Starting an Elasticsearch cluster for the very first time requires the initial set of master-eligible nodes to be explicitly defined on one or more of the master-eligible nodes in the cluster. This is known as cluster bootstrapping. This is only required the first time a cluster starts up: nodes that have already joined a cluster store this information in their data folder for use in a full cluster restart, and freshly-started nodes that are joining a running cluster obtain this information from the cluster’s elected master.
The initial set of master-eligible nodes is defined in the
cluster.initial_master_nodes setting. This should be
set to a list containing one of the following items for each master-eligible
- The node name of the node.
The node’s hostname if
node.nameis not set, because
node.namedefaults to the node’s hostname. You must use either the fully-qualified hostname or the bare hostname depending on your system configuration.
The IP address of the node’s transport
publish address, if it is not possible to use the
node.nameof the node. This is normally the IP address to which
network.hostresolves but this can be overridden.
The IP address and port of the node’s publish address, in the form
IP:PORT, if it is not possible to use the
node.nameof the node and there are multiple nodes sharing a single IP address.
When you start a master-eligible node, you can provide this setting on the
command line or in the
elasticsearch.yml file. After the cluster has formed,
this setting is no longer required. It should not be set for master-ineligible
nodes, master-eligible nodes joining an existing cluster, or cluster restarts.
It is technically sufficient to set
cluster.initial_master_nodes on a single
master-eligible node in the cluster, and only to mention that single node in the
setting’s value, but this provides no fault tolerance before the cluster has
fully formed. It is therefore better to bootstrap using at least three
master-eligible nodes, each with a
containing all three nodes.
You must set
cluster.initial_master_nodes to the same list of nodes
on each node on which it is set in order to be sure that only a single cluster
forms during bootstrapping and therefore to avoid the risk of data loss.
For a cluster with 3 master-eligible nodes (with node names
master-c) the configuration will look as follows:
cluster.initial_master_nodes: - master-a - master-b - master-c
Like all node settings, it is also possible to specify the initial set of master nodes on the command-line that is used to start Elasticsearch:
bin/elasticsearch -E cluster.initial_master_nodes=master-a,master-b,master-c
cluster.name setting enables you to create multiple
clusters which are separated from each other. Nodes verify that they agree on
their cluster name when they first connect to each other, and Elasticsearch
will only form a cluster from nodes that all have the same cluster name. The
default value for the cluster name is
elasticsearch, but it is recommended to
change this to reflect the logical name of the cluster.
If the cluster is running with a completely default configuration then it will automatically bootstrap a cluster based on the nodes that could be discovered to be running on the same host within a short time after startup. This means that by default it is possible to start up several nodes on a single machine and have them automatically form a cluster which is very useful for development environments and experimentation. However, since nodes may not always successfully discover each other quickly enough this automatic bootstrapping cannot be relied upon and cannot be used in production deployments.
If any of the following settings are configured then auto-bootstrapping will not
take place, and you must configure
cluster.initial_master_nodes as described
in the section on cluster bootstrapping: