[ClusterLabs] What are RHCS and LHA fence agents?

[Reid Wahl]

On Tue, Apr 8, 2025 at 12:15 AM Yan Gao <ygao at suse.com> wrote:
>
> Hi Reid,
>
> On 2025/4/8 1:52, Reid Wahl wrote:
> > On Mon, Apr 7, 2025 at 4:30 PM Reid Wahl <nwahl at redhat.com> wrote:
> >>
> >> On Mon, Apr 7, 2025 at 4:24 PM Reid Wahl <nwahl at redhat.com> wrote:
> >>>
> >>> What are RHCS and LHA fence agents, and what are they used for today?
> >>>
> >>> I would have guessed from the names and what commit messages I've found that
> >>> * RHCS refers to Red Hat Cluster Suite (a.k.a. cman clusters), which
> >>> has been unsupported since RHEL 7
> >
> > Okay, we really ought to rename this stuff soon. Pacemaker uses the
> > term "rhcs" to mean "standard fence agents" -- the kind that are from
> > the ClusterLabs/fence-agents repository. Pacemaker actually decides
> > "this agent is an RHCS-style agent" if it lives in
> > `PCMK__FENCE_BINDIR` (which is /usr/sbin on my machine) and starts
> > with "fence_".
> >
> > Sigh. Sorry to bother everyone. I'm getting frustrated by unclear and
> > legacy code :)
> >
> >>> * LHA refers to Linux-HA, which... isn't that from Heartbeat clusters
> >>> or something?
>
> Yes, they are originally from heartbeat (the major project by "Linux HA"
> community back then) and now in cluster-glue. Technically they need a
> moderator agent "fence_legacy" to be invoked.

Interesting, thanks! Do you know whether there's been any movement to
get all of these agents (or equivalent agents) into fence-agents? I
know it's not a trivial task. It just seems odd to me that after this
much time, we haven't at least deprecated the legacy stuff.

>
> >>>
> >>> All of this is from before my time as a developer for Pacemaker. I'm
> >>> trying to understand what's still relevant and how.
> >>>
> >>> I'm including Yan Gao from SUSE, as they have some commits in the past
> >>> few years related to both agent types.
> >>
> >> Related question: Is anyone aware of ANY fence agent that supports a
> >> "nodeid" parameter? We seem to have some dead code in Pacemaker
> >> related to that. I don't see any agent in fence-agents or cluster-glue
> >> (which is apparently related to LHA fencing) that accepts a nodeid
> >> parameter.
>
> Indeed so.
>
> So-called "Stonith scsi agent support" was mentioned in the PR that
> introduced this:
> https://github.com/ClusterLabs/pacemaker/pull/186

Also interesting... I didn't find that PR, because when I looked
through `git log`, I found this commit instead:
https://github.com/ClusterLabs/pacemaker/commit/c2265a12

It's not attached to any PR. These two commits appear to be identical
and both part of the main branch. Odd.

But even going back to those days (late 2012), I don't see any mention
of "nodeid" in the fence-agents repo, which included the fence_scsi
agent.

I'm inclined to get rid of the fencer code that automatically adds
this parameter.

>
> But not sure whether it had anything to do with fence_scsi agent...
>
> Regards,
>    Yan
>
>
> >
> > The nodeid question still stands.
> >
> >>
> >> --
> >> Regards,
> >>
> >> Reid Wahl (He/Him)
> >> Senior Software Engineer, Red Hat
> >> RHEL High Availability - Pacemaker
> >
> >
> >
>


-- 
Regards,

Reid Wahl (He/Him)
Senior Software Engineer, Red Hat
RHEL High Availability - Pacemaker