Refactor AliasOrIndex abstraction. (#54394)

Backport of #53982

In order to prepare the `AliasOrIndex` abstraction for the introduction of data streams,
the abstraction needs to be made more flexible, because currently it really can be only
an alias or an index.

* Renamed `AliasOrIndex` to `IndexAbstraction`.
* Introduced a `IndexAbstraction.Type` enum to indicate what a `IndexAbstraction` instance is.
* Replaced the `isAlias()` method that returns a boolean with the `getType()` method that returns the new Type enum.
* Moved `getWriteIndex()` up from the `IndexAbstraction.Alias` to the `IndexAbstraction` interface.
* Moved `getAliasName()` up from the `IndexAbstraction.Alias` to the `IndexAbstraction` interface and renamed it to `getName()`.
* Removed unnecessary casting to `IndexAbstraction.Alias` by just checking the `getType()` method.

Relates to #53100

plugins/examples/security-authorization-engine/src/main/java/org/elasticsearch/example/CustomAuthorizationEngine.java

@@ -20,7 +20,7 @@
 package org.elasticsearch.example;
 
 import org.elasticsearch.action.ActionListener;
-import org.elasticsearch.cluster.metadata.AliasOrIndex;
+import org.elasticsearch.cluster.metadata.IndexAbstraction;
 import org.elasticsearch.xpack.core.security.action.user.GetUserPrivilegesRequest;
 import org.elasticsearch.xpack.core.security.action.user.GetUserPrivilegesResponse;
 import org.elasticsearch.xpack.core.security.action.user.GetUserPrivilegesResponse.Indices;
@@ -90,7 +90,7 @@ public void authorizeClusterAction(RequestInfo requestInfo, AuthorizationInfo au
     @Override
     public void authorizeIndexAction(RequestInfo requestInfo, AuthorizationInfo authorizationInfo,
                                      AsyncSupplier<ResolvedIndices> indicesAsyncSupplier,
-                                     Map<String, AliasOrIndex> aliasOrIndexLookup,
+                                     Map<String, IndexAbstraction> aliasOrIndexLookup,
                                      ActionListener<IndexAuthorizationResult> listener) {
         if (isSuperuser(requestInfo.getAuthentication().getUser())) {
             indicesAsyncSupplier.getAsync(ActionListener.wrap(resolvedIndices -> {
@@ -109,9 +109,9 @@ public void authorizeIndexAction(RequestInfo requestInfo, AuthorizationInfo auth
 
     @Override
     public void loadAuthorizedIndices(RequestInfo requestInfo, AuthorizationInfo authorizationInfo,
-                                      Map<String, AliasOrIndex> aliasOrIndexLookup, ActionListener<List<String>> listener) {
+                                      Map<String, IndexAbstraction> indicesLookup, ActionListener<List<String>> listener) {
         if (isSuperuser(requestInfo.getAuthentication().getUser())) {
-            listener.onResponse(new ArrayList<>(aliasOrIndexLookup.keySet()));
+            listener.onResponse(new ArrayList<>(indicesLookup.keySet()));
         } else {
             listener.onResponse(Collections.emptyList());
         }

plugins/examples/security-authorization-engine/src/test/java/org/elasticsearch/example/CustomAuthorizationEngineTests.java

@@ -22,8 +22,8 @@
 import org.elasticsearch.Version;
 import org.elasticsearch.action.search.SearchRequest;
 import org.elasticsearch.action.support.PlainActionFuture;
-import org.elasticsearch.cluster.metadata.AliasOrIndex;
-import org.elasticsearch.cluster.metadata.AliasOrIndex.Index;
+import org.elasticsearch.cluster.metadata.IndexAbstraction;
+import org.elasticsearch.cluster.metadata.IndexAbstraction.Index;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.test.ESTestCase;
@@ -130,8 +130,8 @@ public void testAuthorizeClusterAction() {
 
