[[indices-aliases]]
== Index Aliases

APIs in elasticsearch accept an index name when working against a
specific index, and several indices when applicable. The index aliases
API allow to alias an index with a name, with all APIs automatically
converting the alias name to the actual index name. An alias can also be
mapped to more than one index, and when specifying it, the alias will
automatically expand to the aliases indices. An alias can also be
associated with a filter that will automatically be applied when
searching, and routing values.

Here is a sample of associating the alias `alias1` with index `test1`:

[source,js]
--------------------------------------------------
curl -XPOST 'http://localhost:9200/_aliases' -d '
{
    "actions" : [
        { "add" : { "index" : "test1", "alias" : "alias1" } }
    ]
}'
--------------------------------------------------

An alias can also be removed, for example:

[source,js]
--------------------------------------------------
curl -XPOST 'http://localhost:9200/_aliases' -d '
{
    "actions" : [
        { "remove" : { "index" : "test1", "alias" : "alias1" } }
    ]
}'
--------------------------------------------------

Renaming an alias is a simple `remove` then `add` operation within the
same API. This operation is atomic, no need to worry about a short
period of time where the alias does not point to an index:

[source,js]
--------------------------------------------------
curl -XPOST 'http://localhost:9200/_aliases' -d '
{
    "actions" : [
        { "remove" : { "index" : "test1", "alias" : "alias1" } },
        { "add" : { "index" : "test1", "alias" : "alias2" } }
    ]
}'
--------------------------------------------------

Associating an alias with more than one index are simply several `add`
actions:

[source,js]
--------------------------------------------------
curl -XPOST 'http://localhost:9200/_aliases' -d '
{
    "actions" : [
        { "add" : { "index" : "test1", "alias" : "alias1" } },
        { "add" : { "index" : "test2", "alias" : "alias1" } }
    ]
}'
--------------------------------------------------

It is an error to index to an alias which points to more than one index.

[float]
[[filtered]]
=== Filtered Aliases

Aliases with filters provide an easy way to create different "views" of
the same index. The filter can be defined using Query DSL and is applied
to all Search, Count, Delete By Query and More Like This operations with
this alias. Here is an example:

[source,js]
--------------------------------------------------
curl -XPOST 'http://localhost:9200/_aliases' -d '
{
    "actions" : [
        {
            "add" : {
                 "index" : "test1",
                 "alias" : "alias2",
                 "filter" : { "term" : { "user" : "kimchy" } }
            }
        }
    ]
}'
--------------------------------------------------

[float]
[[aliases-routing]]
==== Routing

It is possible to associate routing values with aliases. This feature
can be used together with filtering aliases in order to avoid
unnecessary shard operations.

The following command creates a new alias `alias1` that points to index
`test`. After `alias1` is created, all operations with this alias are
automatically modified to use value `1` for routing:

[source,js]
--------------------------------------------------
curl -XPOST 'http://localhost:9200/_aliases' -d '
{
    "actions" : [
        {
            "add" : {
                 "index" : "test",
                 "alias" : "alias1",
                 "routing" : "1"
            }
        }
    ]
}'
--------------------------------------------------

It's also possible to specify different routing values for searching
and indexing operations:

[source,js]
--------------------------------------------------
curl -XPOST 'http://localhost:9200/_aliases' -d '
{
    "actions" : [
        {
            "add" : {
                 "index" : "test",
                 "alias" : "alias2",
                 "search_routing" : "1,2",
                 "index_routing" : "2"
            }
        }
    ]
}'
--------------------------------------------------

As shown in the example above, search routing may contain several values
separated by comma. Index routing can contain only a single value.

If an operation that uses routing alias also has a routing parameter, an
intersection of both alias routing and routing specified in the
parameter is used. For example the following command will use "2" as a
routing value:

[source,js]
--------------------------------------------------
curl -XGET 'http://localhost:9200/alias2/_search?q=user:kimchy&routing=2,3'
--------------------------------------------------

[float]
[[alias-adding]]
=== Add a single index alias

There is also an api to add a single index alias, with options: 

[horizontal]
`index`::   The index to alias refers to. This is a required option. 
`alias`::   The name of the alias. This is a required option. 
`routing`:: An optional routing that can be associated with an alias. 
`filter`::  An optional filter that can be associated with an alias.

