156 lines
7.0 KiB
Plaintext
156 lines
7.0 KiB
Plaintext
[[modules-discovery-hosts-providers]]
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=== Discovery
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Discovery is the process by which the cluster formation module finds other
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nodes with which to form a cluster. This process runs when you start an
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Elasticsearch node or when a node believes the master node failed and continues
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until the master node is found or a new master node is elected.
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This process starts with a list of _seed_ addresses from one or more
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<<built-in-hosts-providers,seed hosts providers>>, together with the addresses
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of any master-eligible nodes that were in the last-known cluster. The process
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operates in two phases: First, each node probes the seed addresses by
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connecting to each address and attempting to identify the node to which it is
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connected and to verify that it is master-eligible. Secondly, if successful, it
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shares with the remote node a list of all of its known master-eligible peers
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and the remote node responds with _its_ peers in turn. The node then probes all
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the new nodes that it just discovered, requests their peers, and so on.
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If the node is not master-eligible then it continues this discovery process
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until it has discovered an elected master node. If no elected master is
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discovered then the node will retry after `discovery.find_peers_interval` which
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defaults to `1s`.
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If the node is master-eligible then it continues this discovery process until
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it has either discovered an elected master node or else it has discovered
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enough masterless master-eligible nodes to complete an election. If neither of
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these occur quickly enough then the node will retry after
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`discovery.find_peers_interval` which defaults to `1s`.
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[[built-in-hosts-providers]]
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==== Seed hosts providers
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By default the cluster formation module offers two seed hosts providers to
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configure the list of seed nodes: a _settings_-based and a _file_-based seed
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hosts provider. It can be extended to support cloud environments and other
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forms of seed hosts providers via {plugins}/discovery.html[discovery plugins].
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Seed hosts providers are configured using the `discovery.seed_providers`
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setting, which defaults to the _settings_-based hosts provider. This setting
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accepts a list of different providers, allowing you to make use of multiple
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ways to find the seed hosts for your cluster.
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Each seed hosts provider yields the IP addresses or hostnames of the seed
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nodes. If it returns any hostnames then these are resolved to IP addresses
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using a DNS lookup. If a hostname resolves to multiple IP addresses then {es}
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tries to find a seed node at all of these addresses. If the hosts provider does
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not explicitly give the TCP port of the node by then, it will implicitly use the
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first port in the port range given by `transport.profiles.default.port`, or by
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`transport.port` if `transport.profiles.default.port` is not set. The number of
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concurrent lookups is controlled by
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`discovery.seed_resolver.max_concurrent_resolvers` which defaults to `10`, and
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the timeout for each lookup is controlled by `discovery.seed_resolver.timeout`
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which defaults to `5s`. Note that DNS lookups are subject to
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<<networkaddress-cache-ttl,JVM DNS caching>>.
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[float]
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[[settings-based-hosts-provider]]
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===== Settings-based seed hosts provider
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The settings-based seed hosts provider uses a node setting to configure a
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static list of the addresses of the seed nodes. These addresses can be given as
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hostnames or IP addresses; hosts specified as hostnames are resolved to IP
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addresses during each round of discovery.
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The list of hosts is set using the <<unicast.hosts,`discovery.seed_hosts`>>
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static setting. For example:
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[source,yaml]
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--------------------------------------------------
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discovery.seed_hosts:
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- 192.168.1.10:9300
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- 192.168.1.11 <1>
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- seeds.mydomain.com <2>
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--------------------------------------------------
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<1> The port will default to `transport.profiles.default.port` and fallback to
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`transport.port` if not specified.
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<2> If a hostname resolves to multiple IP addresses, {es} will attempt to
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connect to every resolved address.
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[float]
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[[file-based-hosts-provider]]
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===== File-based seed hosts provider
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The file-based seed hosts provider configures a list of hosts via an external
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file. {es} reloads this file when it changes, so that the list of seed nodes
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can change dynamically without needing to restart each node. For example, this
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gives a convenient mechanism for an {es} instance that is run in a Docker
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container to be dynamically supplied with a list of IP addresses to connect to
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when those IP addresses may not be known at node startup.
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To enable file-based discovery, configure the `file` hosts provider as follows
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in the `elasticsearch.yml` file:
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[source,yml]
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----------------------------------------------------------------
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discovery.seed_providers: file
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----------------------------------------------------------------
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Then create a file at `$ES_PATH_CONF/unicast_hosts.txt` in the format described
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below. Any time a change is made to the `unicast_hosts.txt` file the new
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changes will be picked up by {es} and the new hosts list will be used.
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Note that the file-based discovery plugin augments the unicast hosts list in
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`elasticsearch.yml`: if there are valid seed addresses in
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`discovery.seed_hosts` then {es} uses those addresses in addition to those
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supplied in `unicast_hosts.txt`.
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The `unicast_hosts.txt` file contains one node entry per line. Each node entry
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consists of the host (host name or IP address) and an optional transport port
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number. If the port number is specified, is must come immediately after the
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host (on the same line) separated by a `:`. If the port number is not
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specified, {es} will implicitly use the first port in the port range given by
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`transport.profiles.default.port`, or by `transport.port` if
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`transport.profiles.default.port` is not set.
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For example, this is an example of `unicast_hosts.txt` for a cluster with four
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nodes that participate in discovery, some of which are not running on the
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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 and are resolved by DNS as
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described above. IPv6 addresses must be given in brackets with the port, if
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needed, coming after the brackets.
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You can also add comments to this file. All comments must appear on their lines
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starting with `#` (i.e. comments cannot start in the middle of a line).
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[float]
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[[ec2-hosts-provider]]
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===== EC2 hosts provider
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The {plugins}/discovery-ec2.html[EC2 discovery plugin] adds a hosts provider
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that uses the https://github.com/aws/aws-sdk-java[AWS API] to find a list of
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seed nodes.
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[float]
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[[azure-classic-hosts-provider]]
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===== Azure Classic hosts provider
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The {plugins}/discovery-azure-classic.html[Azure Classic discovery plugin] adds
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a hosts provider that uses the Azure Classic API find a list of seed nodes.
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[float]
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[[gce-hosts-provider]]
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===== Google Compute Engine hosts provider
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The {plugins}/discovery-gce.html[GCE discovery plugin] adds a hosts provider
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that uses the GCE API find a list of seed nodes.
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