[ML] Automatically rollover legacy .ml-anomalies indices (#120885)

Rollover legacy v87 .ml-anomalies indices and update the job aliases.
Anomaly detection requires read + write indices, this rollover ensures 
AD will continue to work after upgrading to 9

Author: davidkyle

docs/changelog/120885.yaml

@@ -0,0 +1,5 @@
+pr: 120885
+summary: Automatically rollover legacy .ml-anomalies indices
+area: Machine Learning
+type: upgrade
+issues: []

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/persistence/AnomalyDetectorsIndex.java

@@ -37,6 +37,10 @@ public static String jobResultsIndexPrefix() {
         return AnomalyDetectorsIndexFields.RESULTS_INDEX_PREFIX;
     }
 
+    public static String jobResultsIndexPattern() {
+        return AnomalyDetectorsIndexFields.RESULTS_INDEX_PREFIX + "*";
+    }
+
     /**
      * The name of the alias pointing to the indices where the job's results are stored
      * @param jobId Job Id
@@ -46,15 +50,26 @@ public static String jobResultsAliasedName(String jobId) {
         return AnomalyDetectorsIndexFields.RESULTS_INDEX_PREFIX + jobId;
     }
 
+    /**
+     * Extract the job Id from the alias name.
+     * If not an results index alias null is returned
+     * @param jobResultsAliasedName The alias
+     * @return The job Id
+     */
+    public static String jobIdFromAlias(String jobResultsAliasedName) {
+        if (jobResultsAliasedName.length() < AnomalyDetectorsIndexFields.RESULTS_INDEX_PREFIX.length()) {
+            return null;
+        }
+        return jobResultsAliasedName.substring(AnomalyDetectorsIndexFields.RESULTS_INDEX_PREFIX.length());
+    }
+
     /**
      * The name of the alias pointing to the write index for a job
      * @param jobId Job Id
      * @return The write alias
      */
     public static String resultsWriteAlias(String jobId) {
-        // ".write" rather than simply "write" to avoid the danger of clashing
-        // with the read alias of a job whose name begins with "write-"
-        return AnomalyDetectorsIndexFields.RESULTS_INDEX_PREFIX + ".write-" + jobId;
+        return AnomalyDetectorsIndexFields.RESULTS_INDEX_WRITE_PREFIX + jobId;
     }
 
     /**

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/persistence/AnomalyDetectorsIndexFields.java

@@ -11,6 +11,9 @@ public final class AnomalyDetectorsIndexFields {
     public static final String STATE_INDEX_PREFIX = ".ml-state";
 
     public static final String RESULTS_INDEX_PREFIX = ".ml-anomalies-";
+    // ".write" rather than simply "write" to avoid the danger of clashing
+    // with the read alias of a job whose name begins with "write-"
+    public static final String RESULTS_INDEX_WRITE_PREFIX = RESULTS_INDEX_PREFIX + ".write-";
     public static final String RESULTS_INDEX_DEFAULT = "shared";
 
     private AnomalyDetectorsIndexFields() {}

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/utils/MlIndexAndAlias.java

@@ -30,6 +30,8 @@
 import org.elasticsearch.core.Nullable;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.index.Index;
+import org.elasticsearch.index.IndexVersion;
+import org.elasticsearch.index.IndexVersions;
 import org.elasticsearch.indices.SystemIndexDescriptor;
 import org.elasticsearch.xcontent.XContentParserConfiguration;
 import org.elasticsearch.xcontent.json.JsonXContent;
@@ -63,27 +65,24 @@ public final class MlIndexAndAlias {
      */
     public static final String BWC_MAPPINGS_VERSION = "8.11.0";
 
-    private static final Logger logger = LogManager.getLogger(MlIndexAndAlias.class);
+    public static final String FIRST_INDEX_SIX_DIGIT_SUFFIX = "-000001";
 
