[[indices-rollover-index]]
== Rollover Index

The rollover index API rolls an alias over to a new index when the existing
index is considered to be too large or too old.

The API accepts a single alias name and a list of `conditions`.  The alias
must point to a single index only.  If the index satisfies the specified
conditions then a new index is created and the alias is switched to point to
the new alias.


[source,js]
--------------------------------------------------
PUT /logs-000001 <1>
{
  "aliases": {
    "logs_write": {}
  }
}

POST logs_write/_rollover <2>
{
  "conditions": {
    "max_age":   "7d",
    "max_docs":  1000
  }
}
--------------------------------------------------
// CONSOLE
<1> Creates an index called `logs-0000001` with the alias `logs_write`.
<2> If the index pointed to by `logs_write` was created 7 or more days ago, or
    contains 1,000 or more documents, then the `logs-0002` index is created
    and the `logs_write` alias is updated to point to `logs-000002`.

The above request might return the following response:

[source,js]
--------------------------------------------------
{
  "old_index": "logs-000001",
  "new_index": "logs-000002",
  "rolled_over": true, <1>
  "dry_run": false, <2>
  "conditions": { <3>
    "[max_age: 7d]": false,
    "[max_docs: 1000]": true
  }
}
--------------------------------------------------
 <1> Whether the index was rolled over.
 <2> Whether the rollover was dry run.
 <3> The result of each condition.

[float]
=== Naming the new index

If the name of the existing index ends with `-` and a number -- e.g.
`logs-000001` -- then the name of the new index will follow the same pattern,
incrementing the number (`logs-000002`). The number is zero-padded with a length
of 6, regardless of the old index name.

If the old name doesn't match this pattern then you must specify the name for
the new index as follows:

[source,js]
--------------------------------------------------
POST my_alias/_rollover/my_new_index_name
{...}
--------------------------------------------------

[float]
=== Defining the new index

The settings, mappings, and aliases for the new index are taken from any
matching <<indices-templates,index templates>>. Additionally, you can specify
`settings`, `mappings`, and `aliases` in the body of the request, just like the
<<indices-create-index,create index>> API. Values specified in the request 
override any values set in matching index templates. For example, the following
`rollover` request overrides the `index.number_of_shards` setting:

[source,js]
--------------------------------------------------
PUT /logs-000001
{
  "aliases": {
    "logs_write": {}
  }
}

POST logs_write/_rollover
{
  "conditions" : {
    "max_age": "7d",
    "max_docs": 1000
  },
  "settings": { 
    "index.number_of_shards": 2 
  }
}
--------------------------------------------------
// CONSOLE

[float]
=== Dry run

The rollover API supports `dry_run` mode, where request conditions can be
checked without performing the actual rollover:

[source,js]
--------------------------------------------------
PUT /logs-000001
{
  "aliases": {
    "logs_write": {}
  }
}

POST logs_write/_rollover?dry_run
{
  "conditions" : {
    "max_age": "7d",
    "max_docs": 1000
  }
}
--------------------------------------------------
// CONSOLE

[float]
=== Wait For Active Shards

Because the rollover operation creates a new index to rollover to, the 
<<create-index-wait-for-active-shards,wait for active shards>> setting on 
index creation applies to the rollover action as well.