Thank you for this! One last thing I need to clear out before digging into your configuration specs etc. Since the pacemaker is a fail-over system rather than a load-balancing system (like Red Hat) as you say, my understanding is that one of my nodes will have the VIP until: 1) Tomcat crashes and can not restart (dead for some reason) --> Pacemaker migrates VIP
2) The network communication with the outside network is cut off. --> Pacemaker migrates VIP If these (2) are valid (are they?) then that means that there is no primary/backup concept using pacemaker (since I will assign to one of my nodes to have the VIP and my installed Load Balancer will distribute the load among my 2 Tomcats) and as a result there can not be a split-brain. Yet you imply that split-brain can occur even with Pacemaker if I don't have fencing properly set. But how? Since it seems to me that Pacemaker does not have a notion of primary/backup. Or you mean something else with "fail-over" system? Additionally you say that the "coordination" of Pacemaker instances is done via corosync which is over network messages right? So what happens in the event of communication/network failure but only in the communication paths used for corosync coordination and not the communication path with the clients? Hope this question makes sense as I am new in your facilities. Thank you for your help! ________________________________ From: Digimer <[email protected]> To: Hermes Flying <[email protected]>; General Linux-HA mailing list <[email protected]> Sent: Saturday, December 1, 2012 2:35 AM Subject: Re: [Linux-HA] Some help on understanding how HA issues are addressed by pacemaker On 11/30/2012 05:04 PM, Hermes Flying wrote: > Hi, > I am looking into using your facilities to have high availability on my > system. I am trying to figure out some things. I hope you guys could help me. > I am interested in knowing how pacemaker migrates a VIP and how a splitbrain > situation is address by your facilities. > To be specific: I am interested in the following setup: > > 2 linux machines. Each machine runs a load balancer and a Tomcat instance. > If I understand correctly pacemaker will be responsible to assign the main > VIP to one of the nodes. Pacemaker can handle virtual IP addresses, but it's more of a fail-over system, rather than a load-balancing, round-robin system. For load balancing, look at Red Hat's "LVS". > My questions are: > 1)Will pacemaker monitor/restart the load balancers on each machine in case > of crash? It can monitor/recover/relocate any service that uses init.d style scripts. If a script/service responds properly to stop, status and start, you're good to go. > 2) How does pacemaker decide to migrate the VIP to the other node? At the most simple; When the machine hosting the VIP fails, it will relocate. You can control how, when and where the VIP fails back (look at 'resource stickiness'). > 3) Do the pacemakers in each machine communicate? If yes how do you handle > network failure? Could I end up with split-brain? Pacemaker uses corosync for cluster membership, quorum and fencing. A properly configured fence device (aka "stonith"), will prevent a split brain. If you disable or fail to properly setup fencing, split brains are possible and even likely. > 4) Generally how is split-brain addressed using pacemaker? Fencing to prevent it. > 5) Could pacemaker monitor Tomcat? If it supports stop, start and status, yes. > As you can see I am interested in maintain quorum in a two-node > configuration. If you can help me with this info to find a proper direction > it would be much appreciated! Quorum needs to be disabled in a two-node cluster. This is fine with good fencing. To learn more, please see the documentation available here: http://clusterlabs.org/doc/ -- 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
