59 lines
2.2 KiB
Plaintext
59 lines
2.2 KiB
Plaintext
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[[discovery-settings]]
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=== Discovery settings
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Elasticsearch uses a custom discovery implementation called "Zen Discovery" for
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node-to-node clustering and master election. There are two important discovery
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settings that should be configured before going to production.
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[float]
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[[unicast.hosts]]
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==== `discovery.zen.ping.unicast.hosts`
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Out of the box, without any network configuration, Elasticsearch will bind to
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the available loopback addresses and will scan ports 9300 to 9305 to try to
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connect to other nodes running on the same server. This provides an auto-
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clustering experience without having to do any configuration.
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When the moment comes to form a cluster with nodes on other servers, you have to
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provide a seed list of other nodes in the cluster that are likely to be live and
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contactable. This can be specified as follows:
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[source,yaml]
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--------------------------------------------------
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discovery.zen.ping.unicast.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.tcp.port` if not specified.
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<2> A hostname that resolves to multiple IP addresses will try all resolved
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addresses.
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[float]
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[[minimum_master_nodes]]
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==== `discovery.zen.minimum_master_nodes`
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To prevent data loss, it is vital to configure the
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`discovery.zen.minimum_master_nodes` setting so that each master-eligible node
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knows the _minimum number of master-eligible nodes_ that must be visible in
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order to form a cluster.
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Without this setting, a cluster that suffers a network failure is at risk of
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having the cluster split into two independent clusters -- a split brain -- which
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will lead to data loss. A more detailed explanation is provided in
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<<split-brain>>.
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To avoid a split brain, this setting should be set to a _quorum_ of
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master-eligible nodes:
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(master_eligible_nodes / 2) + 1
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In other words, if there are three master-eligible nodes, then minimum master
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nodes should be set to `(3 / 2) + 1` or `2`:
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[source,yaml]
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--------------------------------------------------
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discovery.zen.minimum_master_nodes: 2
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--------------------------------------------------
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