ES7: Do we need cluster.initial_master_nodes when a node restarts?

[UDixit]

As per the documents, we need Cluster.initial_master_nodes only for the first bootstrap of the cluster.

1. How does a node join the cluster when it restarts? Does it only need the sed_hosts to discover others?
2. What if the entire cluster went down? will the nodes use the initial_master_node setting?
3. Since in most cases, we gradually add nodes to the cluster the initial_master_nodes setting should always be the very first node that started. In what scenarios will you add 2 or more nodes names to this setting?

[DavidTurner]

@UDixit

How does a node join the cluster when it restarts? Does it only need the seed_hosts to discover others?

Yes, that's right.

@UDixit

What if the entire cluster went down? will the nodes use the initial_master_node setting?

No, it's only used the very first time the cluster starts.

@UDixit

In what scenarios will you add 2 or more nodes names to this setting?

It's ok to start your nodes one-at-a-time if you want, but it's not unusual to start up all the nodes at once to make sure that it's fault-tolerant right from the start.

[UDixit]

Thanks for the prompt reply. Really appreciated.

So there is no harm in populating the cluster.initial_master_nodes repeatedly.
It should simply get ignored

[DavidTurner]

@UDixit

So there is no harm in populating the cluster.initial_master_nodes repeatedly.
It should simply get ignored

It's safest to remove it as soon as possible after the cluster has started up for the first time, which is what the docs recommend:

You should not use this setting when restarting a cluster or adding a new node to an existing cluster.

It's mostly ok to leave it in place, but that does open the door to some (really rare) failure scenarios that can result in data loss.