     public void testAuthorizeIndexAction() {
         CustomAuthorizationEngine engine = new CustomAuthorizationEngine();
-        Map<String, AliasOrIndex> aliasOrIndexMap = new HashMap<>();
-        aliasOrIndexMap.put("index", new Index(IndexMetaData.builder("index")
+        Map<String, IndexAbstraction> indicesMap = new HashMap<>();
+        indicesMap.put("index", new Index(IndexMetaData.builder("index")
             .settings(Settings.builder().put("index.version.created", Version.CURRENT))
             .numberOfShards(1)
             .numberOfReplicas(0)
@@ -148,7 +148,7 @@ public void testAuthorizeIndexAction() {
             PlainActionFuture<IndexAuthorizationResult> resultFuture = new PlainActionFuture<>();
             engine.authorizeIndexAction(requestInfo, authzInfo,
                 listener -> listener.onResponse(new ResolvedIndices(Collections.singletonList("index"), Collections.emptyList())),
-                aliasOrIndexMap, resultFuture);
+                indicesMap, resultFuture);
             IndexAuthorizationResult result = resultFuture.actionGet();
             assertThat(result.isGranted(), is(true));
             assertThat(result.isAuditable(), is(true));
@@ -169,7 +169,7 @@ public void testAuthorizeIndexAction() {
             PlainActionFuture<IndexAuthorizationResult> resultFuture = new PlainActionFuture<>();
             engine.authorizeIndexAction(requestInfo, authzInfo,
                 listener -> listener.onResponse(new ResolvedIndices(Collections.singletonList("index"), Collections.emptyList())),
-                aliasOrIndexMap, resultFuture);
+                indicesMap, resultFuture);
             IndexAuthorizationResult result = resultFuture.actionGet();
             assertThat(result.isGranted(), is(false));
             assertThat(result.isAuditable(), is(true));

server/src/main/java/org/elasticsearch/action/admin/indices/rollover/MetaDataRolloverService.java

@@ -25,9 +25,9 @@
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.metadata.AliasAction;
 import org.elasticsearch.cluster.metadata.AliasMetaData;
-import org.elasticsearch.cluster.metadata.AliasOrIndex;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;
+import org.elasticsearch.cluster.metadata.IndexAbstraction;
 import org.elasticsearch.cluster.metadata.IndexTemplateMetaData;
 import org.elasticsearch.cluster.metadata.MetaData;
 import org.elasticsearch.cluster.metadata.MetaDataCreateIndexService;
@@ -79,9 +79,9 @@ public RolloverResult rolloverClusterState(ClusterState currentState, String ali
                                                boolean silent) throws Exception {
         final MetaData metaData = currentState.metaData();
         validate(metaData, aliasName);
-        final AliasOrIndex.Alias alias = (AliasOrIndex.Alias) metaData.getAliasAndIndexLookup().get(aliasName);
+        final IndexAbstraction alias = metaData.getIndicesLookup().get(aliasName);
         final IndexMetaData indexMetaData = alias.getWriteIndex();
-        final AliasMetaData aliasMetaData = indexMetaData.getAliases().get(alias.getAliasName());
+        final AliasMetaData aliasMetaData = indexMetaData.getAliases().get(alias.getName());
         final String sourceProvidedName = indexMetaData.getSettings().get(IndexMetaData.SETTING_INDEX_PROVIDED_NAME,
             indexMetaData.getIndex().getName());
         final String sourceIndexName = indexMetaData.getIndex().getName();
@@ -176,16 +176,16 @@ static void checkNoDuplicatedAliasInIndexTemplate(MetaData metaData, String roll
     }
 
     static void validate(MetaData metaData, String aliasName) {
-        final AliasOrIndex aliasOrIndex = metaData.getAliasAndIndexLookup().get(aliasName);
-        if (aliasOrIndex == null) {
+        final IndexAbstraction indexAbstraction = metaData.getIndicesLookup().get(aliasName);
+        if (indexAbstraction == null) {
             throw new IllegalArgumentException("source alias does not exist");
         }
-        if (aliasOrIndex.isAlias() == false) {
-            throw new IllegalArgumentException("source alias is a concrete index");
+        if (indexAbstraction.getType() != IndexAbstraction.Type.ALIAS) {
+            throw new IllegalArgumentException("source alias is a [" + indexAbstraction.getType().getDisplayName() +
+                "], but an [" + IndexAbstraction.Type.ALIAS.getDisplayName() + "] was expected");
         }
-        final AliasOrIndex.Alias alias = (AliasOrIndex.Alias) aliasOrIndex;
-        if (alias.getWriteIndex() == null) {
-            throw new IllegalArgumentException("source alias [" + alias.getAliasName() + "] does not point to a write index");
+        if (indexAbstraction.getWriteIndex() == null) {
+            throw new IllegalArgumentException("source alias [" + indexAbstraction.getName() + "] does not point to a write index");
         }
     }
 }

server/src/main/java/org/elasticsearch/action/bulk/TransportBulkAction.java

@@ -48,7 +48,7 @@
 import org.elasticsearch.cluster.ClusterStateObserver;
 import org.elasticsearch.cluster.block.ClusterBlockException;
 import org.elasticsearch.cluster.block.ClusterBlockLevel;
-import org.elasticsearch.cluster.metadata.AliasOrIndex;
+import org.elasticsearch.cluster.metadata.IndexAbstraction;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;
 import org.elasticsearch.cluster.metadata.IndexTemplateMetaData;
@@ -285,18 +285,16 @@ static boolean resolvePipelines(final DocWriteRequest<?> originalRequest, final
             IndexMetaData indexMetaData = metaData.indices().get(originalRequest.index());
             // check the alias for the index request (this is how normal index requests are modeled)
             if (indexMetaData == null && indexRequest.index() != null) {
-                AliasOrIndex indexOrAlias = metaData.getAliasAndIndexLookup().get(indexRequest.index());
-                if (indexOrAlias != null && indexOrAlias.isAlias()) {
-                    AliasOrIndex.Alias alias = (AliasOrIndex.Alias) indexOrAlias;
-                    indexMetaData = alias.getWriteIndex();
+                IndexAbstraction indexAbstraction = metaData.getIndicesLookup().get(indexRequest.index());
+                if (indexAbstraction != null) {
+                    indexMetaData = indexAbstraction.getWriteIndex();
                 }
             }
             // check the alias for the action request (this is how upserts are modeled)
             if (indexMetaData == null && originalRequest.index() != null) {
-                AliasOrIndex indexOrAlias = metaData.getAliasAndIndexLookup().get(originalRequest.index());
-                if (indexOrAlias != null && indexOrAlias.isAlias()) {
-                    AliasOrIndex.Alias alias = (AliasOrIndex.Alias) indexOrAlias;
-                    indexMetaData = alias.getWriteIndex();
+                IndexAbstraction indexAbstraction = metaData.getIndicesLookup().get(originalRequest.index());
+                if (indexAbstraction != null) {
+                    indexMetaData = indexAbstraction.getWriteIndex();
                 }
             }
             if (indexMetaData != null) {

server/src/main/java/org/elasticsearch/cluster/metadata/AliasOrIndex.java → server/src/main/java/org/elasticsearch/cluster/metadata/IndexAbstraction.java

@@ -16,7 +16,6 @@
  * specific language governing permissions and limitations
  * under the License.
  */
-
 package org.elasticsearch.cluster.metadata;
 
 import org.apache.lucene.util.SetOnce;
@@ -35,30 +34,77 @@
 import static org.elasticsearch.cluster.metadata.IndexMetaData.INDEX_HIDDEN_SETTING;
 
 /**
- * Encapsulates the  {@link IndexMetaData} instances of a concrete index or indices an alias is pointing to.
+ * An index abstraction is a reference to one or more concrete indices.
+ * An index abstraction has a unique name and encapsulates all the  {@link IndexMetaData} instances it is pointing to.
+ * Also depending on type it may refer to a single or many concrete indices and may or may not have a write index.
  */
-public interface AliasOrIndex {
+public interface IndexAbstraction {
+
+    /**
+     * @return the type of the index abstraction
+     */
+    Type getType();
 
