ILM: add frozen phase (#60983) (#61035)

This adds a frozen phase to ILM that will allow the execution of the
set_priority, unfollow, allocate, freeze and searchable_snapshot actions.

The frozen phase will be executed after the cold and before the delete phase.

(cherry picked from commit 6d01480)
Signed-off-by: Andrei Dan <andrei.dan@elastic.co>

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

@@ -2,7 +2,7 @@
 [[ilm-allocate]]
 === Allocate
 
-Phases allowed: warm, cold.
+Phases allowed: warm, cold, frozen.
 
 Updates the index settings to change which nodes are allowed to host the index shards
 and change the number of replicas.

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

@@ -2,7 +2,7 @@
 [[ilm-freeze]]
 === Freeze
 
-Phases allowed: cold.
+Phases allowed: cold, frozen.
 
 <<frozen-indices, Freezes>> an index to minimize its memory footprint.
 

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

@@ -2,7 +2,7 @@
 [[ilm-searchable-snapshot]]
 === Searchable snapshot
 
-Phases allowed: cold.
+Phases allowed: cold, frozen.
 
 Takes a snapshot of the managed index in the configured repository
 and mounts it as a searchable snapshot.

docs/reference/ilm/actions/ilm-set-priority.asciidoc

@@ -2,7 +2,7 @@
 [[ilm-set-priority]]
 === Set priority
 
-Phases allowed: hot, warm, cold.
+Phases allowed: hot, warm, cold, frozen.
 
 Sets the <<recovery-prioritization, priority>> of the index as
 soon as the policy enters the hot, warm, or cold phase. 

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

@@ -2,7 +2,7 @@
 [[ilm-unfollow]]
 === Unfollow
 
-Phases allowed: hot, warm, cold.
+Phases allowed: hot, warm, cold, frozen.
 
 Converts a {ref}/ccr-apis.html[{ccr-init}] follower index into a regular index. 
 This enables the shrink, rollover, and searchable snapshot actions

docs/reference/ilm/ilm-index-lifecycle.asciidoc

@@ -6,13 +6,16 @@
 <titleabbrev>Index lifecycle</titleabbrev>
 ++++
 
-{ilm-init} defines four index lifecycle _phases_: 
+{ilm-init} defines five index lifecycle _phases_:
 
 * **Hot**: The index is actively being updated and queried.
 * **Warm**: The index is no longer being updated but is still being queried.
 * **Cold**: The index is no longer being updated and is seldom queried. The
 information still needs to be searchable, but it's okay if those queries are
 slower.
+* **Frozen**: The index is no longer being updated and is seldom queried. The
+queries are performing longer-term analyses for which a slower response is
+acceptable.
 * **Delete**: The index is no longer needed and can safely be removed.
 
 An index's _lifecycle policy_ specifies which phases 
@@ -93,6 +96,14 @@ the rollover criteria, it could be 20 minutes before the rollover is complete.
 ifdef::permanently-unreleased-branch[]
   - <<ilm-searchable-snapshot, Searchable Snapshot>>
 endif::[]
+* Frozen
+  - <<ilm-set-priority-action,Set Priority>>
+  - <<ilm-unfollow-action,Unfollow>>
+  - <<ilm-allocate,Allocate>>
+  - <<ilm-freeze,Freeze>>
+ifdef::permanently-unreleased-branch[]
+  - <<ilm-searchable-snapshot, Searchable Snapshot>>
+endif::[]
 * Delete
   - <<ilm-wait-for-snapshot-action,Wait For Snapshot>>
   - <<ilm-delete,Delete>>

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ilm/TimeseriesLifecycleType.java

