Add coordinating_only node selector (#30313)

Today we can execute cluster API actions on only master, data or ingest nodes using the `master:true`, `data:true` and `ingest:true` filters, but it is not so easy to select coordinating-only nodes (i.e. those nodes that are neither master nor data nor ingest nodes). This change fixes this by adding support for a `coordinating_only` filter such that `coordinating_only:true` adds all coordinating-only nodes to the set of selected nodes, and `coordinating_only:false` deletes them. Resolves #28831.

Author: PnPie

docs/CHANGELOG.asciidoc

@@ -333,6 +333,9 @@ started or stopped. ({pull}30118[#30118])
 
 Added put index template API to the high level rest client ({pull}30400[#30400])
 
+Add ability to filter coordinating-only nodes when interacting with cluster
+APIs. ({pull}30313[#30313])
+
 [float]
 === Bug Fixes
 

server/src/main/java/org/elasticsearch/cluster/node/DiscoveryNode.java

@@ -44,6 +44,8 @@
  */
 public class DiscoveryNode implements Writeable, ToXContentFragment {
 
+ static final String COORDINATING_ONLY = "coordinating_only";
+
  public static boolean nodeRequiresLocalStorage(Settings settings) {
  boolean localStorageEnable = Node.NODE_LOCAL_STORAGE_SETTING.get(settings);
  if (localStorageEnable == false &&

server/src/main/java/org/elasticsearch/cluster/node/DiscoveryNodes.java

@@ -147,6 +147,19 @@ public ImmutableOpenMap<String, DiscoveryNode> getMasterAndDataNodes() {
  return nodes.build();
  }
 
+ /**
+ * Get a {@link Map} of the coordinating only nodes (nodes which are neither master, nor data, nor ingest nodes) arranged by their ids
+ *
+ * @return {@link Map} of the coordinating only nodes arranged by their ids
+ */
+ public ImmutableOpenMap<String, DiscoveryNode> getCoordinatingOnlyNodes() {
+ ImmutableOpenMap.Builder<String, DiscoveryNode> nodes = ImmutableOpenMap.builder(this.nodes);
+ nodes.removeAll(masterNodes.keys());
+ nodes.removeAll(dataNodes.keys());
+ nodes.removeAll(ingestNodes.keys());
+ return nodes.build();
+ }
+
  /**
  * Get a node by its id
  *
@@ -294,7 +307,7 @@ public DiscoveryNode resolveNode(String node) {
  * - "_local" or "_master" for the relevant nodes
  * - a node id
  * - a wild card pattern that will be matched against node names
- * - a "attr:value" pattern, where attr can be a node role (master, data, ingest etc.) in which case the value can be true of false
+ * - a "attr:value" pattern, where attr can be a node role (master, data, ingest etc.) in which case the value can be true or false,
  * or a generic node attribute name in which case value will be treated as a wildcard and matched against the node attribute values.
  */
  public String[] resolveNodes(String... nodes) {
@@ -346,6 +359,12 @@ public String[] resolveNodes(String... nodes) {
  } else {
  resolvedNodesIds.removeAll(ingestNodes.keys());
  }
+ } else if (DiscoveryNode.COORDINATING_ONLY.equals(matchAttrName)) {
+ if (Booleans.parseBoolean(matchAttrValue, true)) {
+ resolvedNodesIds.addAll(getCoordinatingOnlyNodes().keys());
+ } else {
+ resolvedNodesIds.removeAll(getCoordinatingOnlyNodes().keys());
+ }
  } else {
  for (DiscoveryNode node : this) {
  for (Map.Entry<String, String> entry : node.getAttributes().entrySet()) {

server/src/test/java/org/elasticsearch/cluster/node/DiscoveryNodesTests.java

@@ -101,9 +101,17 @@ public void testCoordinatorOnlyNodes() {
  .map(DiscoveryNode::getId)
  .toArray(String[]::new);
 
- assertThat(
- discoveryNodes.resolveNodes("_all", "data:false", "ingest:false", "master:false"),
- arrayContainingInAnyOrder(coordinatorOnlyNodes));
+ final String[] nonCoordinatorOnlyNodes =
+ StreamSupport.stream(discoveryNodes.getNodes().values().spliterator(), false)
+ .map(n -> n.value)
+ .filter(n -> n.isMasterNode() || n.isDataNode() || n.isIngestNode())
+ .map(DiscoveryNode::getId)
+ .toArray(String[]::new);
+
+ assertThat(discoveryNodes.resolveNodes("coordinating_only:true"), arrayContainingInAnyOrder(coordinatorOnlyNodes));
+ assertThat(discoveryNodes.resolveNodes("_all", "data:false", "ingest:false", "master:false"),
+ arrayContainingInAnyOrder(coordinatorOnlyNodes));
+ assertThat(discoveryNodes.resolveNodes("_all", "coordinating_only:false"), arrayContainingInAnyOrder(nonCoordinatorOnlyNodes));
  }
 
  public void testResolveNodesIds() {
@@ -266,6 +274,13 @@ Set<String> matchingNodeIds(DiscoveryNodes nodes) {
  nodes.getIngestNodes().keysIt().forEachRemaining(ids::add);
  return ids;
  }
+ }, COORDINATING_ONLY(DiscoveryNode.COORDINATING_ONLY + ":true") {
+ @Override
+ Set<String> matchingNodeIds(DiscoveryNodes nodes) {
+ Set<String> ids = new HashSet<>();
+ nodes.getCoordinatingOnlyNodes().keysIt().forEachRemaining(ids::add);
+ return ids;
+ }
  }, CUSTOM_ATTRIBUTE("attr:value") {
  @Override
  Set<String> matchingNodeIds(DiscoveryNodes nodes) {