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

[Strahil Nikolov]

Constraints' values are varying from:
infinity which equals to score of 1000000
to:
- infinity which equals to score of -1000000

You can usually set a positive score on the prefered node which is bigger than on the other node.

For example setting a location constraint like this will prefer node1:
node1 - score 10000
node2 - score 5000

In order to prevent unnecessary downtime , you should also consider setting stickiness.

For example a stickiness of 20000 will overwhelm the score of 10000 on the recently recovered node1 and will prevent the resource of being stopped and relocated from node2 to node1 .

Note: default stickiness is per resource , while the total stickiness score of a group is calculated based on the scores of all resources in it.

Best Regards,
Strahil Nikolov





В сряда, 2 декември 2020 г., 16:54:43 Гринуич+2, Dan Swartzendruber <dswartz at druber.com> написа: 





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:

_______________________________________________
Manage your subscription:
https://lists.clusterlabs.org/mailman/listinfo/users

ClusterLabs home: https://www.clusterlabs.org/