The rest endpoint is: `/{index}/_alias/{alias}`.

[float]
==== Examples:

Adding time based alias:

[source,js]
--------------------------------------------------
curl -XPUT 'localhost:9200/logs_201305/_alias/2013'
--------------------------------------------------

Adding user alias:

[source,js]
--------------------------------------------------
curl -XPUT 'localhost:9200/users/_alias/user_12' -d '{
        "routing" : "12",
    "filter" : {
        "term" : {
            "user_id" : 12
        }
    }       
}'
--------------------------------------------------

[float]
[[deleting]]
=== Delete a single index alias

Th API to delete a single index alias, has options: 

[horizontal]
`index`:: The index the alias is in, the needs to be deleted. This is
          a required option. 
`alias`:: The name of the alias to delete. This is a required option.

The rest endpoint is: `/{index}/_alias/{alias}`. Example:

[source,js]
--------------------------------------------------
curl -XDELETE 'localhost:9200/users/_alias/user_12'
--------------------------------------------------

[float]
[[alias-retrieving]]
=== Retrieving existing aliases

The get index alias api allows to filter by
alias name and index name. This api redirects to the master and fetches
the requested index aliases, if available. This api only serialises the
found index aliases.

Possible options: 
[horizontal]
`index`::   

    The index name to get aliases for. Partially names are
    supported via wildcards, also multiple index names can be specified
    separated with a comma. Also the alias name for an index can be used. 

`alias`::   
    The name of alias to return in the response. Like the index
    option, this option supports wildcards and the option the specify
    multiple alias names separated by a comma.

`ignore_unavailable`::
    What to do is an specified index name doesn't
    exist. If set to `true` then those indices are ignored.

The rest endpoint is: `/{index}/_alias/{alias}`.

[float]
==== Examples:

All aliases for the index users:

[source,js]
--------------------------------------------------
curl -XGET 'localhost:9200/users/_alias/*'
--------------------------------------------------

Response:

[source,js]
--------------------------------------------------
 {
  "users" : {
    "aliases" : {
      "user_13" : {
        "filter" : {
          "term" : {
            "user_id" : 13
          }
        },
        "index_routing" : "13",
        "search_routing" : "13"
      },
      "user_14" : {
        "filter" : {
          "term" : {
            "user_id" : 14
          }
        },
        "index_routing" : "14",
        "search_routing" : "14"
      },
      "user_12" : {
        "filter" : {
          "term" : {
            "user_id" : 12
          }
        },
        "index_routing" : "12",
        "search_routing" : "12"
      }
    }
  }
}
--------------------------------------------------

All aliases with the name 2013 in any index:

[source,js]
--------------------------------------------------
curl -XGET 'localhost:9200/_alias/2013'
--------------------------------------------------

Response:

[source,js]
--------------------------------------------------
{
  "logs_201304" : {
    "aliases" : {
      "2013" : { }
    }
  },
  "logs_201305" : {
    "aliases" : {
      "2013" : { }
    }
  }
}
--------------------------------------------------

All aliases that start with 2013_01 in any index:

[source,js]
--------------------------------------------------
curl -XGET 'localhost:9200/_alias/2013_01*'
--------------------------------------------------

Response:

[source,js]
--------------------------------------------------
{
  "logs_20130101" : {
    "aliases" : {
      "2013_01" : { }
    }
  }
}
--------------------------------------------------

There is also a HEAD variant of the get indices aliases api to check if
index aliases exist. The indices aliases exists api supports the same
option as the get indices aliases api. Examples:

[source,js]
--------------------------------------------------
curl -XHEAD 'localhost:9200/_alias/2013'
curl -XHEAD 'localhost:9200/_alias/2013_01*'
curl -XHEAD 'localhost:9200/users/_alias/*'
--------------------------------------------------