OpenSearch/x-pack/docs/en/ilm/set-up-lifecycle-policy.asciidoc

[[set-up-lifecycle-policy]]
== Set up {ilm} policy

In order for an index to use an {ilm} policy to manage its lifecycle we must
first define a lifecycle policy for it to use. The following request creates
a policy called `my_policy` in Elasticsearch which we can later use to manage
our indexes.

[source,js]
------------------------
PUT _ilm/my_policy
{
  "policy": {
    "phases": {
      "hot": {
        "actions": {
          "rollover": {
            "max_size": "25GB" <1>
          }
        }
      },
      "delete": {
        "minimum_age": "30d",
        "actions": {
          "delete": {} <2>
        }
      }
    }
  }
}
------------------------ 
// CONSOLE
<1> Rollover the index when it reaches 25GB in size
<2> Delete the index when its 30 days old

{ilm} will manage an index using the policy defined in the 
`index.lifecycle.name` index setting. If this setting does not exist in the
settings for a particular index {ilm} will not manage that index.

To set the policy for an index there are two options:
1. Apply the policy to an index template and bootstrap creating the first index
2. Apply the policy to a new index in a create index request

=== Applying a policy to an index template

The `index.lifecycle.name` setting can be set in an index template so that it
is automatically applied to indexes matching the templates index pattern:

[source,js]
-----------------------
PUT _template/my_template
{
  "index_patterns": ["test-*"], <1>
  "settings": {
    "number_of_shards": 1,
    "number_of_replicas": 1,
    "index.lifecycle.name": "my_policy", <2>
    "index.lifecycle.rollover_alias": "test-alias"
  }
}
-----------------------
// CONSOLE
<1> This template will be applied to all indexes which have a name starting
with `test-`
<2> The template will set the policy to be used to `my_policy`

Now that a policy exists and is used in an index template we can create an
initial index which will be managed by our policy:

[source,js]
-----------------------
PUT test-000001
{
  "aliases": {
    "test-alias":{
      "is_write_index": true <1>
    }
  }
}
-----------------------
// CONSOLE
<1> Set this initial index to be the write index for this alias.

We can now write data to the `test-alias` alias. Because we have a rollover
action defined in our policy when the index grows larger than 25GB {ilm} will
create a new index and roll the alias over to use the new index automatically.

=== Apply a policy to a create index request

The `index.lifecycle.name` setting can be set on an individual create index
request so {ilm} immediately starts managing the index:

[source,js]
-----------------------
PUT test-index
{
  "settings": {
    "number_of_shards": 1,
    "number_of_replicas": 1,
    "index.lifecycle.name": "my_policy"
  }
}
-----------------------
// CONSOLE

IMPORTANT: Its recommended not to use the create index API with a policy that
defines a rollover action. If you do so, the new index as the result of the
rollover will not carry forward the policy. Always use index templates to
define policies with rollover actions.