[Pacemaker] unknown third node added to a 2 node cluster?

[Brian J. Murrell (brian)]

On Wed, 2014-10-08 at 12:39 +1100, Andrew Beekhof wrote:
> On 8 Oct 2014, at 2:09 am, Brian J. Murrell (brian) <brian-SquOHqY54CVWr29BmMi2cA at public.gmane.org> wrote:
> 
> > Given a 2 node pacemaker-1.1.10-14.el6_5.3 cluster with nodes "node5"
> > and "node6" I saw an "unknown" third node being added to the cluster,
> > but only on node5:
> 
> Is either node using dhcp?

Yes, they both are.  The server is the ISC DHCP server (on EL6) and the
address pool is much more plentiful than the node count.  That is all
just to say that the DHCP server serving these nodes abides by the DHCP
RFC's recommendation to allow clients to continue to use addresses they
have already been assigned when making a renewal request.  And indeed,
give them the same address they had previously after a lease expiry, as
long as the pool is not constrained and address needed to satisfy a
request from a different machine.

> I would guess node6 got a new IP address

These nodes are using the ISC DHCP client.  That DHCP client logs in the
same log (/var/log/messages) as was posted in my prior message when it
renews a lease with messages such as:

Oct 10 05:56:19 node6 dhclient[1026]: DHCPREQUEST on eth0 to 10.14.80.6 port 67 (xid=0x4f11c576)
Oct 10 05:56:19 node6 dhclient[1026]: DHCPACK from 10.14.80.6 (xid=0x4f11c576)
Oct 10 05:56:20 node6 dhclient[1026]: bound to 10.14.82.141 -- renewal in 8546 seconds.

In the logs that I pasted the messages from in my previous message, such
messages don't even exist because the nodes are not left up long enough
to even get to a lease expiry.  These are tests nodes and so are
rebooted frequently.

TL;DR: I am quite certain the node did not get a new/different address.

> (or that corosync decided to bind to a different one)

Bind to a different what?  Address?  As in binding to an address that
was not even configured on the machine?

b.