# Clustering questions **URL:** \ **Category:** Elasticsearch\ **Created:** [March 20, 2013, 5:31am UTC](https://discuss.elastic.co/t/clustering-questions/11216 "2013-03-20T05:31:33Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Matt\_Chambers](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/matt_chambers/32/607_2.png) [@Matt\_Chambers](https://discuss.elastic.co/u/Matt_Chambers)\ **Post date:** [March 20, 2013, 5:31am UTC](https://discuss.elastic.co/t/clustering-questions/11216/1 "2013-03-20T05:31:33Z")
Hey everyone, have some questions about clustering. Most of my problems have been solved just reading this group, but I'm getting close to going into production and had a couple questions. Currently if I restart the master, the cluster breaks up, or at least the nodes all declare themselves new masters. For whatever reason multicast is disabled on our network. Does this mean that each host must have a list of all other hosts in the cluster, like this: discovery.zen.ping.multicast.enabled: false discovery.zen.ping.unicast.hosts: ["192.168.49.252:9301", host2, host3, host4] -Matt -- You received this message because you are subscribed to the Google Groups "elasticsearch" group. To unsubscribe from this group and stop receiving emails from it, send an email to [elasticsearch+unsubscribe@googlegroups.com](mailto:elasticsearch+unsubscribe@googlegroups.com). For more options, visit [https://groups.google.com/groups/opt\_out](https://groups.google.com/groups/opt_out). ---
**Author:** ![dadoonet](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/dadoonet/32/137187_2.png) [@dadoonet](https://discuss.elastic.co/u/dadoonet)\ **Post date:** [March 20, 2013, 6:28am UTC](https://discuss.elastic.co/t/clustering-questions/11216/2 "2013-03-20T06:28:34Z")
Must have: no. Should have: yes. You need at least one other node but I recommend to add all existing nodes if you have only 4 nodes. Also, to avoid split brain issues consider setting discovery.zen.minimum\_master\_nodes to 2 or 3. ## HTH David 😉 Twitter : @dadoonet / @elasticsearchfr / @scrutmydocs Le 20 mars 2013 à 06:31, Matt Chambers [yougotrooted@gmail.com](mailto:yougotrooted@gmail.com) a écrit : Hey everyone, have some questions about clustering. Most of my problems have been solved just reading this group, but I'm getting close to going into production and had a couple questions. Currently if I restart the master, the cluster breaks up, or at least the nodes all declare themselves new masters. For whatever reason multicast is disabled on our network. Does this mean that each host must have a list of all other hosts in the cluster, like this: discovery.zen.ping.multicast.enabled: false discovery.zen.ping.unicast.hosts: ["192.168.49.252:9301", host2, host3, host4] ## -Matt You received this message because you are subscribed to the Google Groups "elasticsearch" group. To unsubscribe from this group and stop receiving emails from it, send an email to [elasticsearch+unsubscribe@googlegroups.com](mailto:elasticsearch+unsubscribe@googlegroups.com). For more options, visit [https://groups.google.com/groups/opt\_out](https://groups.google.com/groups/opt_out). -- You received this message because you are subscribed to the Google Groups "elasticsearch" group. To unsubscribe from this group and stop receiving emails from it, send an email to [elasticsearch+unsubscribe@googlegroups.com](mailto:elasticsearch+unsubscribe@googlegroups.com). For more options, visit [https://groups.google.com/groups/opt\_out](https://groups.google.com/groups/opt_out). ---
**Author:** ![Clinton\_Gormley](https://avatars.discourse-cdn.com/v4/letter/c/50afbb/32.png) [@Clinton\_Gormley](https://discuss.elastic.co/u/Clinton_Gormley)\ **Post date:** [March 20, 2013, 12:23pm UTC](https://discuss.elastic.co/t/clustering-questions/11216/3 "2013-03-20T12:23:32Z")
Hiya > Currently if I restart the master, the cluster breaks up, or at least > the nodes all declare themselves new masters. > For whatever reason multicast is disabled on our network. Does this > mean that each host must have a list of all other hosts in the > cluster, like this: > > discovery.zen.ping.multicast.enabled: false > discovery.zen.ping.unicast.hosts: ["192.168.49.252:9301", host2, > host3, host4] Multicast/unicast discovery is used only when starting a new cluster, not when a cluster is already running. The setting that you want is minimum\_master\_nodes. This specifies the minimum number of master-eligible nodes (ie nodes that are allowed to become master) that a node must be able to see in order for it to form a cluster. If a node sees to few other nodes, then it doesn't form a cluster, but keeps looking for more nodes or an existing cluster. minimum\_master\_nodes should be set to: int(num\_nodes/2)+1 (ie the majority) What you describe above seems very weird to me. If you have managed to form a cluster of eg 4 nodes, then shutdown the master, the other three nodes should elect a new master and continue as a cluster. They shouldn't disconnect from each other (unless of course they are unable to communicate). Try replicating this situation, and check the cluster health on all nodes while you're doing it (and the logs on all nodes) to figure out exactly what is happening. clint -- You received this message because you are subscribed to the Google Groups "elasticsearch" group. To unsubscribe from this group and stop receiving emails from it, send an email to [elasticsearch+unsubscribe@googlegroups.com](mailto:elasticsearch+unsubscribe@googlegroups.com). For more options, visit [https://groups.google.com/groups/opt\_out](https://groups.google.com/groups/opt_out). ---
**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\ **Post date:** [July 6, 2017, 2:45am UTC](https://discuss.elastic.co/t/clustering-questions/11216/4 "2017-07-06T02:45:37Z")