[ILM] Fix the migrate to tiers service and migrate action tiers configuration

docs/changelog/95934.yaml

@@ -0,0 +1,5 @@
+pr: 95934
+summary: "[ILM] Fix the migrate to tiers service and migrate action tiers configuration"
+area: ILM+SLM
+type: bug
+issues: []

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

@@ -31,10 +31,8 @@ to `data_cold,data_warm,data_hot`. This moves the index to nodes in the
 The migrate action is not allowed in the frozen phase. The frozen phase directly
 mounts the searchable snapshot using a
 <<tier-preference-allocation-filter, `index.routing.allocation.include._tier_preference`>>
-of `data_frozen,data_cold,data_warm,data_hot`. This moves the index to nodes in the
-<<frozen-tier, frozen tier>>. If there are no nodes in the frozen tier, it falls back to the
-<<cold-tier, cold>> tier, then the <<warm-tier, warm>> tier, then finally the <<hot-tier, hot>>
-tier.
+of `data_frozen`. This moves the index to nodes in the
+<<frozen-tier, frozen tier>>.
 
 The migrate action is not allowed in the hot phase.
 The initial index allocation is performed <<data-tier-allocation, automatically>>,

server/src/main/java/org/elasticsearch/cluster/routing/allocation/DataTier.java

@@ -100,10 +100,15 @@ public class DataTier {
         final Map<String, Settings> tmpSettings = new HashMap<>();
         for (int i = 0, ordered_frozen_to_hot_tiersSize = ORDERED_FROZEN_TO_HOT_TIERS.size(); i < ordered_frozen_to_hot_tiersSize; i++) {
             String tier = ORDERED_FROZEN_TO_HOT_TIERS.get(i);
-            final String prefTierString = String.join(",", ORDERED_FROZEN_TO_HOT_TIERS.subList(i, ORDERED_FROZEN_TO_HOT_TIERS.size()))
-                .intern();
-            tmp.put(tier, prefTierString);
-            tmpSettings.put(tier, Settings.builder().put(DataTier.TIER_PREFERENCE, prefTierString).build());
+            if (tier.equals(DATA_FROZEN)) {
+                tmp.put(tier, DATA_FROZEN);
+                tmpSettings.put(DATA_FROZEN, Settings.builder().put(DataTier.TIER_PREFERENCE, DATA_FROZEN).build());
+            } else {
+                final String prefTierString = String.join(",", ORDERED_FROZEN_TO_HOT_TIERS.subList(i, ORDERED_FROZEN_TO_HOT_TIERS.size()))
+                    .intern();
+                tmp.put(tier, prefTierString);
+                tmpSettings.put(tier, Settings.builder().put(DataTier.TIER_PREFERENCE, prefTierString).build());
+            }
         }
         PREFERENCE_TIER_CONFIGURATIONS = Map.copyOf(tmp);
         PREFERENCE_TIER_CONFIGURATION_SETTINGS = Map.copyOf(tmpSettings);

server/src/test/java/org/elasticsearch/cluster/routing/allocation/DataTierTests.java

@@ -28,6 +28,7 @@
 import java.util.concurrent.atomic.AtomicInteger;
 
 import static org.elasticsearch.cluster.routing.allocation.DataTier.DATA_COLD;
+import static org.elasticsearch.cluster.routing.allocation.DataTier.DATA_FROZEN;
 import static org.elasticsearch.cluster.routing.allocation.DataTier.DATA_HOT;
 import static org.elasticsearch.cluster.routing.allocation.DataTier.DATA_WARM;
 import static org.elasticsearch.cluster.routing.allocation.DataTier.getPreferredTiersConfiguration;
@@ -120,6 +121,7 @@ public void testGetPreferredTiersConfiguration() {
         assertThat(getPreferredTiersConfiguration(DATA_HOT), is(DATA_HOT));
         assertThat(getPreferredTiersConfiguration(DATA_WARM), is(DATA_WARM + "," + DATA_HOT));
         assertThat(getPreferredTiersConfiguration(DATA_COLD), is(DATA_COLD + "," + DATA_WARM + "," + DATA_HOT));
+        assertThat(getPreferredTiersConfiguration(DATA_FROZEN), is(DATA_FROZEN));
         IllegalArgumentException exception = expectThrows(IllegalArgumentException.class, () -> getPreferredTiersConfiguration("no_tier"));
         assertThat(exception.getMessage(), is("invalid data tier [no_tier]"));
     }

x-pack/plugin/ilm/src/test/java/org/elasticsearch/xpack/cluster/metadata/MetadataMigrateToDataTiersRoutingServiceTests.java

@@ -148,7 +148,7 @@ public void testMigrateIlmPolicyForIndexWithoutILMMetadata() {
         assertThat(migratedColdAllocateAction.getRequire().size(), is(0));
     }
 
-    public void testMigrateIlmPolicyFOrPhaseWithDeactivatedMigrateAction() {
+    public void testMigrateIlmPolicyForPhaseWithDeactivatedMigrateAction() {
         ShrinkAction shrinkAction = new ShrinkAction(2, null);
         AllocateAction warmAllocateAction = new AllocateAction(null, null, Map.of("data", "warm"), null, Map.of("rack", "rack1"));
 
@@ -511,7 +511,7 @@ public void testAllocateActionDefinesRoutingRules() {
     }
 
     public void testConvertAttributeValueToTierPreference() {
-        assertThat(convertAttributeValueToTierPreference("frozen"), is("data_frozen,data_cold,data_warm,data_hot"));
+        assertThat(convertAttributeValueToTierPreference("frozen"), is("data_frozen"));
         assertThat(convertAttributeValueToTierPreference("cold"), is("data_cold,data_warm,data_hot"));
         assertThat(convertAttributeValueToTierPreference("warm"), is("data_warm,data_hot"));
         assertThat(convertAttributeValueToTierPreference("hot"), is("data_hot"));
@@ -560,6 +560,26 @@ public void testMigrateIndices() {
             assertThat(migratedIndex.getSettings().get(TIER_PREFERENCE), is("data_warm,data_hot"));
         }
 
+        {
+            // test the migration of `include.data: frozen` configuration to the equivalent _tier_preference routing
+            IndexMetadata.Builder indexWithFrozenDataAttribute = IndexMetadata.builder("indexWithFrozenDataAttribute")
+                .settings(getBaseIndexSettings().put(DATA_ROUTING_INCLUDE_SETTING, "frozen"));
+            ClusterState state = ClusterState.builder(ClusterName.DEFAULT)
+                .metadata(Metadata.builder().put(indexWithFrozenDataAttribute))
+                .build();
+
+            Metadata.Builder mb = Metadata.builder(state.metadata());
+
+            List<String> migratedIndices = migrateIndices(mb, state, "data");
+            assertThat(migratedIndices.size(), is(1));
+            assertThat(migratedIndices.get(0), is("indexWithFrozenDataAttribute"));
+
+            ClusterState migratedState = ClusterState.builder(ClusterName.DEFAULT).metadata(mb).build();
+            IndexMetadata migratedIndex = migratedState.metadata().index("indexWithFrozenDataAttribute");
+            assertThat(migratedIndex.getSettings().get(DATA_ROUTING_INCLUDE_SETTING), nullValue());
+            assertThat(migratedIndex.getSettings().get(TIER_PREFERENCE), is("data_frozen"));
+        }
+
         {
             // since the index has a _tier_preference configuration the migrated index should still contain it and have ALL the `data`
             // attributes routing removed