Constraints' values are varying from:
infinity which equals to score of 100
to:
- infinity which equals to score of -100
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 1
node2 - score 5000
In order to prevent unnecessary downtime , you should also consider setting
stickiness.
For example a stickiness of 2 will overwhelm the score of 1 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
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@centos-vsa2 ~]# pcs constraint
Location Constraints:
Resource: group-zfs
Enabled on: centos-vsa2 (score:INFINITY)
Ordering Constraints:
Colocation Constraints:
Ticket Constraints:
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