I have a similar problem to you. I have more than 2 machines, but only 2 geographically redundant sites.
In your situation, you could get some redundancy by running 2 instances on one host, and 1 instance on the other host. This would protect you from temporary network glitches (because the machine with 2 instances can still form a quorum), and will protect you from failure of the machine with the single instance. It will not help you if the machine with 2 instances crashes. In this situation, where the 2 instance machine dies, you can temporarily configure the 1 instance machine to be a single instance cluster, and then when the 2 instance machine is recovered, you can reconfigure the single instance machine to be part of the 3 instance cluster again. This process is manual, and slightly dangerous, because if you restart nodes in the wrong order, you have potential to lose data. This is the approach that I have tested and seems to work, but I'd recommend testing it also. Machine A has ZK instance 1 Machine B has ZK instances 2 and 3 Machine B dies Reconfigure ZK instance 1 so that it only has itself in the cluster. This means that there is no redundancy at this point, but it can form a quorum as its the only instance in the cluster. Restart ZK instance 1 to pickup config changes Fix up Machine B Reconfigure ZK 1 instance to have ZK instances 2 and 3 in its configuration Restart ZK instance 1 to pickup config changes Start ZK instance 2 on Machine B. Wait for ZK instance 1 on Machine A and ZK instance 2 on machine B form a quorum. This is vitally important. If you start instance 3 before a quorum is formed it is possible that instances 2 and 3 will form a quorum. This will cause any updates that have occurred via instance 1 during the outage of Machine B to be lost. Start ZK instance 3 on Machine B This process should become easier once dynamic reconfiguration is implemented (in ZK 3.5 I believe?) because restarts won't be required. cheers Cam On Tue, Nov 5, 2013 at 6:05 PM, erolagnab <[email protected]> wrote: > Thanks, I got the idea now. So is it fair to say that it is not possible to > create ZK cluster providing some redundancy with 2 physical machines? If > so, > is there a way to make it happen? > > > > -- > View this message in context: > http://zookeeper-user.578899.n2.nabble.com/Running-Zookeeper-in-2-machines-tp7579232p7579237.html > Sent from the zookeeper-user mailing list archive at Nabble.com. >
