Upgrade API: fix excessive logging and unnecessary template updates (#26698)

TemplateUpgradeService might get stuck in repeatedly upgrading templates after upgrade to 5.6.0. This is caused by shuffling mappings definition in the template during template serialization. This commit makes the template serialization consistent.

Closes #26673

Author: imotov

core/src/main/java/org/elasticsearch/cluster/metadata/IndexTemplateMetaData.java

@@ -26,7 +26,6 @@
 import org.elasticsearch.cluster.Diff;
 import org.elasticsearch.common.Nullable;
 import org.elasticsearch.common.bytes.BytesArray;
-import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.collect.ImmutableOpenMap;
 import org.elasticsearch.common.collect.MapBuilder;
 import org.elasticsearch.common.compress.CompressedXContent;
@@ -399,7 +398,7 @@ public static void toInnerXContent(IndexTemplateMetaData indexTemplateMetaData,
                 builder.startObject("mappings");
                 for (ObjectObjectCursor<String, CompressedXContent> cursor : indexTemplateMetaData.mappings()) {
                     byte[] mappingSource = cursor.value.uncompressed();
-                    Map<String, Object> mapping = XContentHelper.convertToMap(new BytesArray(mappingSource), false).v2();
+                    Map<String, Object> mapping = XContentHelper.convertToMap(new BytesArray(mappingSource), true).v2();
                     if (mapping.size() == 1 && mapping.containsKey(cursor.key)) {
                         // the type name is the root value, reduce it
                         mapping = (Map<String, Object>) mapping.get(cursor.key);

core/src/main/java/org/elasticsearch/cluster/metadata/TemplateUpgradeService.java

@@ -123,11 +123,11 @@ public void clusterChanged(ClusterChangedEvent event) {
         lastTemplateMetaData = templates;
         Optional<Tuple<Map<String, BytesReference>, Set<String>>> changes = calculateTemplateChanges(templates);
         if (changes.isPresent()) {
-            logger.info("Starting template upgrade to version {}, {} templates will be updated and {} will be removed",
-                Version.CURRENT,
-                changes.get().v1().size(),
-                changes.get().v2().size());
             if (updatesInProgress.compareAndSet(0, changes.get().v1().size() + changes.get().v2().size())) {
+                logger.info("Starting template upgrade to version {}, {} templates will be updated and {} will be removed",
+                    Version.CURRENT,
+                    changes.get().v1().size(),
+                    changes.get().v2().size());
                 threadPool.generic().execute(() -> updateTemplates(changes.get().v1(), changes.get().v2()));
             }
         }

core/src/test/java/org/elasticsearch/cluster/metadata/IndexTemplateMetaDataTests.java

@@ -0,0 +1,69 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.elasticsearch.cluster.metadata;
+
+import org.elasticsearch.common.bytes.BytesArray;
+import org.elasticsearch.common.bytes.BytesReference;
+import org.elasticsearch.common.xcontent.NamedXContentRegistry;
+import org.elasticsearch.common.xcontent.ToXContent;
+import org.elasticsearch.common.xcontent.XContentBuilder;
+import org.elasticsearch.common.xcontent.XContentHelper;
+import org.elasticsearch.common.xcontent.XContentParser;
+import org.elasticsearch.common.xcontent.XContentType;
+import org.elasticsearch.common.xcontent.json.JsonXContent;
+import org.elasticsearch.test.ESTestCase;
+
+import static java.util.Collections.singletonMap;
+import static org.hamcrest.CoreMatchers.equalTo;
+
+public class IndexTemplateMetaDataTests extends ESTestCase {
+
+    public void testIndexTemplateMetaDataXContentRoundTrip() throws Exception {
+        ToXContent.Params params = new ToXContent.MapParams(singletonMap("reduce_mappings", "true"));
+
+        String template = "{\"template\" : [ \".test-*\" ],\"order\" : 1000," +
+            "\"settings\" : {\"number_of_shards\" : 1,\"number_of_replicas\" : 0}," +
+            "\"mappings\" : {\"doc\" :" +
+            "{\"properties\":{\"" +
+            randomAlphaOfLength(10) + "\":{\"type\":\"text\"},\"" +
+            randomAlphaOfLength(10) + "\":{\"type\":\"keyword\"}}" +
+            "}}}";
+
+        BytesReference templateBytes = new BytesArray(template);
+        final IndexTemplateMetaData indexTemplateMetaData;
+        try (XContentParser parser = XContentHelper.createParser(NamedXContentRegistry.EMPTY, templateBytes, XContentType.JSON)) {
+            indexTemplateMetaData = IndexTemplateMetaData.Builder.fromXContent(parser, "test");
+        }
+
+        final BytesReference templateBytesRoundTrip;
+        try (XContentBuilder builder = XContentBuilder.builder(JsonXContent.jsonXContent)) {
+            builder.startObject();
+            IndexTemplateMetaData.Builder.toXContent(indexTemplateMetaData, builder, params);
+            builder.endObject();
+            templateBytesRoundTrip = builder.bytes();
+        }
+
+        final IndexTemplateMetaData indexTemplateMetaDataRoundTrip;
+        try (XContentParser parser = XContentHelper.createParser(NamedXContentRegistry.EMPTY, templateBytesRoundTrip, XContentType.JSON)) {
+            indexTemplateMetaDataRoundTrip = IndexTemplateMetaData.Builder.fromXContent(parser, "test");
+        }
+        assertThat(indexTemplateMetaData, equalTo(indexTemplateMetaDataRoundTrip));
+    }
+
+}