[[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 index.


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

# Add > 1000 documents to logs-000001

POST /logs_write/_rollover <2>
{
  "conditions": {
    "max_age":   "7d",
    "max_docs":  1000
  }
}
--------------------------------------------------
// CONSOLE
// TEST[setup:huge_twitter]
// TEST[s/# Add > 1000 documents to logs-000001/POST _reindex?refresh\n{"source":{"index":"twitter"},"dest":{"index":"logs-000001"}}/]
<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-000002` 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]
--------------------------------------------------
{
  "acknowledged": true,
  "shards_acknowledged": true,
  "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
  }
}
--------------------------------------------------
// TESTRESPONSE
<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
{
  "conditions": {
    "max_age":   "7d",
    "max_docs":  1000
  }
}
--------------------------------------------------
// CONSOLE
// TEST[s/^/PUT my_old_index_name\nPUT my_old_index_name\/_alias\/my_alias\n/]

[float]
=== Using date math with the rolllover API

It can be useful to use <<date-math-index-names,date math>> to name the
rollover index according to the date that the index rolled over, e.g.
`logstash-2016.02.03`.  The rollover API supports date math, but requires the
index name to end with a dash followed by a number, e.g.
`logstash-2016.02.03-1` which is incremented every time the index is rolled
over. For instance:

[source,js]
--------------------------------------------------
# PUT /<logs-{now/d}-1> with URI encoding:
PUT /%3Clogs-%7Bnow%2Fd%7D-1%3E <1>
{
  "aliases": {
    "logs_write": {}
  }
}

PUT logs_write/log/1
{
  "message": "a dummy log"
}

# Wait for a day to pass

POST /logs_write/_rollover <2>
{
  "conditions": {
    "max_docs":   "1"
  }
}
--------------------------------------------------
// CONSOLE
// TEST[s/now/2016.10.31||/]
<1> Creates an index named with today's date (e.g.) `logs-2016.10.31-1`
<2> Rolls over to a new index with today's date, e.g. `logs-2016.10.31-000002` if run immediately, or `logs-2016.11.01-000002` if run after 24 hours

//////////////////////////

[source,js]
--------------------------------------------------
GET _alias
--------------------------------------------------
// CONSOLE
// TEST[continued]

[source,js]
--------------------------------------------------
{
  "logs-2016.10.31-000002": {
    "aliases": {
      "logs_write": {}
    }
  },
  "logs-2016.10.31-1": {
    "aliases": {}
  }
}
--------------------------------------------------
// TESTRESPONSE

//////////////////////////

These indices can then be referenced as described in the
<<date-math-index-names,date math documentation>>.  For example, to search
over indices created in the last three days, you could do the following:

[source,js]
--------------------------------------------------
# GET /<logs-{now/d}-*>,<logs-{now/d-1d}-*>,<logs-{now/d-2d}-*>/_search
GET /%3Clogs-%7Bnow%2Fd%7D-*%3E%2C%3Clogs-%7Bnow%2Fd-1d%7D-*%3E%2C%3Clogs-%7Bnow%2Fd-2d%7D-*%3E/_search
--------------------------------------------------
// CONSOLE
// TEST[continued]
// TEST[s/now/2016.10.31||/]

[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.