Add user-defined cluster metadata (elastic#33325)

Adds a place for users to store cluster-wide data they wish to associate with the cluster via the Cluster Settings API. This is strictly for user-defined data, Elasticsearch makes no other other use of these settings.

Author: gwbrown

docs/reference/modules/cluster/misc.asciidoc

@@ -22,6 +22,27 @@ user with access to the <<cluster-update-settings,cluster-update-settings>>
 API can make the cluster read-write again.
 
 
+[[user-defined-data]]
+==== User Defined Cluster Metadata
+
+User-defined metadata can be stored and retrieved using the Cluster Settings API.
+This can be used to store arbitrary, infrequently-changing data about the cluster
+without the need to create an index to store it. This data may be stored using
+any key prefixed with `cluster.metadata.`. For example, to store the email
+address of the administrator of a cluster under the key `cluster.metadata.administrator`,
+issue this request:
+
+[source,js]
+-------------------------------
+PUT /_cluster/settings
+{
+ "persistent": {
+ "cluster.metadata.administrator": "sysadmin@example.com"
+ }
+}
+-------------------------------
+// CONSOLE
+
 [[cluster-max-tombstones]]
 ==== Index Tombstones
 

server/src/main/java/org/elasticsearch/cluster/service/ClusterService.java

@@ -52,6 +52,9 @@ public class ClusterService extends AbstractLifecycleComponent {
  Setting.positiveTimeSetting("cluster.service.slow_task_logging_threshold", TimeValue.timeValueSeconds(30),
  Property.Dynamic, Property.NodeScope);
 
+ public static final org.elasticsearch.common.settings.Setting.AffixSetting<String> USER_DEFINED_META_DATA =
+ Setting.prefixKeySetting("cluster.metadata.", (key) -> Setting.simpleString(key, Property.Dynamic, Property.NodeScope));
+
  private final ClusterName clusterName;
 
  private final OperationRouting operationRouting;
@@ -68,6 +71,8 @@ public ClusterService(Settings settings, ClusterSettings clusterSettings, Thread
  this.clusterName = ClusterName.CLUSTER_NAME_SETTING.get(settings);
  this.clusterSettings.addSettingsUpdateConsumer(CLUSTER_SERVICE_SLOW_TASK_LOGGING_THRESHOLD_SETTING,
  this::setSlowTaskLoggingThreshold);
+ // Add a no-op update consumer so changes are logged
+ this.clusterSettings.addAffixUpdateConsumer(USER_DEFINED_META_DATA, (first, second) -> {}, (first, second) -> {});
  this.initialClusterStateCustoms = initialClusterStateCustoms;
  this.clusterApplierService = new ClusterApplierService(settings, clusterSettings, threadPool, this::newClusterStateBuilder);
  }

server/src/main/java/org/elasticsearch/common/settings/ClusterSettings.java

@@ -269,6 +269,7 @@ public void apply(Settings value, Settings current, Settings previous) {
  HierarchyCircuitBreakerService.ACCOUNTING_CIRCUIT_BREAKER_OVERHEAD_SETTING,
  IndexModule.NODE_STORE_ALLOW_MMAPFS,
  ClusterService.CLUSTER_SERVICE_SLOW_TASK_LOGGING_THRESHOLD_SETTING,
+ ClusterService.USER_DEFINED_META_DATA,
  SearchService.DEFAULT_SEARCH_TIMEOUT_SETTING,
  SearchService.DEFAULT_ALLOW_PARTIAL_SEARCH_RESULTS,
  ElectMasterService.DISCOVERY_ZEN_MINIMUM_MASTER_NODES_SETTING,

server/src/test/java/org/elasticsearch/cluster/settings/ClusterSettingsIT.java

@@ -22,6 +22,7 @@
 import org.apache.logging.log4j.Level;
 import org.elasticsearch.action.admin.cluster.settings.ClusterUpdateSettingsRequestBuilder;
 import org.elasticsearch.action.admin.cluster.settings.ClusterUpdateSettingsResponse;
+import org.elasticsearch.action.admin.cluster.state.ClusterStateResponse;
 import org.elasticsearch.cluster.metadata.MetaData;
 import org.elasticsearch.cluster.routing.allocation.decider.EnableAllocationDecider;
 import org.elasticsearch.common.logging.ESLoggerFactory;
@@ -380,4 +381,34 @@ public void testLoggerLevelUpdate() {
  }
  }
 
+ public void testUserMetadata() {
+ String key = "cluster.metadata." + randomAlphaOfLengthBetween(5, 20);
+ String value = randomRealisticUnicodeOfCodepointLengthBetween(5, 50);
+ String updatedValue = randomRealisticUnicodeOfCodepointLengthBetween(5, 50);
+ logger.info("Attempting to store [{}]: [{}], then update to [{}]", key, value, updatedValue);
+
+ final Settings settings = Settings.builder().put(key, value).build();
+ final Settings updatedSettings = Settings.builder().put(key, updatedValue).build();
+ if (randomBoolean()) {
+ logger.info("Using persistent settings");
+
+ client().admin().cluster().prepareUpdateSettings().setPersistentSettings(settings).execute().actionGet();
+ ClusterStateResponse state = client().admin().cluster().prepareState().execute().actionGet();
+ assertEquals(value, state.getState().getMetaData().persistentSettings().get(key));
+
+ client().admin().cluster().prepareUpdateSettings().setPersistentSettings(updatedSettings).execute().actionGet();
+ ClusterStateResponse updatedState = client().admin().cluster().prepareState().execute().actionGet();
+ assertEquals(updatedValue, updatedState.getState().getMetaData().persistentSettings().get(key));
+ } else {
+ logger.info("Using transient settings");
+ client().admin().cluster().prepareUpdateSettings().setTransientSettings(settings).execute().actionGet();
+ ClusterStateResponse state = client().admin().cluster().prepareState().execute().actionGet();
+ assertEquals(value, state.getState().getMetaData().transientSettings().get(key));
+
+ client().admin().cluster().prepareUpdateSettings().setTransientSettings(updatedSettings).execute().actionGet();
+ ClusterStateResponse updatedState = client().admin().cluster().prepareState().execute().actionGet();
+ assertEquals(updatedValue, updatedState.getState().getMetaData().transientSettings().get(key));
+ }
+ }
+
 }