterlabs.org/
