Hmm. I will then work towards bringing this in. Thanks for your input. On Wed, Jun 22, 2016 at 10:44 AM, Digimer <li...@alteeve.ca> wrote:
> On 22/06/16 01:07 AM, Nikhil Utane wrote: > > 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. > > It is needed, and it is that black and white. Ask yourself, for your > particular installation; Can I run X in two places at the same time > without coordination? > > If the answer is "yes", then just do that and be done with it. > > If the answer is "no", then you need fencing to allow pacemaker to know > the state of all nodes (otherwise, the ability to coordinate is lost). > > I've never once seen a valid HA setup where fencing was not needed. I > don't claim to be the best by any means, but I've been around long > enough to say this with some confidence. > > digimer > > > Thanks everyone for the comments. > > > > -Regards > > Nikhil > > > > On Tue, Jun 21, 2016 at 10:17 PM, Digimer <li...@alteeve.ca > > <mailto: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 <mailto: > 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 > > > > > > > > > > _______________________________________________ > > 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 > > > > > -- > 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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