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Shard Allocation Filtering

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Shard Allocation Filtering

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Shard allocation filtering allows you to specify which nodes are allowed to host the shards of a particular index.

The per-index shard allocation filters explained below work in conjunction with the cluster-wide allocation filters explained in Cluster Level Shard Allocation.

It is possible to assign arbitrary metadata attributes to each node at startup. For instance, nodes could be assigned a rack and a group attribute as follows:

bin/elasticsearch --node.rack rack1 --node.size big

These attribute settings can also be specified in the elasticsearch.yml config file.

These metadata attributes can be used with the index.routing.allocation.* settings to allocate an index to a particular group of nodes. For instance, we can move the index test to either big or medium nodes as follows:

PUT test/_settings
{
  "index.routing.allocation.include.size": "big,medium"
}

Alternatively, we can move the index test away from the small nodes with an exclude rule:

PUT test/_settings
{
  "index.routing.allocation.exclude.size": "small"
}

Multiple rules can be specified, in which case all conditions must be satisfied. For instance, we could move the index test to big nodes in rack1 with the following:

PUT test/_settings
{
  "index.routing.allocation.include.size": "big",
  "index.routing.allocation.include.rack": "rack1"
}

If some conditions cannot be satisfied then shards will not be moved.

The following settings are dynamic, allowing live indices to be moved from one set of nodes to another:

index.routing.allocation.include.{attribute}: Assign the index to a node whose {attribute} has at least one of the comma-separated values.
index.routing.allocation.require.{attribute}: Assign the index to a node whose {attribute} has all of the comma-separated values.
index.routing.allocation.exclude.{attribute}: Assign the index to a node whose {attribute} has none of the comma-separated values.

These special attributes are also supported:

`_name`	Match nodes by node name
`_host_ip`	Match nodes by host IP address (IP associated with hostname)
`_publish_ip`	Match nodes by publish IP address
`_ip`	Match either `_host_ip` or `_publish_ip`
`_host`	Match nodes by hostname

All attribute values can be specified with wildcards, eg:

PUT test/_settings
{
  "index.routing.allocation.include._ip": "192.168.2.*"
}

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