Documentation for file-based discovery plugin (#20462)
Documentation for file-based discovery plugin. Closes #20458
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Ali Beyad
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[[discovery-file]]
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=== File-Based Discovery Plugin
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The file-based discovery plugin uses a list of hosts/ports in a `unicast_hosts.txt` file
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in the `config/discovery-file` directory for unicast discovery.
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[[discovery-file-install]]
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[float]
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==== Installation
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This plugin can be installed using the plugin manager:
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[source,sh]
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----------------------------------------------------------------
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sudo bin/elasticsearch-plugin install discovery-file
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----------------------------------------------------------------
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The plugin must be installed on every node in the cluster, and each node must
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be restarted after installation. Note that installing the plugin will add a
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`discovery-file` directory to the `config` folder, and a default `unicast_hosts.txt`
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file that must be edited with the correct unicast hosts list before starting the node.
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[[discovery-file-remove]]
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[float]
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==== Removal
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The plugin can be removed with the following command:
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[source,sh]
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----------------------------------------------------------------
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sudo bin/elasticsearch-plugin remove discovery-file
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----------------------------------------------------------------
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The node must be stopped before removing the plugin.
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[[discovery-file-usage]]
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[float]
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==== Using the file-based discovery plugin
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The file-based discovery plugin provides the ability to specify the
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unicast hosts list through a simple `unicast_hosts.txt` file that can
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be dynamically updated at any time. The discovery type for this plugin
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is still the default `zen` plugin, so no changes are required to the
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`elasticsearch.yml` config file. This plugin simply provides a facility
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to supply the unicast hosts list for zen discovery through an external
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file that can be updated at any time by a side process.
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For example, this gives a convenient mechanism for an Elasticsearch instance
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that is run in docker containers to be dynamically supplied a list of IP
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addresses to connect to for zen discovery when those IP addresses may not be
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known at node startup.
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Note that the file-based discovery plugin is meant to augment the unicast
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hosts list in `elasticsearch.yml` (if specified), not replace it. Therefore,
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if there are valid unicast host entries in `discovery.zen.ping.unicast.hosts`,
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they will be used in addition to those supplied in `unicast_hosts.txt`.
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Anytime a change is made to the `unicast_hosts.txt` file, even as Elasticsearch
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continues to run, the new changes will be picked up by the plugin and the
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new hosts list will be used for the next pinging round for master election.
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Upon installation of the plugin, a default `unicast_hosts.txt` file will
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be found in the `$CONFIG_DIR/discovery-file` directory. This default file
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will contain some comments about what the file should contain. All comments
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for this file must appear on their lines starting with `#` (i.e. comments
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cannot start in the middle of a line).
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[[discovery-file-format]]
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[float]
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==== unicast_hosts.txt file format
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The format of the file is to specify one unicast host entry per line.
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Each unicast host entry consists of the host (host name or IP address) and
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an optional transport port number. If the port number is specified, is must
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come immediately after the host (on the same line) separated by a `:`.
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If the port number is not specified, a default value of 9300 is used.
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For example, this is an example of `unicast_hosts.txt` for a cluster with
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four nodes that participate in unicast discovery, some of which are not
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running on the default port:
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[source,txt]
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----------------------------------------------------------------
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10.10.10.5
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10.10.10.6:9305
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10.10.10.5:10005
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# an IPv6 address
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[2001:0db8:85a3:0000:0000:8a2e:0370:7334]:9301
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----------------------------------------------------------------
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Host names are allowed instead of IP addresses (similar to
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`discovery.zen.ping.unicast.hosts`), and IPv6 addresses must be
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specified in brackets with the port coming after the brackets.
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@ -21,6 +21,10 @@ The Azure Classic discovery plugin uses the Azure Classic API for unicast discov
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The Google Compute Engine discovery plugin uses the GCE API for unicast discovery.
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<<discovery-file,File-based discovery>>::
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The File-based discovery plugin allows providing the unicast hosts list through a dynamically updatable file.
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[float]
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==== Community contributed discovery plugins
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@ -37,3 +41,5 @@ include::discovery-azure-classic.asciidoc[]
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include::discovery-gce.asciidoc[]
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include::discovery-file.asciidoc[]
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