On 01/20/2013 08:09 PM, Alex Sudakar wrote: > I'm setting up a very basic two-node active/passive cluster using > Pacemaker 1.1.7 and Corosync 1.4.1 under Red Hat Enterprise Linux 6.3. > The cluster is running a web application that needs to be accessed by > our separate LAN of desktops. > > With only two nodes comprising the cluster I believe a quorum is > impossible, so I've set no-quorum-policy to 'ignore'. However I was > wondering if there is a possibility of using one or more 'tie breaker' > devices/resources to determine a proper quorum? I _think_ I've seen > mention of such a thing in passing in this list; I'm not sure. > > I was thinking I could designate a 'tie breaker' device in the desktop > LAN; any node that could access that device - ping it, say - would > gain an extra quorum vote, something like that. But then I realized > that this could be achieved by simply setting up that LAN device as a > proper member of the cluster, with location constraints set to ensure > that no resource could ever run on it. Then the normal cluster > membership mechanics and quorum calculations would take the third node > into account in determining its quorums. If one of the two 'real' > nodes couldn't connect to the desktop LAN node then it wouldn't be > part of the quorum. > > What is the proper way to set up a 'tie breaker' situation for a > simple two-node Pacemaker cluster? Is there a 'tie breaker' facility > - ping a device and get a vote? - or does one just set up a bare-bones > third node purely for membership/quorum purposes? > > I have another question I'd like to ask to properly try and understand > how cluster membership works. If I have three nodes, A, B & C, all > using unicast UDP, with A & B able to connect to C but not to each > other - i.e. A-C works, B-C works, but not A-B - will the three nodes > all be seen as connected in a single quorum/group? If not, what > happens? In wondering about this I realized that I didn't know if > Corosync requires _direct_ communication between all cluster nodes or > if nodes can 'relay' transmissions between machines that can't contact > each other directly. Will C 'relay' connectivity/membership between A > & B? > > Thank you for any help!
The "device" you are thinking of is probably "quorum disk", or "qdisk". In the early days of red hat clustering, this was required. Then it became optional and now it's falling out of favour. It's still usable though and you can use it with pacemaker by adding cman. What you really need though is stonith, also known as fencing. In a two node cluster, if there is a break between the nodes, they'll reach out over another network channel and the faster one will power off the slower one. This is needed anyway, for safety reasons (prevents "split-brains") and it's an effective tie-breaker. -- Digimer Papers and Projects: https://alteeve.ca/w/ What if the cure for cancer is trapped in the mind of a person without access to education? _______________________________________________ Linux-HA mailing list [email protected] http://lists.linux-ha.org/mailman/listinfo/linux-ha See also: http://linux-ha.org/ReportingProblems