     /**
-     * @return whether this an alias or concrete index
+     * @return the name of the index abstraction
      */
-    boolean isAlias();
+    String getName();
 
     /**
-     * @return All {@link IndexMetaData} of all concrete indices this alias is referring to
-     * or if this is a concrete index its {@link IndexMetaData}
+     * @return All {@link IndexMetaData} of all concrete indices this index abstraction is referring to.
      */
     List<IndexMetaData> getIndices();
 
     /**
-     * @return whether this alias/index is hidden or not
+     * A write index is a dedicated concrete index, that accepts all the new documents that belong to an index abstraction.
+     *
+     * A write index may also be a regular concrete index of a index abstraction and may therefore also be returned
+     * by {@link #getIndices()}. An index abstraction may also not have a dedicated write index.
+     *
+     * @return the write index of this index abstraction or
+     * <code>null</code> if this index abstraction doesn't have a write index.
+     */
+    @Nullable
+    IndexMetaData getWriteIndex();
+
+    /**
+     * @return whether this index abstraction is hidden or not
      */
     boolean isHidden();
 
+    /**
+     * An index abstraction type.
+     */
+    enum Type {
+
+        /**
+         * An index abstraction that refers to a single concrete index.
+         * This concrete index is also the write index.
+         */
+        CONCRETE_INDEX("concrete index"),
+
+        /**
+         * An index abstraction that refers to an alias.
+         * An alias typically refers to many concrete indices and
+         * may have a write index.
+         */
+        ALIAS("alias");
+
+        private final String displayName;
+
+        Type(String displayName) {
+            this.displayName = displayName;
+        }
+
+        public String getDisplayName() {
+            return displayName;
+        }
+    }
+
     /**
      * Represents an concrete index and encapsulates its {@link IndexMetaData}
      */
-    class Index implements AliasOrIndex {
+    class Index implements IndexAbstraction {
 
         private final IndexMetaData concreteIndex;
 
@@ -67,15 +113,25 @@ public Index(IndexMetaData indexMetaData) {
         }
 
         @Override
-        public boolean isAlias() {
-            return false;
+        public String getName() {
+            return concreteIndex.getIndex().getName();
+        }
+
+        @Override
+        public Type getType() {
+            return Type.CONCRETE_INDEX;
         }
 
         @Override
         public List<IndexMetaData> getIndices() {
             return Collections.singletonList(concreteIndex);
         }
 
+        @Override
+        public IndexMetaData getWriteIndex() {
+            return concreteIndex;
+        }
+
         @Override
         public boolean isHidden() {
             return INDEX_HIDDEN_SETTING.get(concreteIndex.getSettings());
@@ -85,7 +141,7 @@ public boolean isHidden() {
     /**
      * Represents an alias and groups all {@link IndexMetaData} instances sharing the same alias name together.
      */
-    class Alias implements AliasOrIndex {
+    class Alias implements IndexAbstraction {
 
         private final String aliasName;
         private final List<IndexMetaData> referenceIndexMetaDatas;
@@ -100,11 +156,11 @@ public Alias(AliasMetaData aliasMetaData, IndexMetaData indexMetaData) {
         }
 
         @Override
-        public boolean isAlias() {
-            return true;
+        public Type getType() {
+            return Type.ALIAS;
         }
 
-        public String getAliasName() {
+        public String getName() {
             return aliasName;
         }
 
@@ -131,7 +187,7 @@ public boolean isHidden() {
          * and filters)
          */
         public Iterable<Tuple<String, AliasMetaData>> getConcreteIndexAndAliasMetaDatas() {
-            return () -> new Iterator<Tuple<String,AliasMetaData>>() {
+            return () -> new Iterator<Tuple<String, AliasMetaData>>() {
 
                 int index = 0;