[ClusterLabs] Preferred node for a service (not constrained)

[Dan Swartzendruber]

On 2020-11-30 23:21, Petr Bena wrote:
> Hello,
> 
> Is there a way to setup a preferred node for a service? I know how to
> create constrain that will make it possible to run a service ONLY on
> certain node, or constrain that will make it impossible to run 2
> services on same node, but I don't want any of that, as in
> catastrophical scenarios when services would have to be located 
> together
> on same node, this would instead disable it.
> 
> Essentially what I want is for service to be always started on 
> preferred
> node when it is possible, but if it's not possible (eg. node is down) 
> it
> would freely run on any other node, with no restrictions and when node
> is back up, it would migrate back.
> 
> How can I do that?

I do precisely this for an active/passive NFS/ZFS storage appliance 
pair.
One of the VSA has more memory and is less used, so I have it set to 
prefer
that host.

https://clusterlabs.org/pacemaker/doc/en-US/Pacemaker/1.1/html/Clusters_from_Scratch/_prefer_one_node_over_another.html

I believe I used the value infinity, so it will prefer the 2nd host over 
the 1st if at all possible.  My 'pcs constraint':

[root at centos-vsa2 ~]# pcs constraint
Location Constraints:
   Resource: group-zfs
     Enabled on: centos-vsa2 (score:INFINITY)
Ordering Constraints:
Colocation Constraints:
Ticket Constraints: