> 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. >
Thank you. I'll check into "corosync-qdevice". I had already stumbled across the "heuristics ping" and noted the fence device requirement. Thank you for confirming that. >> > 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 >> > > <[email protected]> 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<[email protected]> >> > > > > 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 <[email protected]> > > _______________________________________________ > 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/
