Bootstrapping a clusteredit

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. 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 node:

  • The node name of the node.
  • The node’s hostname if is not set, because defaults 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 of the node. This is normally the IP address to which resolves 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 of the node and there are multiple nodes sharing a single IP address.

After the cluster has formed, remove the cluster.initial_master_nodes setting from each node’s configuration. It should not be set for master-ineligible nodes, master-eligible nodes joining an existing cluster, or nodes which are restarting.

If you leave cluster.initial_master_nodes in place once the cluster has formed then there is a risk that a future misconfiguration may result in bootstrapping a new cluster alongside your existing cluster. It may not be possible to recover from this situation without losing data.

The simplest way to create a new cluster is for you to select one of your master-eligible nodes that will bootstrap itself into a single-node cluster, which all the other nodes will then join. This simple approach is not resilient to failures until the other master-eligible nodes have joined the cluster. For example, if you have a master-eligible node with node name master-a then configure it as follows (omitting cluster.initial_master_nodes from the configuration of all other nodes):

cluster.initial_master_nodes: master-a

For fault-tolerant cluster bootstrapping, use all the master-eligible nodes. For instance, if your cluster has 3 master-eligible nodes with node names master-a, master-b and master-c then configure them all as follows:

  - master-a
  - master-b
  - master-c

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. If cluster.initial_master_nodes varies across the nodes on which it is set then you may bootstrap multiple clusters. It is usually not possible to recover from this situation without losing data.

Choosing a cluster nameedit

The 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.

Auto-bootstrapping in development modeedit

By default each node will automatically bootstrap itself into a single-node cluster the first time it starts. If any of the following settings are configured then auto-bootstrapping will not take place:

  • discovery.seed_providers
  • discovery.seed_hosts
  • cluster.initial_master_nodes

To add a new node into an existing cluster, configure discovery.seed_hosts or other relevant discovery settings so that the new node can discover the existing master-eligible nodes in the cluster. To bootstrap a new multi-node cluster, configure cluster.initial_master_nodes as described in the section on cluster bootstrapping as well as discovery.seed_hosts or other relevant discovery settings.