[ClusterLabs] Upgrading from CentOS 6 to CentOS 7

[Ken Gaillot]

On Thu, 2019-01-03 at 19:40 +0000, Israel Brewster wrote:
> I currently have a cluster set up using pacemaker/corosync on two
> CentOS 6 boxes (fully updated). It has been requested that I
> "upgrade" the boxes to CentOS 7 (full rebuild on separate machine,
> obviously). What is it going to take to migrate the cluster with
> minimal downtime? 
> 
> The cluster is currently a mix of ipaddr2 and lsb type resources,
> with a couple of other built-in ocf types (redis, for example).
> Presumably the IPAddr and redis resources would move across no
> problem, but the lsb type resources would need to be converted to
> systemd resources. Given that (and perhaps other things?) would I be
> correct in assuming that I will not be able to simply add the new
> CentOS 7 box to the existing CentOS 6 cluster and have the config and
> everything move across automatically?

Right -- not only that, but corosync 1 (CentOS 6) and corosync 2
(CentOS 7) are not compatible for running in the same cluster.

> If I do need to build a new CentOS cluster, how can I get it fully
> set up with all the resources, but NOT let it start anything until I
> perform the cutover? Obviously it would be a bad thing for both the
> CentOS 7 box and the existing CentOS 6 boxes to have the same IP's! 

I'd make the new configuration as identical as possible to the old one,
but use some test IPs until it's ready to go live.

You can get the old config with "pcs cluster cib <filename> --config",
copy that to the new nodes, edit it as needed with "pcs -f <filename>
...", then activate it with "pcs cluster cib-push <filename> --config".

> Can I copy *any* of the config from the existing CentOS 6 boxes, or
> do I have to fully re-create all the resources from scratch on the
> CentOS 7 box? I'm assuming that initially having a "single node"
> cluster (until I can rebuild the other CentOS 6 box to CentOS 7)
> won't be an issue.

Single-node clusters are fine.

I don't know what your resources are, but you probably have some data
that will need to be copied from the old to the new when going live.
(Stop old -> sync data -> start new.)

Everything will be the same whether you want to upgrade the existing
cluster one node at a time, or replace it with a new cluster. But one
node at a time would mean you don't have high availability during the
upgrade.

For more tips, see:

http://clusterlabs.org/pacemaker/doc/en-US/Pacemaker/1.1/html-single/Pacemaker_Explained/#_upgrading

(You're stuck with the "complete cluster shutdown" method since you're
updating the OS and changing corosync major versions.)


> Thanks for any input you can provide!
> -----------------------------------------------
> Israel Brewster
> Systems Analyst II
> 5245 Airport Industrial Rd
> Fairbanks, AK 99709
> (907) 450-7293
> -----------------------------------------------