[8.5] Implement repair functionality for aliases colliding with indices bug (#91993)

* Fix corrupted Metadata from index and alias having the same name (#91456)

This fixes a bug introduced in #87863
which added a Metadata copy constructor with separate name collision checks that
assumed index name and alias names were already validated in `IndexMetada`.
=> fixed corrupted states by actually adding the validation to `IndexMetadata`
to make it impossible to instantiate a broken `IndexMetadata` in the first place.

* Implement repair functionality for aliases colliding with indices bug (#91887)

Follow up to #91456 implementing an automated fix for indices corrupted in 8.5.

Author: original-brownbear

docs/changelog/91456.yaml

@@ -0,0 +1,5 @@
+pr: 91456
+summary: Fix corrupted Metadata from index and alias having the same name
+area: Cluster Coordination
+type: bug
+issues: []

server/src/main/java/org/elasticsearch/cluster/metadata/IndexMetadata.java

@@ -8,6 +8,8 @@
 
 package org.elasticsearch.cluster.metadata;
 
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
 import org.elasticsearch.Version;
 import org.elasticsearch.action.admin.indices.rollover.RolloverInfo;
 import org.elasticsearch.action.support.ActiveShardCount;
@@ -82,6 +84,8 @@
 
 public class IndexMetadata implements Diffable<IndexMetadata>, ToXContentFragment {
 
+    private static final Logger logger = LogManager.getLogger(IndexMetadata.class);
+
     public static final ClusterBlock INDEX_READ_ONLY_BLOCK = new ClusterBlock(
         5,
         "index read-only (api)",
@@ -1512,7 +1516,7 @@ public IndexMetadata apply(IndexMetadata part) {
             builder.rolloverInfos.putAllFromMap(rolloverInfos.apply(part.rolloverInfos));
             builder.system(isSystem);
             builder.timestampRange(timestampRange);
-            return builder.build();
+            return builder.build(true);
         }
     }
 
@@ -1573,7 +1577,7 @@ public static IndexMetadata readFrom(StreamInput in, @Nullable Function<String,
             builder.system(in.readBoolean());
         }
         builder.timestampRange(IndexLongFieldRange.readFrom(in));
-        return builder.build();
+        return builder.build(true);
     }
 
     /**
@@ -1903,6 +1907,11 @@ public Builder timestampRange(IndexLongFieldRange timestampRange) {
         }
 
         public IndexMetadata build() {
+            return build(false);
+        }
+
+        // package private for testing
+        IndexMetadata build(boolean repair) {
             /*
              * We expect that the metadata has been properly built to set the number of shards and the number of replicas, and do not rely
              * on the default values here. Those must have been set upstream.
@@ -2020,7 +2029,16 @@ public IndexMetadata build() {
             var aliasesMap = aliases.build();
             for (AliasMetadata alias : aliasesMap.values()) {
                 if (alias.alias().equals(index)) {
-                    throw new IllegalArgumentException("alias name [" + index + "] self-conflicts with index name");
+                    if (repair && indexCreatedVersion.equals(Version.V_8_5_0)) {
+                        var updatedBuilder = ImmutableOpenMap.builder(aliasesMap);
+                        final var brokenAlias = updatedBuilder.remove(index);
+                        final var fixedAlias = AliasMetadata.newAliasMetadata(brokenAlias, index + "-alias-corrupted-by-8-5");
+                        aliasesMap = updatedBuilder.fPut(fixedAlias.getAlias(), fixedAlias).build();
+                        logger.warn("Repaired corrupted alias with the same name as its index for [{}]", index);
+                        break;
+                    } else {
+                        throw new IllegalArgumentException("alias name [" + index + "] self-conflicts with index name");
+                    }
                 }
             }
 
@@ -2321,7 +2339,7 @@ public static IndexMetadata fromXContent(XContentParser parser, Map<String, Mapp
             assert settingsVersion : "settings version should be present for indices created on or after 6.5.0";
             assert indexCreatedVersion(builder.settings).before(Version.V_7_2_0) || aliasesVersion
                 : "aliases version should be present for indices created on or after 7.2.0";
-            return builder.build();
+            return builder.build(true);
         }
 
         /**
@@ -2433,7 +2451,7 @@ public static IndexMetadata legacyFromXContent(XContentParser parser) throws IOE
                 builder.putMapping(MappingMetadata.EMPTY_MAPPINGS); // just make sure it's not empty so that _source can be read
             }
 
-            IndexMetadata indexMetadata = builder.build();
+            IndexMetadata indexMetadata = builder.build(true);
             assert indexMetadata.getCreationVersion().isLegacyIndexVersion();
             assert indexMetadata.getCompatibilityVersion().isLegacyIndexVersion();
             return indexMetadata;

server/src/test/java/org/elasticsearch/cluster/metadata/IndexMetadataTests.java

@@ -46,6 +46,7 @@
 import static org.elasticsearch.cluster.metadata.IndexMetadata.parseIndexNameCounter;
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.hasKey;
 import static org.hamcrest.Matchers.is;
 
 public class IndexMetadataTests extends ESTestCase {
@@ -483,16 +484,40 @@ public void testLifeCyclePolicyName() {
     }
 
     public void testIndexAndAliasWithSameName() {
-        final IllegalArgumentException iae = expectThrows(
-            IllegalArgumentException.class,
-            () -> IndexMetadata.builder("index")
-                .settings(Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, Version.CURRENT))
-                .numberOfShards(1)
-                .numberOfReplicas(0)
-                .putAlias(AliasMetadata.builder("index").build())
-                .build()
-        );
-        assertEquals("alias name [index] self-conflicts with index name", iae.getMessage());
+        {
+            final IllegalArgumentException iae = expectThrows(
+                IllegalArgumentException.class,
+                () -> IndexMetadata.builder("index")
+                    .settings(Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, Version.CURRENT))
+                    .numberOfShards(1)
+                    .numberOfReplicas(0)
+                    .putAlias(AliasMetadata.builder("index").build())
+                    .build(randomBoolean())
+            );
+            assertEquals("alias name [index] self-conflicts with index name", iae.getMessage());
+        }
+        {
+            final IllegalArgumentException iae = expectThrows(
+                IllegalArgumentException.class,
+                () -> IndexMetadata.builder("index")
+                    .settings(Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, Version.V_8_5_0))
+                    .numberOfShards(1)
+                    .numberOfReplicas(0)
+                    .putAlias(AliasMetadata.builder("index").build())
+                    .build(false)
+            );
+            assertEquals("alias name [index] self-conflicts with index name", iae.getMessage());
+        }
+    }
+
+    public void testRepairIndexAndAliasWithSameName() {
+        final IndexMetadata indexMetadata = IndexMetadata.builder("index")
+            .settings(Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, Version.V_8_5_0))
+            .numberOfShards(1)
+            .numberOfReplicas(0)
+            .putAlias(AliasMetadata.builder("index").build())
+            .build(true);
+        assertThat(indexMetadata.getAliases(), hasKey("index-alias-corrupted-by-8-5"));
     }
 
     private static Settings indexSettingsWithDataTier(String dataTier) {