Add node "roles" to allocation explain response

docs/changelog/98550.yaml

@@ -0,0 +1,5 @@
+pr: 98550
+summary: Report a node's "roles" setting in the /_cluster/allocation/explain response
+area: Allocation
+type: enhancement
+issues: []

docs/reference/tab-widgets/troubleshooting/data/diagnose-unassigned-shards.asciidoc

@@ -20,12 +20,12 @@ In order to diagnose the unassigned shards, follow the next steps:
 . Log in to the {ess-console}[{ecloud} console].
 +
 
-. On the **Elasticsearch Service** panel, click the name of your deployment. 
+. On the **Elasticsearch Service** panel, click the name of your deployment.
 +
 
 NOTE: If the name of your deployment is disabled your {kib} instances might be
 unhealthy, in which case please contact https://support.elastic.co[Elastic Support].
-If your deployment doesn't include {kib}, all you need to do is 
+If your deployment doesn't include {kib}, all you need to do is
 {cloud}/ec-access-kibana.html[enable it first].
 
 . Open your deployment's side navigation menu (placed under the Elastic logo in the upper left corner)
@@ -106,6 +106,7 @@ The response will look like this:
       "node_id" : "8qt2rY-pT6KNZB3-hGfLnw",
       "node_name" : "node-0",
       "transport_address" : "127.0.0.1:9401",
+      "roles": [data, data_cold, data_content, data_frozen, data_hot, data_warm, ingest, master, ml, remote_cluster_client, transform]
       "node_attributes" : {},
       "node_decision" : "no",                     <4>
       "weight_ranking" : 1,
@@ -151,7 +152,7 @@ settings>> and <<cluster-update-settings,cluster update settings>> APIs to the
 correct values in order to allow the index to be allocated.
 
 For more guidance on fixing the most common causes for unassinged shards please follow
-<<fix-red-yellow-cluster-status, this guide>> or contact https://support.elastic.co[Elastic Support]. 
+<<fix-red-yellow-cluster-status, this guide>> or contact https://support.elastic.co[Elastic Support].
 
 //end::kibana-api-ex[]
 // end::cloud[]
@@ -231,6 +232,7 @@ The response will look like this:
       "node_id" : "8qt2rY-pT6KNZB3-hGfLnw",
       "node_name" : "node-0",
       "transport_address" : "127.0.0.1:9401",
+      "roles": [data, data_cold, data_content, data_frozen, data_hot, data_warm, ingest, master, ml, remote_cluster_client, transform]
       "node_attributes" : {},
       "node_decision" : "no",                     <4>
       "weight_ranking" : 1,
@@ -276,7 +278,7 @@ settings>> and <<cluster-update-settings,cluster update settings>> APIs to the
 correct values in order to allow the index to be allocated.
 
 For more guidance on fixing the most common causes for unassinged shards please follow
-<<fix-red-yellow-cluster-status, this guide>>. 
+<<fix-red-yellow-cluster-status, this guide>>.
 
 // end::self-managed[]
 

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/cluster.allocation_explain/10_basic.yml

@@ -92,3 +92,21 @@
   - is_true: can_rebalance_cluster
   - is_true: can_rebalance_to_other_node
   - is_true: rebalance_explanation
+
+---
+"Cluster allocation explanation response includes node's roles":
+  - skip:
+      version: " - 8.10.99"
+      reason: The roles field was introduced in 8.11.0
+
+  - do:
+      indices.create:
+        index: test
+
+  - match: { acknowledged: true }
+
+  - do:
+      cluster.allocation_explain:
+        body: { "index": "test", "shard": 0, "primary": true }
+
+  - is_true: current_node.roles

server/src/internalClusterTest/java/org/elasticsearch/action/admin/cluster/allocation/ClusterAllocationExplainIT.java

@@ -15,6 +15,7 @@
 import org.elasticsearch.cluster.health.ClusterHealthStatus;
 import org.elasticsearch.cluster.metadata.IndexMetadata;
 import org.elasticsearch.cluster.node.DiscoveryNode;
+import org.elasticsearch.cluster.node.DiscoveryNodeRole;
 import org.elasticsearch.cluster.routing.ShardRoutingState;
 import org.elasticsearch.cluster.routing.UnassignedInfo;
 import org.elasticsearch.cluster.routing.UnassignedInfo.AllocationStatus;
@@ -1150,6 +1151,42 @@ public void testCannotAllocateStaleReplicaExplanation() throws Exception {
         }
     }
 
