Network changes

Elasticsearch 2.x will only bind to localhost by default. It will try to bind to both 127.0.0.1 (IPv4) and [::1] (IPv6), but will work happily in environments where only IPv4 or IPv6 is available. This change prevents Elasticsearch from trying to connect to other nodes on your network unless you specifically tell it to do so. When moving to production you should configure the network.host parameter, either in the elasticsearch.yml config file or on the command line:

bin/elasticsearch --network.host 192.168.1.5
bin/elasticsearch --network.host _non_loopback_

The full list of options that network.host accepts can be found in the Network Settings.

Multicast has been removed (although it is still provided as a plugin for now). Instead, and only when bound to localhost, Elasticsearch will use unicast to contact the first 5 ports in the transport.tcp.port range, which defaults to 9300-9400.

This preserves the zero-config auto-clustering experience for the developer, but it means that you will have to provide a list of unicast hosts when moving to production, for instance:

discovery.zen.ping.unicast.hosts: [ 192.168.1.2,  192.168.1.3 ]

You don’t need to list all of the nodes in your cluster as unicast hosts, but you should specify at least a quorum (majority) of master-eligible nodes. A big cluster will typically have three dedicated master nodes, in which case we recommend listing all three of them as unicast hosts.