Did a cluster shutdown (all nodes) and then upgraded node by node from 2.4.6 to 5.3.2 and started cluster again node by node, but they all just continually complains like this:
[2017-10-26T23:21:48,072][WARN ][o.e.d.z.ZenDiscovery ] [d1r2n9] not enough master nodes discovered during pinging (found [[Candidate{node={d1r2n9}{jJ3HFWbhSfudgfaK4w-y8A}{yCVvctQ3TR6ye1k9txj6cg}{<ip>}{<ip>:9300}{rack=OPA3.4.16}, clusterStateVersion=-1}]], but needed [8]), pinging again
even though I've restart all 14 nodes again.
In 2.4.6 we used:
discovery.zen.ping.multicast.enabled: false
discovery.zen.ping.unicast.hosts: [<list of nodes>]
but had to remove this to start 5.3.2 nodes, believe I've read somewhere than 5.x now only uses unicast for cluster communication anyway.
Hints appreciated to rejoin cluster, TIA!
Solved: still had to defined the ping unicast host list