On Thu, 2021-07-22 at 10:48 -0400, john tillman wrote: > There was a lot of discussion on this topic which might have > overshadowed > this question so I will ask it again in case someone missed it. > > It comes from a post (see below) that we were pointed to here by > Andrei: > > Is there something like the described "ping tiebreaker" in the > current > world of pacemaker/corosync? > > Best Regards, > -John
corosync-qdevice is the closest ... you run qdevice on the third node and the cluster nodes talk to it there's also fence_heuristics_ping to allow a node to fence another node only if it can ping an address (to ensure that a node with connectivity survives a split-brain). this requires some fencing device to be configured. > > Interesting read. Thank you for providing it! > > > > In this follow up post > > https://techthoughts.typepad.com/managing_computers/2007/10/more-about-quor.html > > the author mentions the following: > > > > Ping tiebreaker > > > > Some HA systems provide a ping tiebreaker. To make this work, you > > pick a > > address outside the cluster to ping, and any partition that can > > ping that > > address has quorum. The obvious advantage is that it's very simple > > to set > > up - doesn't require any additional servers or shared disk. The > > disadvantage (and it's a big one) is that it's very possible for > > multiple > > partitions to think they have quorum. In the case of split-site > > (disaster > > recovery) type clusters, it's going to happen fairly often. If you > > can > > use this method for a single site in conjunction with fencing, then > > it > > will likely work out quite well. It's a lot better than no > > tiebreaker, or > > one that always says "you have quorum". Having said that, it's > > significantly inferior to any of the other methods. > > > > The quote "It's a lot better than no tiebreaker..." is what I am > > looking > > for. Is there something like a "ping tiebreaker" in the current > > world of > > pacemaker/corosync? > > > > Thanks to all those who have already commented on my question. I > > appreciate the input/education. > > > > Best Regards, > > -John > > > > > > > > > On Wed, Jul 21, 2021 at 3:55 PM Ulrich Windl > > > <ulrich.wi...@rz.uni-regensburg.de> wrote: > > > > > > > > Hi! > > > > > > > > Maybe someone feels motivated to write some article comparing > > > > the > > > > concepts > > > > * split brain > > > > * quorum > > > > * fencing > > > > > > > > > > Yet another one? Using your own reply "search is free". > > > > > > https://techthoughts.typepad.com/managing_computers/2007/10/split-brain-quo.html > > > > > > > There are eight possible states that I tried to illustrate on > > > > the > > > > attached sketch (S="Split Brain", "Q=Quorum, F=Fencing). > > > > > > > > ;-) > > > > > > > > Regards, > > > > Ulrich > > > > > > > > > > > > > > > Andrei Borzenkov 21.07.2021, 07:52 >>> > > > > > > > > On 21.07.2021 07:28, Strahil Nikolov via Users wrote: > > > > > Hi, > > > > > consider using a 3rd system as a Q disk. > > > > > > > > What was not clear in "Quorum is a different concept and > > > > doesn't remove > > > > the need for fencing"? > > > > > > > > > Also, you can use iscsi from that node as a SBD device, so > > > > > you will > > > > > > > > have proper fencing .If you don't have a hardware watchdog > > > > device, you > > > > can use softdog kernel module for that. > > > > > Best Regards,Strahil Nikolov > > > > > > > > > > > > > > > On Wed, Jul 21, 2021 at 1:45, Digimer<li...@alteeve.ca> > > > > > wrote: On > > > > > > > > 2021-07-20 6:04 p.m., john tillman wrote: > > > > > > Greetings, > > > > > > > > > > > > Is it possible to configure a two node cluster (pacemaker > > > > > > 2.0) > > > > > > > > without > > > > > > fencing and avoid split brain? > > > > > > > > > > No. > > > > > > > > > > > I was hoping there was a way to use a 3rd node's ip > > > > > > address, like > > > > > > > > from a > > > > > > network switch, as a tie breaker to provide quorum. A > > > > > > simple > > > > > > > > successful > > > > > > ping would do it. > > > > > > > > > > Quorum is a different concept and doesn't remove the need for > > > > > > > > fencing. > > > > > > > > > > > I realize that this 'ping' approach is not the bullet proof > > > > > > solution > > > > > > > > that > > > > > > fencing would provide. However, it may be an improvement > > > > > > over two > > > > > > > > nodes > > > > > > alone. > > > > > > > > > > It would be, at best, a false sense of security. > > > > > > > > > > > Is there a configuration like that already? Any other > > > > > > ideas? > > > > > > > > > > > > Pointers to useful documents/discussions on avoiding split > > > > > > brain > > > > > > > > with > > > > two > > > > > > node clusters would be welcome. > > > > > > > > > > https://www.alteeve.com/w/The_2-Node_Myth > > > > > > > > > > (note: currently throwing a cert error related to the let's > > > > > encrypt > > > > > issue, should be cleared up soon). > > > > > > > > > > > > > > > _______________________________________________ > > > > > Manage your subscription: > > > > > https://lists.clusterlabs.org/mailman/listinfo/users > > > > > > > > > > ClusterLabs home: https://www.clusterlabs.org/ > > > > > > > > > > > > > _______________________________________________ > > > > Manage your subscription: > > > > https://lists.clusterlabs.org/mailman/listinfo/users > > > > > > > > ClusterLabs home: https://www.clusterlabs.org/ > > > > > > > > _______________________________________________ > > > > Manage your subscription: > > > > https://lists.clusterlabs.org/mailman/listinfo/users > > > > > > > > ClusterLabs home: https://www.clusterlabs.org/ > > > > > > _______________________________________________ > > > Manage your subscription: > > > https://lists.clusterlabs.org/mailman/listinfo/users > > > > > > ClusterLabs home: https://www.clusterlabs.org/ > > > > > > > > > > > > _______________________________________________ > > Manage your subscription: > > https://lists.clusterlabs.org/mailman/listinfo/users > > > > ClusterLabs home: https://www.clusterlabs.org/ > > > > > > > _______________________________________________ > Manage your subscription: > https://lists.clusterlabs.org/mailman/listinfo/users > > ClusterLabs home: https://www.clusterlabs.org/ > -- Ken Gaillot <kgail...@redhat.com> _______________________________________________ Manage your subscription: https://lists.clusterlabs.org/mailman/listinfo/users ClusterLabs home: https://www.clusterlabs.org/
