ElasticSearch Multicast not working in Linode

Question

I have 2 fresh Ubuntu Linodes in the same data centre with the same ES config except different node names. The cluster name is the same. They can each curl to each other's ElasticSearch server and there's no firewall yet in place, but multicast isn't working and I can't figure out why. They both elect themselves as master and nothing is logged about the other node or the cluster.

Is there any reason why multicast wouldn't work in an environment like this?

Answer 1

As Konstantin says in the comments, multicast is typically not supported in a multitenant environment, which makes sense, but still could have been useful for testing. Some more info here: http://blog.killtheradio.net/how-tos/keepalived-haproxy-and-failover-on-the-cloud-or-any-vps-without-multicast/

"The problem with multicast in reality is that most “cloud” (VPS) providers (AWS, Linode, Slicehost, Rackspace, etc) don’t support it on their networks. You can send a multicast message to a group, but your other machines listening on that group won’t hear it."

While there are workarounds, the simplest thing in this case is to switch to unicast.