[ClusterLabs] multi-state constraints

[Andrei Borzenkov]

On 10.05.2021 20:36, Alastair Basden wrote:
> Hi Andrei,
> 
> Thanks.  So, in summary, I need to:
> pcs resource create resourcedrbd0 ocf:linbit:drbd drbd_resource=disk0 op
> monitor interval=60s
> pcs resource master resourcedrbd0Clone resourcedrbd0 master-max=1
> master-node-max=1 clone-max=2 clone-node-max=1 notify=true
> 
> pcs constraint location resourcedrb0Clone prefers node1=100
> pcs constraint location resourcedrb0Clone prefers node2=50
> pcs constraint location resourcedrb0Clone avoids node3
> pcs constraint location resourcedrb0Clone avoids node4
> 
> Does this mean that it will prefer to run as master on node1, and slave
> on node2?

No. I already told you so.

>  If not, how can I achieve that?
>

DRBD resource agents sets master scores based on disk state. If you
statically override this decision you are risking promoting stale copy
which means data loss (I do not know if agent allows it, hopefully not;
but then it will continue to attempt to promote wrong copy and
eventually fail). But if you insist, it is documented:

https://clusterlabs.org/pacemaker/doc/en-US/Pacemaker/2.0/html/Pacemaker_Explained/s-promotion-scores.html

Also statically biasing one single node means workload will be relocated
every time node becomes available, which usually implies additional
downtime. That is something normally avoided (which is why resource
stickiness exists).