-    static final Comparator<String> INDEX_NAME_COMPARATOR = new Comparator<>() {
-
-        private final Predicate<String> HAS_SIX_DIGIT_SUFFIX = Pattern.compile("\\d{6}").asMatchPredicate();
-
-        @Override
-        public int compare(String index1, String index2) {
-            String[] index1Parts = index1.split("-");
-            String index1Suffix = index1Parts[index1Parts.length - 1];
-            boolean index1HasSixDigitsSuffix = HAS_SIX_DIGIT_SUFFIX.test(index1Suffix);
-            String[] index2Parts = index2.split("-");
-            String index2Suffix = index2Parts[index2Parts.length - 1];
-            boolean index2HasSixDigitsSuffix = HAS_SIX_DIGIT_SUFFIX.test(index2Suffix);
-            if (index1HasSixDigitsSuffix && index2HasSixDigitsSuffix) {
-                return index1Suffix.compareTo(index2Suffix);
-            } else if (index1HasSixDigitsSuffix != index2HasSixDigitsSuffix) {
-                return Boolean.compare(index1HasSixDigitsSuffix, index2HasSixDigitsSuffix);
-            } else {
-                return index1.compareTo(index2);
-            }
+    private static final Logger logger = LogManager.getLogger(MlIndexAndAlias.class);
+    private static final Predicate<String> HAS_SIX_DIGIT_SUFFIX = Pattern.compile("\\d{6}").asMatchPredicate();
+
+    static final Comparator<String> INDEX_NAME_COMPARATOR = (index1, index2) -> {
+        String[] index1Parts = index1.split("-");
+        String index1Suffix = index1Parts[index1Parts.length - 1];
+        boolean index1HasSixDigitsSuffix = HAS_SIX_DIGIT_SUFFIX.test(index1Suffix);
+        String[] index2Parts = index2.split("-");
+        String index2Suffix = index2Parts[index2Parts.length - 1];
+        boolean index2HasSixDigitsSuffix = HAS_SIX_DIGIT_SUFFIX.test(index2Suffix);
+        if (index1HasSixDigitsSuffix && index2HasSixDigitsSuffix) {
+            return index1Suffix.compareTo(index2Suffix);
+        } else if (index1HasSixDigitsSuffix != index2HasSixDigitsSuffix) {
+            return Boolean.compare(index1HasSixDigitsSuffix, index2HasSixDigitsSuffix);
+        } else {
+            return index1.compareTo(index2);
         }
     };
 
@@ -124,7 +123,7 @@ public static void createIndexAndAliasIfNecessary(
         String legacyIndexWithoutSuffix = indexPatternPrefix;
         String indexPattern = indexPatternPrefix + "*";
         // The initial index name must be suitable for rollover functionality.
-        String firstConcreteIndex = indexPatternPrefix + "-000001";
+        String firstConcreteIndex = indexPatternPrefix + FIRST_INDEX_SIX_DIGIT_SUFFIX;
         String[] concreteIndexNames = resolver.concreteIndexNames(clusterState, IndicesOptions.lenientExpandHidden(), indexPattern);
         Optional<String> indexPointedByCurrentWriteAlias = clusterState.getMetadata().hasAlias(alias)
             ? clusterState.getMetadata().getIndicesLookup().get(alias).getIndices().stream().map(Index::getName).findFirst()
@@ -379,6 +378,10 @@ public static boolean hasIndexTemplate(ClusterState state, String templateName)
         return state.getMetadata().templatesV2().containsKey(templateName);
     }
 
+    public static boolean has6DigitSuffix(String indexName) {
+        return HAS_SIX_DIGIT_SUFFIX.test(indexName);
+    }
+
     /**
      * Returns the latest index. Latest is the index with the highest
      * 6 digit suffix.
@@ -390,4 +393,11 @@ public static String latestIndex(String[] concreteIndices) {
             ? concreteIndices[0]
             : Arrays.stream(concreteIndices).max(MlIndexAndAlias.INDEX_NAME_COMPARATOR).get();
     }
+
+    /**
+     * True if the version is read *and* write compatible not just read only compatible
+     */
+    public static boolean indexIsReadWriteCompatibleInV9(IndexVersion version) {
+        return version.onOrAfter(IndexVersions.V_8_0_0);
+    }
 }

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/ml/utils/MlIndexAndAliasTests.java

@@ -33,6 +33,7 @@
 import org.elasticsearch.common.util.concurrent.ThreadContext;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.index.IndexVersion;
+import org.elasticsearch.index.IndexVersions;
 import org.elasticsearch.indices.TestIndexNameExpressionResolver;
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.threadpool.ThreadPool;
@@ -364,8 +365,20 @@ public void testIndexNameComparator() {
     }
 
     public void testLatestIndex() {
-        var names = new String[] { "index-000001", "index-000002", "index-000003" };
-        assertThat(MlIndexAndAlias.latestIndex(names), equalTo("index-000003"));
+        {
+            var names = new String[] { "index-000001", "index-000002", "index-000003" };
+            assertThat(MlIndexAndAlias.latestIndex(names), equalTo("index-000003"));
+        }
+        {
+            var names = new String[] { "index", "index-000001", "index-000002" };
+            assertThat(MlIndexAndAlias.latestIndex(names), equalTo("index-000002"));
+        }
+    }
+
+    public void testIndexIsReadWriteCompatibleInV9() {
+        assertTrue(MlIndexAndAlias.indexIsReadWriteCompatibleInV9(IndexVersion.current()));
+        assertTrue(MlIndexAndAlias.indexIsReadWriteCompatibleInV9(IndexVersions.V_8_0_0));
+        assertFalse(MlIndexAndAlias.indexIsReadWriteCompatibleInV9(IndexVersions.V_7_17_0));
     }
 
     private void createIndexAndAliasIfNecessary(ClusterState clusterState) {

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/MachineLearning.java

@@ -1239,7 +1239,8 @@ public Collection<?> createComponents(PluginServices services) {
                     ),
                     indexNameExpressionResolver,
                     client
-                )
+                ),
+                new MlAnomaliesIndexUpdate(indexNameExpressionResolver, client)
             )
         );
         clusterService.addListener(mlAutoUpdateService);