[ClusterLabs] how to setup single node cluster

[Klaus Wenninger]

On 4/8/21 8:16 AM, Reid Wahl wrote:
>
>
> On Wed, Apr 7, 2021 at 9:46 PM Strahil Nikolov <hunter86_bg at yahoo.com 
> <mailto: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.
And moreover you have to be alive enough to kick off
conventional power fencing to self-fence ;-)
With sbd the hardware-watchdog should kick in.

Klaus
>
> [1] https://access.redhat.com/articles/3069031 
> <https://access.redhat.com/articles/3069031>
>
>
>     Best Regards,
>     Strahil Nikolov
>
>         On Thu, Apr 8, 2021 at 6:52, d tbsky
>         <tbskyd at gmail.com <mailto: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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