152 lines
7.6 KiB
Plaintext
152 lines
7.6 KiB
Plaintext
[[modules-discovery-bootstrap-cluster]]
|
|
=== Bootstrapping a cluster
|
|
|
|
Starting an Elasticsearch cluster for the very first time requires the initial
|
|
set of <<master-node,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 <<restart-upgrade,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
|
|
<<initial_master_nodes,`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,node name>> of the node.
|
|
- The node's hostname if `node.name` is not set, because `node.name` defaults
|
|
to the node's hostname. You must use either the fully-qualified hostname or
|
|
the bare hostname <<modules-discovery-bootstrap-cluster-fqdns,depending on
|
|
your system configuration>>.
|
|
- The IP address of the node's <<modules-transport,publish address>>, if it is
|
|
not possible to use the `node.name` of the node. This is normally the IP
|
|
address to which <<common-network-settings,`network.host`>> resolves but
|
|
<<advanced-network-settings,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.name` of 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 `cluster.initial_master_nodes` setting
|
|
containing all three nodes.
|
|
|
|
WARNING: 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.name,node names>>
|
|
`master-a`, `master-b` and `master-c`) the configuration will look as follows:
|
|
|
|
[source,yaml]
|
|
--------------------------------------------------
|
|
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:
|
|
|
|
[source,bash]
|
|
--------------------------------------------------
|
|
$ bin/elasticsearch -Ecluster.initial_master_nodes=master-a,master-b,master-c
|
|
--------------------------------------------------
|
|
|
|
[NOTE]
|
|
==================================================
|
|
|
|
[[modules-discovery-bootstrap-cluster-fqdns]] The node names used in the
|
|
`cluster.initial_master_nodes` list must exactly match the `node.name`
|
|
properties of the nodes. By default the node name is set to the machine's
|
|
hostname which may or may not be fully-qualified depending on your system
|
|
configuration. If each node name is a fully-qualified domain name such as
|
|
`master-a.example.com` then you must use fully-qualified domain names in the
|
|
`cluster.initial_master_nodes` list too; conversely if your node names are bare
|
|
hostnames (without the `.example.com` suffix) then you must use bare hostnames
|
|
in the `cluster.initial_master_nodes` list. If you use a mix of fully-qualifed
|
|
and bare hostnames, or there is some other mismatch between `node.name` and
|
|
`cluster.initial_master_nodes`, then the cluster will not form successfully and
|
|
you will see log messages like the following.
|
|
|
|
[source,text]
|
|
--------------------------------------------------
|
|
[master-a.example.com] master not discovered yet, this node has
|
|
not previously joined a bootstrapped (v7+) cluster, and this
|
|
node must discover master-eligible nodes [master-a, master-b] to
|
|
bootstrap a cluster: have discovered [{master-b.example.com}{...
|
|
--------------------------------------------------
|
|
|
|
This message shows the node names `master-a.example.com` and
|
|
`master-b.example.com` as well as the `cluster.initial_master_nodes` entries
|
|
`master-a` and `master-b`, and it is clear from this message that they do not
|
|
match exactly.
|
|
|
|
==================================================
|
|
|
|
[float]
|
|
==== Choosing a cluster name
|
|
|
|
The <<cluster.name,`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.
|
|
|
|
[float]
|
|
==== Auto-bootstrapping in development mode
|
|
|
|
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 <<modules-discovery-bootstrap-cluster,section on cluster bootstrapping>>:
|
|
|
|
* `discovery.seed_providers`
|
|
* `discovery.seed_hosts`
|
|
* `cluster.initial_master_nodes`
|
|
|
|
[NOTE]
|
|
==================================================
|
|
|
|
[[modules-discovery-bootstrap-cluster-joining]] If you start an {es} node
|
|
without configuring these settings then it will start up in development mode and
|
|
auto-bootstrap itself into a new cluster. If you start some {es} nodes on
|
|
different hosts then by default they will not discover each other and will form
|
|
a different cluster on each host. {es} will not merge separate clusters together
|
|
after they have formed, even if you subsequently try and configure all the nodes
|
|
into a single cluster. This is because there is no way to merge these separate
|
|
clusters together without a risk of data loss. You can tell that you have formed
|
|
separate clusters by checking the cluster UUID reported by `GET /` on each node.
|
|
If you intended to form a single cluster then you should start again:
|
|
|
|
* Take a <<modules-snapshots,snapshot>> of each of the single-host clusters if
|
|
you do not want to lose any data that they hold. Note that each cluster must
|
|
use its own snapshot repository.
|
|
* Shut down all the nodes.
|
|
* Completely wipe each node by deleting the contents of their
|
|
<<data-path,data folders>>.
|
|
* Configure `cluster.initial_master_nodes` as described above.
|
|
* Restart all the nodes and verify that they have formed a single cluster.
|
|
* <<modules-snapshots,Restore>> any snapshots as required.
|
|
|
|
==================================================
|