[ClusterLabs] Antw: [EXT] DRBD ms resource keeps getting demoted

[Ulrich Windl]

>>> Stuart Massey <djangoschef at gmail.com> schrieb am 19.01.2021 um 04:46 in
Nachricht
<CABQ68NQuTyYXcYgwcUpg5TxxaJjwhSp+c6GCOKfOwGyRQSAAjQ at mail.gmail.com>:
> So, we have a 2-node cluster with a quorum device. One of the nodes (node1)
> is having some trouble, so we have added constraints to prevent any
> resources migrating to it, but have not put it in standby, so that drbd in
> secondary on that node stays in sync. The problems it is having lead to OS
> lockups that eventually resolve themselves - but that causes it to be
> temporarily dropped from the cluster by the current master (node2).
> Sometimes when node1 rejoins, then node2 will demote the drbd ms resource.
> That causes all resources that depend on it to be stopped, leading to a
> service outage. They are then restarted on node2, since they can't run on
> node1 (due to constraints).
> We are having a hard time understanding why this happens. It seems like
> there may be some sort of DC contention happening. Does anyone have any
> idea how we might prevent this from happening?

I think if you are routing high-volume DRBD traffic throuch "the same pipe" as the cluster communication, cluster communication may fail if the pipe is satiated.
I'm not happy with that, but it seems to be that way.

Maybe running a combination of iftop and iotop could help you understand what's going on...

Regards,
Ulrich

> Selected messages (de-identified) from pacemaker.log that illustrate
> suspicion re DC confusion are below. The update_dc and
> abort_transition_graph re deletion of lrm seem to always precede the
> demotion, and a demotion seems to always follow (when not already demoted).
> 
> Jan 18 16:52:17 [21938] node02.example.com       crmd:     info:
> do_dc_takeover:        Taking over DC status for this partition
> Jan 18 16:52:17 [21938] node02.example.com       crmd:     info: update_dc:
>     Set DC to node02.example.com (3.0.14)
> Jan 18 16:52:17 [21938] node02.example.com       crmd:     info:
> abort_transition_graph:        Transition aborted by deletion of
> lrm[@id='1']: Resource state removal | cib=0.89.327
> source=abort_unless_down:357
> path=/cib/status/node_state[@id='1']/lrm[@id='1'] complete=true
> Jan 18 16:52:19 [21937] node02.example.com    pengine:     info:
> master_color:  ms_drbd_ourApp: Promoted 0 instances of a possible 1 to
> master
> Jan 18 16:52:19 [21937] node02.example.com    pengine:   notice: LogAction:
>      * Demote     drbd_ourApp:1     (            Master -> Slave
> node02.example.com )