Elasticsearch: Configurations when adding new nodes to a running cluster (Discovery)

[ege]

I have an Elastic cluster with 2 dedicated Master nodes and 2 dedicated Data nodes. I'm currently trying to add 4 new nodes to this running cluster.

In the documentation, I have seen there should be at least 3 Master nodes, for a large resilient cluster, so, I thought one of the new nodes to be a Master, Voting_Only and Data node; the Voting_Only role is given as per this. The other 3 will be dedicated Data nodes.

In the configuration files of all of the 4 new nodes, I have added the discovery.seed_hosts setting with the IPs of the 2 Master nodes of the previous cluster, as per my understanding I got from this and this. But, I have doubts with that setting,

• Should the discovery.seed_hosts setting contain the IPs of all the available Master nodes in the cluster and if so, does it mean I should be editing the config files of the previous nodes and restarting the cluster?

OR

• Is it fine to just have the IPs of the 2 Master nodes of the previous cluster in the new nodes?

The cluster.initial_master_nodes setting is set in the previous nodes and I'm not setting it in the new nodes as per this.

• Is it okay to have that setting not removed from the previous nodes unless there is a cluster restart?

Your kind help would be appreciated.

[DavidTurner]

@ege

Should the discovery.seed_hosts setting contain the IPs of all the available Master nodes in the cluster and if so, does it mean I should be editing the config files of the previous nodes and restarting the cluster?

Yes and yes.

@ege

• Is it okay to have that setting not removed from the previous nodes unless there is a cluster restart ?

Not really, a node might restart at any time. You should fix the config now just in case.

In practice the cluster will appear to work fine without restarting the running nodes to pick up these config changes, but you should still fix the config and then do a rolling restart to validate that you adjusted each node's config correctly. If you don't do the restart yourself then you risk leaving a typo in your config that won't be noticed until a node restarts for a reason outside of your control.

[ege]

Hi @DavidTurner! Thank you so much for the response!

That's great to know and I will change the configuration as you said.