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[[modules-gateway]]
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== Gateway
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The gateway module allows one to store the state of the cluster meta
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data across full cluster restarts. The cluster meta data mainly holds
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all the indices created with their respective (index level) settings and
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explicit type mappings.
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Each time the cluster meta data changes (for example, when an index is
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added or deleted), those changes will be persisted using the gateway.
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When the cluster first starts up, the state will be read from the
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gateway and applied.
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The gateway set on the node level will automatically control the index
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gateway that will be used. For example, if the `local` gateway is used,
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then automatically, each index created on the node will also use its own
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respective index level `local` gateway. In this case, if an index should
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not persist its state, it should be explicitly set to `none` (which is
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the only other value it can be set to).
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The default gateway used is the
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<<modules-gateway-local,local>> gateway.
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[float]
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[[recover-after]]
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=== Recovery After Nodes / Time
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In many cases, the actual cluster meta data should only be recovered
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after specific nodes have started in the cluster, or a timeout has
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passed. This is handy when restarting the cluster, and each node local
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index storage still exists to be reused and not recovered from the
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gateway (which reduces the time it takes to recover from the gateway).
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The `gateway.recover_after_nodes` setting (which accepts a number)
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controls after how many data and master eligible nodes within the
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cluster recovery will start. The `gateway.recover_after_data_nodes` and
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`gateway.recover_after_master_nodes` setting work in a similar fashion,
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except they consider only the number of data nodes and only the number
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of master nodes respectively. The `gateway.recover_after_time` setting
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(which accepts a time value) sets the time to wait till recovery happens
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once all `gateway.recover_after...nodes` conditions are met.
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The `gateway.expected_nodes` allows to set how many data and master
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eligible nodes are expected to be in the cluster, and once met, the
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`gateway.recover_after_time` is ignored and recovery starts.
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Setting `gateway.expected_nodes` also defaults `gateway.recovery_after_time` to `5m` added[1.3.0, before `expected_nodes`
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required `recovery_after_time` to be set]. The `gateway.expected_data_nodes` and `gateway.expected_master_nodes`
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settings are also supported. For example setting:
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[source,js]
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--------------------------------------------------
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gateway:
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recover_after_time: 5m
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expected_nodes: 2
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--------------------------------------------------
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In an expected 2 nodes cluster will cause recovery to start 5 minutes
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after the first node is up, but once there are 2 nodes in the cluster,
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recovery will begin immediately (without waiting).
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Note, once the meta data has been recovered from the gateway (which
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indices to create, mappings and so on), then this setting is no longer
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effective until the next full restart of the cluster.
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Operations are blocked while the cluster meta data has not been
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recovered in order not to mix with the actual cluster meta data that
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will be recovered once the settings has been reached.
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include::gateway/local.asciidoc[]
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