[DOCS] Make ILM documentation data stream aware (elastic#58035) (elastic#58110)

Co-authored-by: James Rodewig <james.rodewig@elastic.co>
Co-authored-by: Lee Hinman <dakrone@users.noreply.github.com>
(cherry picked from commit 25cbbe5)
Signed-off-by: Andrei Dan <andrei.dan@elastic.co>

Author: 3 people

docs/reference/glossary.asciidoc

@@ -268,10 +268,15 @@ shard will never be started on the same node as its primary shard.
 --
 // tag::rollover-def[]
 // tag::rollover-def-short[]
-Redirect an alias to begin writing to a new index when the existing index reaches a certain age, number of docs, or size. 
+
+Creates a new index for a rollover target when the existing index reaches a certain size, number of docs, or age.
+A rollover target can be either an <<indices-aliases, index alias>> or a <<data-streams, data stream>>.
 // end::rollover-def-short[]
-The new index is automatically configured according to any matching <<glossary-index-template, index templates>>. 
-For example, if you're indexing log data, you might use rollover to create daily or weekly indices. 
+
+The new index is automatically configured according to any matching <<glossary-index-template,index templates>> or
+respectively, a <<indices-templates,composable index template>> if the rollover target is a
+<<data-streams, data stream>>.
+For example, if you're indexing log data, you might use rollover to create daily or weekly indices.
 See the {ref}/indices-rollover-index.html[rollover index API].
 // end::rollover-def[]
 --

docs/reference/ilm/actions/ilm-rollover.asciidoc

@@ -4,15 +4,20 @@
 
 Phases allowed: hot.
 
-Rolls an alias over to a new index when the existing index meets one of the rollover conditions.
+Rolls over a target to a new index when the existing index meets one of the rollover conditions.
 
-IMPORTANT: If the rollover action is used on a <<ccr-put-follow,follower index>>, 
+IMPORTANT: If the rollover action is used on a <<ccr-put-follow,follower index>>,
 policy execution waits until the leader index rolls over (or is
-<<skipping-rollover, otherwise marked complete>>), 
-then converts the follower index into a regular index with the 
+<<skipping-rollover, otherwise marked complete>>),
+then converts the follower index into a regular index with the
 <<ilm-unfollow-action, Unfollow action>>.
 
-For a managed index to be rolled over: 
+A rollover target can be a <<data-streams, data stream>> or an <<indices-aliases, index alias>>.
+When targeting a data stream, the new index becomes the data stream's
+<<data-stream-write-index,write index>> and its generation is incremented.
+
+To roll over an <<indices-aliases, index alias>>, the alias and its write index
+must meet the following conditions:
 
 * The index name must match the pattern '^.*-\\d+$', for example (`my_index-000001`).
 * The `index.lifecycle.rollover_alias` must be configured as the alias to roll over. 

docs/reference/ilm/actions/ilm-searchable-snapshot.asciidoc

@@ -6,6 +6,18 @@ Phases allowed: cold.
 
 Takes a snapshot of the managed index in the configured repository
 and mounts it as a searchable snapshot.
+If the managed index is part of a <<data-streams, data stream>>,
+the mounted index replaces the original index in the data stream.
+
+[NOTE]
+This action cannot be performed on a data stream's write index. Attempts to do
+so will fail. To convert the index to a searchable snapshot, first
+<<manually-roll-over-a-data-stream,manually roll over>> the data stream. This
+creates a new write index. Because the index is no longer the stream's write
+index, the action can then convert it to a searchable snapshot.
+Using a policy that makes use of the <<ilm-rollover, rollover>> action
+in the hot phase will avoid this situation and the need for a manual rollover for future
+managed indices.
 
 By default, this snapshot is deleted by the <<ilm-delete-action, delete action>> in the delete phase.
 To keep the snapshot, set `delete_searchable_snapshot` to `false` in the delete action.

docs/reference/ilm/actions/ilm-shrink.asciidoc

@@ -21,6 +21,19 @@ policy execution waits until the leader index rolls over (or is
 then converts the follower index into a regular index with the 
 <<ilm-unfollow-action,the Unfollow action>> before performing the shrink operation.
 
+If the managed index is part of a <<data-streams, data stream>>,
+the shrunken index replaces the original index in the data stream.
+
+[NOTE]
+This action cannot be performed on a data stream's write index. Attempts to do
+so will fail. To shrink the index, first
+<<manually-roll-over-a-data-stream,manually roll over>> the data stream. This
+creates a new write index. Because the index is no longer the stream's write
+index, the action can resume shrinking it.
+Using a policy that makes use of the <<ilm-rollover, rollover>> action
+in the hot phase will avoid this situation and the need for a manual rollover for future
+managed indices.
+
 [[ilm-shrink-options]]
 ==== Shrink options
 `number_of_shards`::
@@ -48,4 +61,4 @@ PUT _ilm/policy/my_policy
     }
   }
 }
---------------------------------------------------
+--------------------------------------------------