Allow readonly in the hot phase for ILM policies

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

@@ -2,10 +2,13 @@
 [[ilm-readonly]]
 === Read only
 
-Phases allowed: warm.
+Phases allowed: hot, warm.
 
 Makes the index <<index-blocks-read-only,read-only>>.
 
+To use the `readonly` action in the `hot` phase, the `rollover` action *must* be present.
+If no rollover action is configured, {ilm-init} will reject the policy.
+
 [[ilm-read-only-options]]
 ==== Options
 

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

@@ -78,6 +78,7 @@ the rollover criteria, it could be 20 minutes before the rollover is complete.
   - <<ilm-set-priority,Set Priority>>
   - <<ilm-unfollow,Unfollow>>
   - <<ilm-rollover,Rollover>>
+  - <<ilm-readonly,Read-Only>>
   - <<ilm-shrink,Shrink>>
   - <<ilm-forcemerge,Force Merge>>
 * Warm

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

@@ -40,7 +40,7 @@ public class TimeseriesLifecycleType implements LifecycleType {
     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> ORDERED_VALID_HOT_ACTIONS = Arrays.asList(SetPriorityAction.NAME, UnfollowAction.NAME, RolloverAction.NAME,
-        ShrinkAction.NAME, ForceMergeAction.NAME);
+        ReadOnlyAction.NAME, ShrinkAction.NAME, ForceMergeAction.NAME);
     static final List<String> ORDERED_VALID_WARM_ACTIONS = Arrays.asList(SetPriorityAction.NAME, UnfollowAction.NAME, ReadOnlyAction.NAME,
         AllocateAction.NAME, MigrateAction.NAME, ShrinkAction.NAME, ForceMergeAction.NAME);
     static final List<String> ORDERED_VALID_COLD_ACTIONS = Arrays.asList(SetPriorityAction.NAME, UnfollowAction.NAME, AllocateAction.NAME,
@@ -56,7 +56,8 @@ public class TimeseriesLifecycleType implements LifecycleType {
         COLD_PHASE, VALID_COLD_ACTIONS,
         DELETE_PHASE, VALID_DELETE_ACTIONS);
 
-    static final Set<String> HOT_ACTIONS_THAT_REQUIRE_ROLLOVER = Sets.newHashSet(ShrinkAction.NAME, ForceMergeAction.NAME);
+    static final Set<String> HOT_ACTIONS_THAT_REQUIRE_ROLLOVER = Sets.newHashSet(ReadOnlyAction.NAME, ShrinkAction.NAME,
+        ForceMergeAction.NAME);
 
     private TimeseriesLifecycleType() {
     }

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

@@ -406,7 +406,6 @@ public void testGetNextActionName() {
         assertInvalidAction("hot", "foo", new String[] { RolloverAction.NAME });
         assertInvalidAction("hot", AllocateAction.NAME, new String[] { RolloverAction.NAME });
         assertInvalidAction("hot", DeleteAction.NAME, new String[] { RolloverAction.NAME });
-        assertInvalidAction("hot", ReadOnlyAction.NAME, new String[] { RolloverAction.NAME });
 
         // Warm Phase
         assertNextActionName("warm", SetPriorityAction.NAME, UnfollowAction.NAME,

x-pack/plugin/ilm/qa/multi-node/src/javaRestTest/java/org/elasticsearch/xpack/ilm/TimeSeriesLifecycleActionsIT.java

@@ -433,7 +433,8 @@ public void testDeleteDuringSnapshot() throws Exception {
     }
 
     public void testReadOnly() throws Exception {
-        createIndexWithSettings(client(), index, alias, Settings.builder().put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1)
+        createIndexWithSettings(client(), index, alias, Settings.builder()
+            .put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1)
             .put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 0));
         createNewSingletonPolicy(client(), policy, "warm", new ReadOnlyAction());
         updatePolicy(index, policy);
@@ -444,6 +445,35 @@ public void testReadOnly() throws Exception {
         });
     }
 
+    public void testReadOnlyInTheHotPhase() throws Exception {
+        String originalIndex = index + "-000001";
+
+        // add a policy
+        Map<String, LifecycleAction> hotActions = Map.of(
+            RolloverAction.NAME, new RolloverAction(null, null, 1L),
+            ReadOnlyAction.NAME, new ReadOnlyAction());
+        Map<String, Phase> phases = Map.of(
+            "hot", new Phase("hot", TimeValue.ZERO, hotActions));
+        LifecyclePolicy lifecyclePolicy = new LifecyclePolicy(policy, phases);
+        Request createPolicyRequest = new Request("PUT", "_ilm/policy/" + policy);
+        createPolicyRequest.setJsonEntity("{ \"policy\":" + Strings.toString(lifecyclePolicy) + "}");
+        client().performRequest(createPolicyRequest);
+
+        // then create the index and index a document to trigger rollover
+        createIndexWithSettings(client(), originalIndex, alias, Settings.builder()
+            .put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1)
+            .put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 0)
+            .put("index.lifecycle.rollover_alias", alias)
+            .put("index.lifecycle.name", policy));
+        index(client(), originalIndex, "_id", "foo", "bar");
+
+        assertBusy(() -> {
+            Map<String, Object> settings = getOnlyIndexSettings(client(), originalIndex);
+            assertThat(getStepKeyForIndex(client(), originalIndex), equalTo(PhaseCompleteStep.finalStep("hot").getKey()));
+            assertThat(settings.get(IndexMetadata.INDEX_BLOCKS_WRITE_SETTING.getKey()), equalTo("true"));
+        });
+    }
+
     public void forceMergeActionWithCodec(String codec) throws Exception {
         createIndexWithSettings(client(), index, alias, Settings.builder().put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1)
             .put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 0));

x-pack/plugin/ilm/qa/rest/src/yamlRestTest/resources/rest-api-spec/test/ilm/10_basic.yml

@@ -258,3 +258,21 @@ setup:
                }
              }
            }
+
+  - do:
+      catch: bad_request
+      ilm.put_lifecycle:
+        policy: "my_invalid_lifecycle"
+        body: |
+           {
+             "policy": {
+               "phases": {
+                 "hot": {
+                   "min_age": "0s",
+                   "actions": {
+                     "readonly": {}
+                   }
+                 }
+               }
+             }
+           }