[ClusterLabs] Two-node cluster fencing

[Ken Gaillot]

On Sat, 2018-05-12 at 12:51 -0600, Casey & Gina Shobe wrote:
> Without fencing, if the primary is powered off abruptly (e.g. if one
> of your ESX servers crashes), the standby will not become primary,
> and you will need to promote it manually.  We had exactly this
> scenario happen last week with a 2-node cluster.  Without fencing,
> you don't have high availability.  If you don't need high
> availability, you probably don't need pacemaker.

To go into this a bit more, the reason it's not safe to operate without
fencing is the situation where the active node still has the IP, but
has stopped responding for whatever reason (crippling load, failed
disk, flaky network card, etc.). If the passive node brought up the IP
in this case without first fencing the active node, both VMs would
advertise the IP, and packets would (practically speaking) randomly go
to one or the other, making any sort of communication impossible.

> There are instructions for setting up fencing with vmware here:  http
> s://www.hastexo.com/resources/hints-and-kinks/fencing-vmware-
> virtualized-pacemaker-nodes/
> 
> One note - rather than the SDK, I believe you actually need the CLI
> package, which can be found here:  https://my.vmware.com/web/vmware/d
> etails?downloadGroup=VCLI600&productId=491
> 
> Good luck - I haven't managed to get it to build yet - vmware gives
> you a black box installer script that compiles a bunch of dependent
> perl modules, and it ends up getting hung with 100% CPU usage for
> days - digging into this further with lsof and friends, it seems to
> be prompting for where your apache source code is to compile
> mod_perl.  Why does it need mod_perl for the CLI??  Anyways, I
> haven't managed to get past that roadblock yet.  I'm using Ubuntu 16
> so it may happen to just work better on your RHEL instances.  If you
> have a different ESX version than 6.0, you may have better luck as
> well.
> 
> Best wishes,
-- 
Ken Gaillot <kgaillot at redhat.com>