131 lines
6.2 KiB
Plaintext
131 lines
6.2 KiB
Plaintext
[[modules-discovery-bootstrap-cluster]]
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=== Bootstrapping a cluster
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Starting an Elasticsearch cluster for the very first time requires the initial
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set of <<master-node,master-eligible nodes>> to be explicitly defined on one or
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more of the master-eligible nodes in the cluster. This is known as _cluster
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bootstrapping_. This is only required the very first time the cluster starts
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up: nodes that have already joined a cluster store this information in their
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data folder and freshly-started nodes that are joining an existing cluster
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obtain this information from the cluster's elected master.
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The initial set of master-eligible nodes is defined in the
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<<initial_master_nodes,`cluster.initial_master_nodes` setting>>. This is a list
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of the <<node.name,node names>> or IP addresses of the master-eligible nodes in
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the new cluster. If you do not configure `node.name` then it is set to the
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node's hostname, so in this case you can use hostnames in
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`cluster.initial_master_nodes` too.
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When you start a master-eligible node, you can provide this setting on the
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command line or in the `elasticsearch.yml` file. After the cluster has formed,
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this setting is no longer required and is ignored. It need not be set on
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master-ineligible nodes, nor on master-eligible nodes that are started to join
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an existing cluster. Note that master-eligible nodes should use storage that
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persists across restarts. If they do not, and `cluster.initial_master_nodes` is
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set, and a full cluster restart occurs, then another brand-new cluster will
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form and this may result in data loss.
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It is technically sufficient to set `cluster.initial_master_nodes` on a single
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master-eligible node in the cluster, and only to mention that single node in the
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setting's value, but this provides no fault tolerance before the cluster has
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fully formed. It is therefore better to bootstrap using at least three
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master-eligible nodes, each with a `cluster.initial_master_nodes` setting
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containing all three nodes.
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WARNING: You must set `cluster.initial_master_nodes` to the same list of nodes
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on each node on which it is set in order to be sure that only a single cluster
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forms during bootstrapping and therefore to avoid the risk of data loss.
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For a cluster with 3 master-eligible nodes (with <<node.name,node names>>
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`master-a`, `master-b` and `master-c`) the configuration will look as follows:
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[source,yaml]
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--------------------------------------------------
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cluster.initial_master_nodes:
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- master-a
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- master-b
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- master-c
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--------------------------------------------------
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You can use a mix of IP addresses and node names too. If there is more than one
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Elasticsearch node with the same IP address then the transport port must also
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be given to specify exactly which node is meant:
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[source,yaml]
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--------------------------------------------------
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cluster.initial_master_nodes:
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- 10.0.10.101
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- 10.0.10.102:9300
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- 10.0.10.102:9301
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- master-node-hostname
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--------------------------------------------------
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Like all node settings, it is also possible to specify the initial set of master
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nodes on the command-line that is used to start Elasticsearch:
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[source,bash]
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--------------------------------------------------
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$ bin/elasticsearch -Ecluster.initial_master_nodes=master-a,master-b,master-c
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--------------------------------------------------
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[NOTE]
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==================================================
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[[modules-discovery-bootstrap-cluster-fqdns]] The node names used in the
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`cluster.initial_master_nodes` list must exactly match the `node.name`
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properties of the nodes. By default the node name is set to the machine's
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hostname which may or may not be fully-qualified depending on your system
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configuration. If each node name is a fully-qualified domain name such as
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`master-a.example.com` then you must use fully-qualified domain names in the
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`cluster.initial_master_nodes` list too; conversely if your node names are bare
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hostnames (without the `.example.com` suffix) then you must use bare hostnames
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in the `cluster.initial_master_nodes` list. If you use a mix of fully-qualifed
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and bare hostnames, or there is some other mismatch between `node.name` and
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`cluster.initial_master_nodes`, then the cluster will not form successfully and
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you will see log messages like the following.
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[source,text]
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--------------------------------------------------
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[master-a.example.com] master not discovered yet, this node has
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not previously joined a bootstrapped (v7+) cluster, and this
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node must discover master-eligible nodes [master-a, master-b] to
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bootstrap a cluster: have discovered [{master-b.example.com}{...
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--------------------------------------------------
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This message shows the node names `master-a.example.com` and
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`master-b.example.com` as well as the `cluster.initial_master_nodes` entries
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`master-a` and `master-b`, and it is clear from this message that they do not
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match exactly.
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==================================================
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[float]
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==== Choosing a cluster name
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The <<cluster.name,`cluster.name`>> setting enables you to create multiple
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clusters which are separated from each other. Nodes verify that they agree on
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their cluster name when they first connect to each other, and Elasticsearch
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will only form a cluster from nodes that all have the same cluster name. The
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default value for the cluster name is `elasticsearch`, but it is recommended to
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change this to reflect the logical name of the cluster.
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[float]
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==== Auto-bootstrapping in development mode
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If the cluster is running with a completely default configuration then it will
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automatically bootstrap a cluster based on the nodes that could be discovered to
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be running on the same host within a short time after startup. This means that
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by default it is possible to start up several nodes on a single machine and have
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them automatically form a cluster which is very useful for development
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environments and experimentation. However, since nodes may not always
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successfully discover each other quickly enough this automatic bootstrapping
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cannot be relied upon and cannot be used in production deployments.
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If any of the following settings are configured then auto-bootstrapping will not
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take place, and you must configure `cluster.initial_master_nodes` as described
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in the <<modules-discovery-bootstrap-cluster,section on cluster bootstrapping>>:
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* `discovery.seed_providers`
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* `discovery.seed_hosts`
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* `cluster.initial_master_nodes`
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