+    public void testExplainRolesOutput() throws Exception {
+        logger.info("--> starting 1 node with 'roles' setting specified");
+        Settings roleSettings = Settings.builder().putList("node.roles", List.of("master", "data_hot", "ingest")).build();
+        internalCluster().startNode(Settings.builder().put(roleSettings).build());
+        prepareIndex(1, 0);
+
+        boolean includeYesDecisions = randomBoolean();
+        boolean includeDiskInfo = randomBoolean();
+        ClusterAllocationExplanation explanation = runExplain(true, includeYesDecisions, includeDiskInfo);
+
+        assertEquals(
+            Set.of(DiscoveryNodeRole.DATA_HOT_NODE_ROLE, DiscoveryNodeRole.INGEST_ROLE, DiscoveryNodeRole.MASTER_ROLE),
+            explanation.getCurrentNode().getRoles()
+        );
+
+        try (XContentParser parser = getParser(explanation)) {
+            // Fast-forward to the "current_node" object, which contains "roles".
+            do {
+                parser.nextToken();
+                assertNotEquals(Token.END_OBJECT, parser.currentToken());
+                // The START_OBJECT has a null currentName(), so check for that before de-referencing.
+            } while (parser.currentName() == null || (parser.currentName().equals("current_node")) == false);
+            assertEquals(Token.START_OBJECT, parser.nextToken());
+
+            // Fast-forward to "roles" field in the "current_node" object.
+            do {
+                parser.nextToken();
+                assertNotEquals(Token.END_OBJECT, parser.currentToken());
+            } while ((parser.currentName().equals("roles")) == false);
+
+            // Check that the "roles" reported are those explicitly set via the node Settings.
+            // Note: list() implicitly consumes the parser START_ARRAY and END_ARRAY tokens.
+            assertEquals(List.of("data_hot", "ingest", "master"), parser.list());
+        }
+    }
+
     private void verifyClusterInfo(ClusterInfo clusterInfo, boolean includeDiskInfo, int numNodes) {
         if (includeDiskInfo) {
             assertThat(clusterInfo.getNodeMostAvailableDiskUsages().size(), greaterThanOrEqualTo(0));
@@ -1309,8 +1346,11 @@ private void verifyShardInfo(XContentParser parser, boolean primary, boolean inc
                         parser.currentName().equals("id")
                             || parser.currentName().equals("name")
                             || parser.currentName().equals("transport_address")
+                            || parser.currentName().equals("roles")
                             || parser.currentName().equals("weight_ranking")
                     );
+                } else if (token == Token.START_ARRAY || token == Token.END_ARRAY) {
+                    assertEquals("roles", parser.currentName());
                 } else {
                     assertTrue(token.isValue());
                     assertNotNull(parser.text());
@@ -1436,6 +1476,10 @@ private String verifyNodeDecisionPrologue(XContentParser parser) throws IOExcept
         parser.nextToken();
         assertNotNull(parser.text());
         parser.nextToken();
+        assertEquals("roles", parser.currentName());
+        parser.nextToken();
+        assertNotEquals(0, parser.list().size());
+        parser.nextToken();
         assertEquals("node_decision", parser.currentName());
         parser.nextToken();
         return nodeName;

server/src/main/java/org/elasticsearch/cluster/routing/allocation/AbstractAllocationDecision.java

@@ -9,6 +9,7 @@
 package org.elasticsearch.cluster.routing.allocation;
 
 import org.elasticsearch.cluster.node.DiscoveryNode;
+import org.elasticsearch.cluster.node.DiscoveryNodeRole;
 import org.elasticsearch.cluster.routing.allocation.decider.Decision.Type;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
@@ -110,6 +111,11 @@ public static XContentBuilder discoveryNodeToXContent(DiscoveryNode node, boolea
             }
             builder.endObject();
         }
+        builder.startArray("roles");
+        for (DiscoveryNodeRole role : node.getRoles()) {
+            builder.value(role.roleName());
+        }
+        builder.endArray();
         return builder;
     }
 

server/src/test/java/org/elasticsearch/action/admin/cluster/allocation/ClusterAllocationExplainActionTests.java

@@ -35,6 +35,7 @@
 import java.time.Instant;
 import java.util.Collections;
 import java.util.Locale;
+import java.util.stream.Collectors;
 
 import static org.elasticsearch.action.admin.cluster.allocation.TransportClusterAllocationExplainAction.findShardToExplain;
 import static org.hamcrest.Matchers.allOf;
@@ -109,6 +110,7 @@ public ShardAllocationDecision decideShardAllocation(ShardRouting shard, Routing
             cae.getCurrentNode().getId(),
             cae.getCurrentNode().getName(),
             cae.getCurrentNode().getAddress(),
+            cae.getCurrentNode().getRoles().stream().map(r -> '"' + r.roleName() + '"').collect(Collectors.joining(", ", "[", "]")),
             explanation };
         assertEquals(XContentHelper.stripWhitespace(Strings.format("""
             {
@@ -120,7 +122,8 @@ public ShardAllocationDecision decideShardAllocation(ShardRouting shard, Routing
               "current_node": {
                 "id": "%s",
                 "name": "%s",
-                "transport_address": "%s"
+                "transport_address": "%s",
+                "roles": %s
               },
               "explanation": "%s"
             }""", args)), Strings.toString(builder));

server/src/test/java/org/elasticsearch/action/admin/cluster/allocation/ClusterAllocationExplanationTests.java

@@ -93,6 +93,7 @@ public void testExplanationToXContent() throws Exception {
                 "id": "node-0",
                 "name": "",
                 "transport_address": "%s",
+                "roles": [],
                 "weight_ranking": 3
               },
               "can_remain_on_current_node": "yes",
@@ -123,6 +124,7 @@ public void testRandomShardExplanationToXContent() throws Exception {
                                 "id": "node-0",
                                 "name": "",
                                 "transport_address": "%s",
+                                "roles": [],
                                 "weight_ranking": 3
                               },
                               "can_remain_on_current_node": "yes",