[ClusterLabs] how to setup single node cluster

[Reid Wahl]

On Wed, Apr 7, 2021 at 9:46 PM Strahil Nikolov <hunter86_bg at yahoo.com>
wrote:

> I always though that the setup is the same, just the node count is only
> one.
>
> I guess you need pcs, corosync + pacemaker.
> If RH is going to support it, they will require fencing. Most probably sbd
> or ipmi are the best candidates.
>

I don't think we do require fencing for single-node clusters. (Anyone at
Red Hat, feel free to comment.) I vaguely recall an internal mailing list
or IRC conversation where we discussed this months ago, but I can't find it
now. I've also checked our support policies documentation, and it's not
mentioned in the "cluster size" doc or the "fencing" doc.

The closest thing I can find is the following, from the cluster size doc[1]:
~~~
RHEL 8.2 and later: Support for 1 or more nodes

   - Single node clusters do not support DLM and GFS2 filesystems (as they
   require fencing).

~~~

To me that suggests that fencing isn't required in a single-node cluster.
Maybe sbd could work (I haven't thought it through), but conventional power
fencing (e.g., fence_ipmilan) wouldn't. That's because most conventional
power fencing agents require sending a "power on" signal after the "power
off" is complete.

[1] https://access.redhat.com/articles/3069031


> Best Regards,
> Strahil Nikolov
>
> On Thu, Apr 8, 2021 at 6:52, d tbsky
> <tbskyd at gmail.com> wrote:
> Hi:
>     I found RHEL 8.2 support single node cluster now.  but I didn't
> find further document to explain the concept. RHEL 8.2 also support
> "disaster recovery cluster". so I think maybe a single node disaster
> recovery cluster is not bad.
>
>   I think corosync is still necessary under single node cluster. or
> is there other new style of configuration?
>
>     thanks for help!
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-- 
Regards,

Reid Wahl, RHCA
Senior Software Maintenance Engineer, Red Hat
CEE - Platform Support Delivery - ClusterHA
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