Rollover min_* conditions docs and highlight (#89434)

docs/changelog/83345.yaml

@@ -3,3 +3,33 @@ summary: Add min_* conditions to rollover
 area: ILM+SLM
 type: enhancement
 issues: []
+highlight:
+   title: Minimum conditions for the rollover API and ILM actions
+   body: |-
+     The rollover API and ILM actions now support minimum conditions for rollover.
+
+     Minimum conditions prevent rollover from occuring until they are met. That is, an index
+     will rollover once one or more max conditions are satisfied and all min conditions are satisfied.
+
+     As an example, the following ILM policy would roll an index over if it is at least 7 days old or
+     at least 100 gigabytes, but only as long as the index is not empty.
+
+     ```
+     PUT _ilm/policy/my_policy
+     {
+       "policy": {
+         "phases": {
+           "hot": {
+             "actions": {
+               "rollover" : {
+                 "max_age": "7d",
+                 "max_size": "100gb",
+                 "min_docs": 1
+               }
+             }
+           }
+         }
+       }
+     }
+     ```
+   notable: true

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

@@ -4,7 +4,8 @@
 
 Phases allowed: hot.
 
-Rolls over a target to a new index when the existing index meets one or more of the rollover conditions.
+Rolls over a target to a new index when the existing index satisfies
+the specified rollover conditions.
 
 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
@@ -45,8 +46,11 @@ PUT my-index-000001
 [[ilm-rollover-options]]
 ==== Options
 
-You must specify at least one rollover condition.
-An empty rollover action is invalid.
+A rollover action must specify at least one max_* condition, it may include zero
+or more min_* conditions. An empty rollover action is invalid.
+
+The index will rollover once any max_* condition is satisfied and all
+min_* conditions are satisfied.
 
 // tag::rollover-conditions[]
 `max_age`::
@@ -90,6 +94,32 @@ replicas are ignored.
 +
 TIP: To see the current shard docs, use the <<cat-shards, _cat shards>> API.
 The `docs` value shows the number of documents each shard.
+
+`min_age`::
+(Optional,  <<time-units, time units>>)
+Prevents rollover until after the minimum elapsed time from index creation is reached.
+See notes on `max_age`.
+
+`min_docs`::
+(Optional, integer)
+Prevents rollover until after the specified minimum number of documents is reached.
+See notes on `max_docs`.
+
+`min_size`::
+(Optional, <<byte-units, byte units>>)
+Prevents rollover until the index reaches a certain size.
+See notes on `max_size`.
+
+`min_primary_shard_size`::
+(Optional, <<byte-units, byte units>>)
+Prevents rollover until the largest primary shard in the index reaches a certain size.
+See notes on `max_primary_shard_size`.
+
+`min_primary_shard_docs`::
+(Optional, integer)
+Prevents rollover until the largest primary shard in the index reaches a certain number of documents.
+See notes on `max_primary_shard_docs`.
+
 // end::rollover-conditions[]
 
 [[ilm-rollover-ex]]
@@ -109,7 +139,7 @@ PUT _ilm/policy/my_policy
       "hot": {
         "actions": {
           "rollover" : {
-            "max_primary_shard_size": "50GB"
+            "max_primary_shard_size": "50gb"
           }
         }
       }
@@ -132,7 +162,7 @@ PUT _ilm/policy/my_policy
       "hot": {
         "actions": {
           "rollover" : {
-            "max_size": "100GB"
+            "max_size": "100gb"
           }
         }
       }
@@ -214,8 +244,9 @@ PUT _ilm/policy/my_policy
 ===== Roll over using multiple conditions
 
 When you specify multiple rollover conditions,
-the index is rolled over when _any_ of the conditions are met.
-This example rolls the index over if it is at least 7 days old or at least 100 gigabytes.
+the index is rolled over when _any_ of the max_* and _all_ of the min_* conditions are met.
+This example rolls the index over if it is at least 7 days old or at least 100 gigabytes,
+but only as long as the index is not empty.
 
 [source,console]
 --------------------------------------------------
@@ -227,7 +258,35 @@ PUT _ilm/policy/my_policy
         "actions": {
           "rollover" : {
             "max_age": "7d",
-            "max_size": "100GB"
+            "max_size": "100gb",
+            "min_docs": 1
+          }
+        }
+      }
+    }
+  }
+}
+--------------------------------------------------
+
+[ilm-rollover-conditions-ex]]
+===== Roll over while maintaining shard sizes
+
+This example rolls the index over when the primary shard size is at least 50gb,
+or when the index is at least 30 days old, but only as long as a primary shard is at least 1gb.
+For low-volume indices, this prevents the creation of many small shards.
+
+[source,console]
+--------------------------------------------------
+PUT _ilm/policy/my_policy
+{
+  "policy": {
+    "phases": {
+      "hot": {
+        "actions": {
+          "rollover" : {
+            "max_primary_shard_size": "50gb",
+            "max_age": "30d",
+            "min_primary_shard_size": "1gb"
           }
         }
       }
@@ -254,7 +313,7 @@ PUT /_ilm/policy/rollover_policy
       "hot": {
         "actions": {
           "rollover": {
-            "max_size": "50GB"
+            "max_size": "50gb"
           }
         }
       },

docs/reference/ilm/index-rollover.asciidoc

@@ -43,7 +43,7 @@ On each rollover, the new index becomes the write index.
 === Automatic rollover
 
 {ilm-init} enables you to automatically roll over to a new index based
-on the index size, document count, or age. When a rollover is triggered, a new
+on conditions like the index size, document count, or age. When a rollover is triggered, a new
 index is created, the write alias is updated to point to the new index, and all
 subsequent updates are written to the new index.
 

docs/reference/indices/rollover-index.asciidoc

@@ -111,7 +111,7 @@ include::{es-repo-dir}/indices/create-index.asciidoc[tag=index-name-reqs]
 
 `dry_run`::
 (Optional, Boolean)
-If `true`, checks whether the current index matches one or more specified
+If `true`, checks whether the current index satisfies the specified
 `conditions` but does not perform a rollover. Defaults to `false`.
 
 include::{es-repo-dir}/rest-api/common-parms.asciidoc[tag=wait_for_active_shards]
@@ -132,10 +132,14 @@ include::{es-repo-dir}/indices/create-index.asciidoc[tag=aliases-props]
 `conditions`::
 (Optional, object)
 Conditions for the rollover. If specified, {es} only performs the rollover if
-the current index meets one or more of these conditions. If this parameter is
+the current index satisfies these conditions. If this parameter is
 not specified, {es} performs the rollover unconditionally.
 +
-IMPORTANT: To trigger a rollover, the current index must meet these conditions
+If conditions are specified, at least one of them must be a max_* condition.
+The index will rollover if any max_* condition is satisfied and all
+min_* conditions are satisfied.
++
+IMPORTANT: To trigger a rollover, the current index must satisfy these conditions
 at the time of the request. {es} does not monitor the index after the API
 response. To automate rollover, use {ilm-init}'s <<ilm-rollover,`rollover`>>
 instead.
@@ -197,7 +201,7 @@ conditions were specified, this is an empty object.
 ====
 `<condition>`::
 (Boolean) The key is each condition. The value is its result. If `true`, the
-index met the condition at rollover.
+index met the condition.
 ====
 
 [[rollover-index-api-example]]