I don't get it. Pacemaker + Corosync is providing me so much of functionality. For e.g. if we leave out the condition of split-brain for a while, then it provides: 1) Discovery and cluster formation 2) Synchronization of data 3) Heartbeat mechanism 4) Swift failover of the resource 5) Guarantee that one resource will be started on only 1 node
So in case of normal fail-over we need the basic functionality of resource being migrated to a standby node. And it is giving me all that. So I don't agree that it needs to be as black and white as you say. Our solution has different requirements than a typical HA solution. But that is only now. In the future we might have to implement all the things. So in that sense Pacemaker gives us a good framework that we can extend. BTW, we are not even using a virtual IP resource which again I believe is something that everyone employs. Because of the nature of the service a small glitch is going to happen. Using virtual IPs is not giving any real benefit for us. And with regard to the question, why even have a standby and let it be active all the time, two-node cluster is one of the possible configuration, but main requirement is to support N + 1. So standby node doesn't know which active it has to take over until a failover occurs. Your comments however has made me re-consider using fencing. It was not that we didn't want to do it. Just that I felt it may not be needed. So I'll definitely explore this further. Thanks everyone for the comments. -Regards Nikhil On Tue, Jun 21, 2016 at 10:17 PM, Digimer <li...@alteeve.ca> wrote: > On 21/06/16 10:57 AM, Dmitri Maziuk wrote: > > On 2016-06-20 17:19, Digimer wrote: > > > >> Nikhil indicated that they could switch where traffic went up-stream > >> without issue, if I understood properly. > > > > They have some interesting setup, but that notwithstanding: if split > > brain happens some clients will connect to "old master" and some: to > > "new master", dep. on arp update. If there's a shared resource > > unavailable on one node, clients going there will error out. The other > > ones will not. It will work for some clients. > > > > Cf. both nodes going into stonith deathmatch and killing each other: the > > service now is not available for all clients. What I don't get is the > > blanket assertion that this "more highly" available that option #1. > > > > Dimitri > > As I've explained many times (here and on IRC); > > If you don't need to coordinate services/access, you don't need HA. > > If you do need to coordinate services/access, you need fencing. > > So if Nikhil really believes s/he doesn't need fencing and that > split-brains are OK, then drop HA. If that is not the case, then s/he > needs to implement fencing in pacemaker. It's pretty much that simple. > > -- > 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? > > _______________________________________________ > Users mailing list: Users@clusterlabs.org > http://clusterlabs.org/mailman/listinfo/users > > Project Home: http://www.clusterlabs.org > Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf > Bugs: http://bugs.clusterlabs.org >
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