@@ -34,25 +34,30 @@ public class TimeseriesLifecycleType implements LifecycleType {
     static final String HOT_PHASE = "hot";
     static final String WARM_PHASE = "warm";
     static final String COLD_PHASE = "cold";
+    static final String FROZEN_PHASE = "frozen";
     static final String DELETE_PHASE = "delete";
-    static final List<String> VALID_PHASES = Arrays.asList(HOT_PHASE, WARM_PHASE, COLD_PHASE, DELETE_PHASE);
+    static final List<String> VALID_PHASES = Arrays.asList(HOT_PHASE, WARM_PHASE, COLD_PHASE, FROZEN_PHASE, DELETE_PHASE);
     static final List<String> ORDERED_VALID_HOT_ACTIONS = Arrays.asList(SetPriorityAction.NAME, UnfollowAction.NAME, RolloverAction.NAME,
         ForceMergeAction.NAME);
     static final List<String> ORDERED_VALID_WARM_ACTIONS = Arrays.asList(SetPriorityAction.NAME, UnfollowAction.NAME, ReadOnlyAction.NAME,
         AllocateAction.NAME, ShrinkAction.NAME, ForceMergeAction.NAME);
     static final List<String> ORDERED_VALID_COLD_ACTIONS = Arrays.asList(SetPriorityAction.NAME, UnfollowAction.NAME, AllocateAction.NAME,
         FreezeAction.NAME, SearchableSnapshotAction.NAME);
+    static final List<String> ORDERED_VALID_FROZEN_ACTIONS = Arrays.asList(SetPriorityAction.NAME, UnfollowAction.NAME, AllocateAction.NAME,
+        FreezeAction.NAME, SearchableSnapshotAction.NAME);
     static final List<String> ORDERED_VALID_DELETE_ACTIONS = Arrays.asList(WaitForSnapshotAction.NAME, DeleteAction.NAME);
     static final Set<String> VALID_HOT_ACTIONS = Sets.newHashSet(ORDERED_VALID_HOT_ACTIONS);
     static final Set<String> VALID_WARM_ACTIONS = Sets.newHashSet(ORDERED_VALID_WARM_ACTIONS);
     static final Set<String> VALID_COLD_ACTIONS = Sets.newHashSet(ORDERED_VALID_COLD_ACTIONS);
+    static final Set<String> VALID_FROZEN_ACTIONS = Sets.newHashSet(ORDERED_VALID_FROZEN_ACTIONS);
     static final Set<String> VALID_DELETE_ACTIONS = Sets.newHashSet(ORDERED_VALID_DELETE_ACTIONS);
     private static Map<String, Set<String>> ALLOWED_ACTIONS = new HashMap<>();
 
     static {
         ALLOWED_ACTIONS.put(HOT_PHASE, VALID_HOT_ACTIONS);
         ALLOWED_ACTIONS.put(WARM_PHASE, VALID_WARM_ACTIONS);
         ALLOWED_ACTIONS.put(COLD_PHASE, VALID_COLD_ACTIONS);
+        ALLOWED_ACTIONS.put(FROZEN_PHASE, VALID_FROZEN_ACTIONS);
         ALLOWED_ACTIONS.put(DELETE_PHASE, VALID_DELETE_ACTIONS);
     }
 
@@ -141,6 +146,9 @@ public List<LifecycleAction> getOrderedActions(Phase phase) {
             case COLD_PHASE:
                 return ORDERED_VALID_COLD_ACTIONS.stream().map(a -> actions.getOrDefault(a, null))
                     .filter(Objects::nonNull).collect(Collectors.toList());
+            case FROZEN_PHASE:
+                return ORDERED_VALID_FROZEN_ACTIONS.stream().map(a -> actions.getOrDefault(a, null))
+                    .filter(Objects::nonNull).collect(Collectors.toList());
             case DELETE_PHASE:
                 return ORDERED_VALID_DELETE_ACTIONS.stream().map(a -> actions.getOrDefault(a, null))
                     .filter(Objects::nonNull).collect(Collectors.toList());
@@ -162,6 +170,9 @@ public String getNextActionName(String currentActionName, Phase phase) {
         case COLD_PHASE:
             orderedActionNames = ORDERED_VALID_COLD_ACTIONS;
             break;
+        case FROZEN_PHASE:
+            orderedActionNames = ORDERED_VALID_FROZEN_ACTIONS;
+            break;
         case DELETE_PHASE:
             orderedActionNames = ORDERED_VALID_DELETE_ACTIONS;
             break;

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/ilm/LifecyclePolicyTests.java

@@ -105,6 +105,8 @@ public static LifecyclePolicy randomTimeseriesLifecyclePolicyWithAllPhases(@Null
                     return TimeseriesLifecycleType.VALID_WARM_ACTIONS;
                 case "cold":
                     return TimeseriesLifecycleType.VALID_COLD_ACTIONS;
+                case "frozen":
+                    return TimeseriesLifecycleType.VALID_FROZEN_ACTIONS;
                 case "delete":
                     return TimeseriesLifecycleType.VALID_DELETE_ACTIONS;
                 default:
@@ -161,6 +163,8 @@ public static LifecyclePolicy randomTimeseriesLifecyclePolicy(@Nullable String l
                     return TimeseriesLifecycleType.VALID_WARM_ACTIONS;
                 case "cold":
                     return TimeseriesLifecycleType.VALID_COLD_ACTIONS;
+                case "frozen":
+                    return TimeseriesLifecycleType.VALID_FROZEN_ACTIONS;
                 case "delete":
                     return TimeseriesLifecycleType.VALID_DELETE_ACTIONS;
                 default: