Add a new node role 'cluster_manager' as the alternative for 'master' role and deprecate 'master' role (#2424)

Add a new node role `cluster_manager`, as the replacement for `master` role, that used in setting `node.roles: [ master ]`. 
They have got the same functionality, but can NOT be assigned to `node.roles` together.
* Add `CLUSTER_MANAGER_ROLE` in `DiscoveryNodeRole` class, and deprecate `MASTER_ROLE`
* Remove `MASTER_ROLE` from the `DiscoveryNodeRole.BUILT_IN_ROLES`, and temporarily load the role by the existing method `DiscoveryNode.setAdditionalRoles`
* Add a method `validateRole()` in `DiscoveryNodeRole` class, it's used to validate a specific role is compatible with the other roles to be assigned to a node together.
* Add deprecation message when assigning `master` role in setting `node.roles`
* Replace most `MASTER_ROLE` with `CLUSTER_MANAGER_ROLE` in current unit and integration tests
* Add new unit and integration tests to validate `CLUSTER_MANAGER_ROLE` and `MASTER_ROLE` can be treated as the same.

More explanation:
* New node will have "cluster_manager", "data", and "ingest" roles by default. Which means the default value of setting "node.roles" will be `["cluster_manager","data","ingest"]`, instead of `["master","data","ingest"]`
* "cluster_manager" role will be treated as "master" role in the OpenSearch node of previous versions.
* "cluster_manager” role and "master" role have got the same abbreviation name: "m"

Signed-off-by: Tianli Feng <ftianli@amazon.com>

benchmarks/src/main/java/org/opensearch/benchmark/routing/allocation/Allocators.java

@@ -111,7 +111,7 @@ public final class Allocators {
             nodeId,
             new TransportAddress(TransportAddress.META_ADDRESS, portGenerator.incrementAndGet()),
             attributes,
-            Sets.newHashSet(DiscoveryNodeRole.MASTER_ROLE, DiscoveryNodeRole.DATA_ROLE),
+            Sets.newHashSet(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE, DiscoveryNodeRole.DATA_ROLE),
             Version.CURRENT
         );
     }

client/rest/src/main/java/org/opensearch/client/Node.java

@@ -210,21 +210,21 @@ public class Node {
         }
 
         /**
-         * Teturns whether or not the node <strong>could</strong> be elected master.
+         * Returns whether or not the node <strong>could</strong> be elected master.
          */
         public boolean isMasterEligible() {
-            return roles.contains("master");
+            return roles.contains("master") || roles.contains("cluster_manager");
         }
 
         /**
-         * Teturns whether or not the node stores data.
+         * Returns whether or not the node stores data.
          */
         public boolean isData() {
             return roles.contains("data");
         }
 
         /**
-         * Teturns whether or not the node runs ingest pipelines.
+         * Returns whether or not the node runs ingest pipelines.
          */
         public boolean isIngest() {
             return roles.contains("ingest");

rest-api-spec/src/main/resources/rest-api-spec/test/cluster.stats/10_basic.yml

@@ -91,3 +91,22 @@
       cluster.stats: {}
 
   - is_true: nodes.packaging_types
+
+---
+"get cluster stats nodes count with both master and cluster_manager":
+  - skip:
+      version: " - 1.4.99"
+      reason: "node role cluster_manager is added in 2.0.0"
+
+  - do:
+      cluster.stats: {}
+
+  - set:
+      nodes.count.cluster_manager: cluster_manager_count
+
+  - gte: { nodes.count.total: 1}
+  - match: { nodes.count.cluster_manager: $cluster_manager_count }
+  - match: { nodes.count.master: $cluster_manager_count }
+  - gte: { nodes.count.data: 1}
+  - gte: { nodes.count.ingest: 0}
+  - gte: { nodes.count.coordinating_only: 0}

rest-api-spec/src/main/resources/rest-api-spec/test/nodes.info/10_basic.yml

@@ -12,14 +12,24 @@ setup:
   - is_true: cluster_name
 
 ---
-"node_info role test":
+"node_info role test - before 2.0.0":
   - skip:
-      version: " - 7.7.99"
+      version: " - 7.7.99 , 2.0.0 - "
       reason: "node roles were not sorted before 7.8.0"
+      features: node_selector
 
   - do:
       nodes.info: {}
+      node_selector:
+        # Only send request to nodes in <2.0 versions, especially during ':qa:mixed-cluster:v1.x.x#mixedClusterTest'.
+        # Because YAML REST test takes the minimum OpenSearch version in the cluster to apply the filter in 'skip' section,
+        # see OpenSearchClientYamlSuiteTestCase#initAndResetContext() for detail.
+        # During 'mixedClusterTest', the cluster can be mixed with nodes in 1.x and 2.x versions,
+        # so node_selector is required, and only filtering version in 'skip' is not enough.
+        version: "1.0.0 - 1.4.99"
+
   - set:
+      # Note: It will only stash the first node_id in the api response.
       nodes._arbitrary_key_: node_id
 
   - is_true: nodes.$node_id.roles
@@ -29,3 +39,21 @@ setup:
   - match: { nodes.$node_id.roles.2: "master" }
   - match: { nodes.$node_id.roles.3: "remote_cluster_client" }
 
+---
+"node_info role test":
+  - skip:
+      version: " - 1.4.99"
+      reason: "node role cluster_manager is added in 2.0.0"
+
+  - do:
+      nodes.info: {}
+
+  - set:
+      nodes._arbitrary_key_: node_id
+
+  - is_true: nodes.$node_id.roles
+  # the roles output is sorted
+  - match: { nodes.$node_id.roles.0: "cluster_manager" }
+  - match: { nodes.$node_id.roles.1: "data" }
+  - match: { nodes.$node_id.roles.2: "ingest" }
+  - match: { nodes.$node_id.roles.3: "remote_cluster_client" }

server/src/internalClusterTest/java/org/opensearch/action/admin/cluster/stats/ClusterStatsIT.java

@@ -85,6 +85,7 @@ public class ClusterStatsIT extends OpenSearchIntegTestCase {
         Map<String, Integer> expectedCounts = new HashMap<>();
         expectedCounts.put(DiscoveryNodeRole.DATA_ROLE.roleName(), 1);
         expectedCounts.put(DiscoveryNodeRole.MASTER_ROLE.roleName(), 1);
+        expectedCounts.put(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE.roleName(), 1);
         expectedCounts.put(DiscoveryNodeRole.INGEST_ROLE.roleName(), 1);
         expectedCounts.put(DiscoveryNodeRole.REMOTE_CLUSTER_CLIENT_ROLE.roleName(), 1);
         expectedCounts.put(ClusterStatsNodes.Counts.COORDINATING_ONLY, 0);
@@ -106,7 +107,7 @@ public class ClusterStatsIT extends OpenSearchIntegTestCase {
                 roles.add(DiscoveryNodeRole.INGEST_ROLE);
             }
             if (isMasterNode) {
-                roles.add(DiscoveryNodeRole.MASTER_ROLE);
+                roles.add(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE);
             }
             if (isRemoteClusterClientNode) {
                 roles.add(DiscoveryNodeRole.REMOTE_CLUSTER_CLIENT_ROLE);
@@ -129,6 +130,7 @@ public class ClusterStatsIT extends OpenSearchIntegTestCase {
             }
             if (isMasterNode) {
                 incrementCountForRole(DiscoveryNodeRole.MASTER_ROLE.roleName(), expectedCounts);
+                incrementCountForRole(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE.roleName(), expectedCounts);
             }
             if (isRemoteClusterClientNode) {
                 incrementCountForRole(DiscoveryNodeRole.REMOTE_CLUSTER_CLIENT_ROLE.roleName(), expectedCounts);

server/src/internalClusterTest/java/org/opensearch/env/NodeEnvironmentIT.java

@@ -95,7 +95,7 @@ public class NodeEnvironmentIT extends OpenSearchIntegTestCase {
             })
         );
         if (writeDanglingIndices) {
-            assertThat(ex.getMessage(), startsWith("node does not have the data and master roles but has index metadata"));
+            assertThat(ex.getMessage(), startsWith("node does not have the data and cluster_manager roles but has index metadata"));
         } else {
             assertThat(ex.getMessage(), startsWith("node does not have the data role but has shard data"));
         }

server/src/main/java/org/opensearch/action/admin/cluster/stats/ClusterStatsNodes.java

@@ -223,7 +223,14 @@ public class ClusterStatsNodes implements ToXContentFragment {
                     roles.merge(COORDINATING_ONLY, 1, Integer::sum);
                 } else {
                     for (DiscoveryNodeRole role : nodeInfo.getNode().getRoles()) {
-                        roles.merge(role.roleName(), 1, Integer::sum);
+                        // TODO: Remove the 'if' condition and only keep the statement in 'else' after removing MASTER_ROLE.
+                        // As of 2.0, CLUSTER_MANAGER_ROLE is added, and it should be taken as MASTER_ROLE
+                        if (role.isClusterManager()) {
+                            roles.merge(DiscoveryNodeRole.MASTER_ROLE.roleName(), 1, Integer::sum);
+                            roles.merge(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE.roleName(), 1, Integer::sum);
+                        } else {
+                            roles.merge(role.roleName(), 1, Integer::sum);
+                        }
                     }
                 }
             }

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

@@ -94,7 +94,7 @@ public class DiscoveryNode implements Writeable, ToXContentFragment {
     }
 
     public static boolean isMasterNode(Settings settings) {
-        return hasRole(settings, DiscoveryNodeRole.MASTER_ROLE);
+        return hasRole(settings, DiscoveryNodeRole.MASTER_ROLE) || hasRole(settings, DiscoveryNodeRole.CLUSTER_MANAGER_ROLE);
     }
 
     /**
@@ -343,7 +343,7 @@ public class DiscoveryNode implements Writeable, ToXContentFragment {
                 final LegacyRole legacyRole = in.readEnum(LegacyRole.class);
                 switch (legacyRole) {
                     case MASTER:
-                        roles.add(DiscoveryNodeRole.MASTER_ROLE);
+                        roles.add(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE);
                         break;
                     case DATA:
                         roles.add(DiscoveryNodeRole.DATA_ROLE);
@@ -390,11 +390,11 @@ public class DiscoveryNode implements Writeable, ToXContentFragment {
                 .collect(Collectors.toList());
             out.writeVInt(rolesToWrite.size());
             for (final DiscoveryNodeRole role : rolesToWrite) {
-                if (role == DiscoveryNodeRole.MASTER_ROLE) {
+                if (role.isClusterManager()) {
                     out.writeEnum(LegacyRole.MASTER);
-                } else if (role == DiscoveryNodeRole.DATA_ROLE) {
+                } else if (role.equals(DiscoveryNodeRole.DATA_ROLE)) {
                     out.writeEnum(LegacyRole.DATA);
-                } else if (role == DiscoveryNodeRole.INGEST_ROLE) {
+                } else if (role.equals(DiscoveryNodeRole.INGEST_ROLE)) {
                     out.writeEnum(LegacyRole.INGEST);
                 }
             }
@@ -456,7 +456,7 @@ public class DiscoveryNode implements Writeable, ToXContentFragment {
      * Can this node become master or not.
      */
     public boolean isMasterNode() {
-        return roles.contains(DiscoveryNodeRole.MASTER_ROLE);
+        return roles.contains(DiscoveryNodeRole.MASTER_ROLE) || roles.contains(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE);
     }
 
     /**
@@ -591,7 +591,11 @@ public class DiscoveryNode implements Writeable, ToXContentFragment {
             + "], roles by name abbreviation ["
             + roleNameAbbreviationToPossibleRoles
             + "]";
-        roleMap = roleNameToPossibleRoles;
+        // TODO: Remove the Map 'roleNameToPossibleRolesWithMaster' and let 'roleMap = roleNameToPossibleRoles', after removing MASTER_ROLE.
+        // It's used to allow CLUSTER_MANAGER_ROLE that introduced in 2.0, having the same abbreviation name with MASTER_ROLE.
+        final Map<String, DiscoveryNodeRole> roleNameToPossibleRolesWithMaster = new HashMap<>(roleNameToPossibleRoles);
+        roleNameToPossibleRolesWithMaster.put(DiscoveryNodeRole.MASTER_ROLE.roleName(), DiscoveryNodeRole.MASTER_ROLE);
+        roleMap = Collections.unmodifiableMap(roleNameToPossibleRolesWithMaster);
     }
 
     public static Set<String> getPossibleRoleNames() {
@@ -599,7 +603,7 @@ public class DiscoveryNode implements Writeable, ToXContentFragment {
     }
 
     /**
-     * Enum that holds all the possible roles that that a node can fulfill in a cluster.
+     * Enum that holds all the possible roles that a node can fulfill in a cluster.
      * Each role has its name and a corresponding abbreviation used by cat apis.
      */
     private enum LegacyRole {

server/src/main/java/org/opensearch/cluster/node/DiscoveryNodeRole.java

@@ -34,6 +34,7 @@ package org.opensearch.cluster.node;
 
 import org.opensearch.LegacyESVersion;
 import org.opensearch.Version;
+import org.opensearch.common.logging.DeprecationLogger;
 import org.opensearch.common.settings.Setting;
 import org.opensearch.common.settings.Setting.Property;
 import org.opensearch.common.settings.Settings;
@@ -41,6 +42,8 @@ import org.opensearch.transport.RemoteClusterService;
 
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.List;
+import java.util.Locale;
 import java.util.Objects;
 import java.util.SortedSet;
 import java.util.TreeSet;
@@ -50,6 +53,10 @@ import java.util.TreeSet;
  */
 public abstract class DiscoveryNodeRole implements Comparable<DiscoveryNodeRole> {
 
+    private static final DeprecationLogger deprecationLogger = DeprecationLogger.getLogger(DiscoveryNodeRole.class);
+    public static final String MASTER_ROLE_DEPRECATION_MESSAGE =
+        "Assigning [master] role in setting [node.roles] is deprecated. To promote inclusive language, please use [cluster_manager] role instead.";
+
     private final String roleName;
 
     /**
@@ -129,6 +136,13 @@ public abstract class DiscoveryNodeRole implements Comparable<DiscoveryNodeRole>
         return this;
     }
 
+    /**
+     * Validate the role is compatible with the other roles in the list, when assigning the list of roles to a node.
+     * An {@link IllegalArgumentException} is expected to be thrown, if the role can't coexist with the other roles.
+     * @param roles a {@link List} of {@link DiscoveryNodeRole} that a node is going to have
+     */
+    public void validateRole(List<DiscoveryNodeRole> roles) {};
+
     @Override
     public final boolean equals(Object o) {
         if (this == o) return true;
@@ -193,15 +207,60 @@ public abstract class DiscoveryNodeRole implements Comparable<DiscoveryNodeRole>
 
     /**
      * Represents the role for a master-eligible node.
+     * @deprecated As of 2.0, because promoting inclusive language, replaced by {@link #CLUSTER_MANAGER_ROLE}
      */
+    @Deprecated
     public static final DiscoveryNodeRole MASTER_ROLE = new DiscoveryNodeRole("master", "m") {
 
+        @Override
+        public Setting<Boolean> legacySetting() {
+            // copy the setting here so we can mark it private in org.opensearch.node.Node
+            // As of 2.0, set the default value to 'false', so that MASTER_ROLE isn't added as a default value of NODE_ROLES_SETTING
+            return Setting.boolSetting("node.master", false, Property.Deprecated, Property.NodeScope);
+        }
+
+        @Override
+        public void validateRole(List<DiscoveryNodeRole> roles) {
+            deprecationLogger.deprecate("node_role_master", MASTER_ROLE_DEPRECATION_MESSAGE);
+        }
+
+    };
+
+    /**
+     * Represents the role for a cluster-manager-eligible node.
+     */
+    public static final DiscoveryNodeRole CLUSTER_MANAGER_ROLE = new DiscoveryNodeRole("cluster_manager", "m") {
+
         @Override
         public Setting<Boolean> legacySetting() {
             // copy the setting here so we can mark it private in org.opensearch.node.Node
             return Setting.boolSetting("node.master", true, Property.Deprecated, Property.NodeScope);
         }
 
+        @Override
+        public DiscoveryNodeRole getCompatibilityRole(Version nodeVersion) {
+            if (nodeVersion.onOrAfter(Version.V_2_0_0)) {
+                return this;
+            } else {
+                return DiscoveryNodeRole.MASTER_ROLE;
+            }
+        }
+
+        @Override
+        public void validateRole(List<DiscoveryNodeRole> roles) {
+            if (roles.contains(DiscoveryNodeRole.MASTER_ROLE)) {
+                throw new IllegalArgumentException(
+                    String.format(
+                        Locale.ROOT,
+                        "The two roles [%s, %s] can not be assigned together to a node. %s",
+                        DiscoveryNodeRole.MASTER_ROLE.roleName(),
+                        DiscoveryNodeRole.CLUSTER_MANAGER_ROLE.roleName(),
+                        MASTER_ROLE_DEPRECATION_MESSAGE
+                    )
+                );
+            }
+        }
+
     };
 
     public static final DiscoveryNodeRole REMOTE_CLUSTER_CLIENT_ROLE = new DiscoveryNodeRole("remote_cluster_client", "r") {
@@ -223,7 +282,7 @@ public abstract class DiscoveryNodeRole implements Comparable<DiscoveryNodeRole>
      * The built-in node roles.
      */
     public static SortedSet<DiscoveryNodeRole> BUILT_IN_ROLES = Collections.unmodifiableSortedSet(
-        new TreeSet<>(Arrays.asList(DATA_ROLE, INGEST_ROLE, MASTER_ROLE, REMOTE_CLUSTER_CLIENT_ROLE))
+        new TreeSet<>(Arrays.asList(DATA_ROLE, INGEST_ROLE, CLUSTER_MANAGER_ROLE, REMOTE_CLUSTER_CLIENT_ROLE))
     );
 
     /**
@@ -262,4 +321,13 @@ public abstract class DiscoveryNodeRole implements Comparable<DiscoveryNodeRole>
 
     }
 
+    /**
+     * Check if the role is {@link #CLUSTER_MANAGER_ROLE} or {@link #MASTER_ROLE}.
+     * @deprecated As of 2.0, because promoting inclusive language. MASTER_ROLE is deprecated.
+     * @return true if the node role is{@link #CLUSTER_MANAGER_ROLE} or {@link #MASTER_ROLE}
+     */
+    @Deprecated
+    public boolean isClusterManager() {
+        return this.equals(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE) || this.equals(DiscoveryNodeRole.MASTER_ROLE);
+    }
 }

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

@@ -370,7 +370,7 @@ public class DiscoveryNodes extends AbstractDiffable<DiscoveryNodes> implements
      * Works by tracking the current set of nodes and applying each node specification in sequence. The set starts out empty and each node
      * specification may either add or remove nodes. For instance:
      *
-     * - _local, _master and _all respectively add to the subset the local node, the currently-elected master, and all the nodes
+     * - _local, _cluster_manager (_master) and _all respectively add to the subset the local node, the currently-elected cluster_manager, and all the nodes
      * - node IDs, names, hostnames and IP addresses all add to the subset any nodes which match
      * - a wildcard-based pattern of the form "attr*:value*" adds to the subset all nodes with a matching attribute with a matching value
      * - role:true adds to the subset all nodes with a matching role
@@ -393,7 +393,7 @@ public class DiscoveryNodes extends AbstractDiffable<DiscoveryNodes> implements
                     if (localNodeId != null) {
                         resolvedNodesIds.add(localNodeId);
                     }
-                } else if (nodeId.equals("_master")) {
+                } else if (nodeId.equals("_master") || nodeId.equals("_cluster_manager")) {
                     String masterNodeId = getMasterNodeId();
                     if (masterNodeId != null) {
                         resolvedNodesIds.add(masterNodeId);
@@ -419,7 +419,7 @@ public class DiscoveryNodes extends AbstractDiffable<DiscoveryNodes> implements
                             } else {
                                 resolvedNodesIds.removeAll(dataNodes.keys());
                             }
-                        } else if (DiscoveryNodeRole.MASTER_ROLE.roleName().equals(matchAttrName)) {
+                        } else if (roleNameIsClusterManager(matchAttrName)) {
                             if (Booleans.parseBoolean(matchAttrValue, true)) {
                                 resolvedNodesIds.addAll(masterNodes.keys());
                             } else {
@@ -797,4 +797,17 @@ public class DiscoveryNodes extends AbstractDiffable<DiscoveryNodes> implements
             return masterNodeId != null && masterNodeId.equals(localNodeId);
         }
     }
+
+    /**
+     * Check if the given name of the node role is 'cluster_manger' or 'master'.
+     * The method is added for {@link #resolveNodes} to keep the code clear, when support the both above roles.
+     * @deprecated As of 2.0, because promoting inclusive language. MASTER_ROLE is deprecated.
+     * @param matchAttrName a given String for a name of the node role.
+     * @return true if the given roleName is 'cluster_manger' or 'master'
+     */
+    @Deprecated
+    private boolean roleNameIsClusterManager(String matchAttrName) {
+        return DiscoveryNodeRole.MASTER_ROLE.roleName().equals(matchAttrName)
+            || DiscoveryNodeRole.CLUSTER_MANAGER_ROLE.roleName().equals(matchAttrName);
+    }
 }

server/src/main/java/org/opensearch/env/NodeEnvironment.java

@@ -1138,7 +1138,7 @@ public final class NodeEnvironment implements Closeable {
                 Locale.ROOT,
                 "node does not have the %s and %s roles but has index metadata: %s. Use 'opensearch-node repurpose' tool to clean up",
                 DiscoveryNodeRole.DATA_ROLE.roleName(),
-                DiscoveryNodeRole.MASTER_ROLE.roleName(),
+                DiscoveryNodeRole.CLUSTER_MANAGER_ROLE.roleName(),
                 indexMetadataPaths
             );
             throw new IllegalStateException(message);

server/src/main/java/org/opensearch/node/NodeRoleSettings.java

@@ -51,7 +51,11 @@ public class NodeRoleSettings {
             .filter(role -> role.isEnabledByDefault(settings))
             .map(DiscoveryNodeRole::roleName)
             .collect(Collectors.toList()),
-        roles -> {},
+        roles -> {
+            for (DiscoveryNodeRole role : roles) {
+                role.validateRole(roles);
+            }
+        },
         Property.NodeScope
     );
 

server/src/main/java/org/opensearch/repositories/RepositoriesService.java

@@ -346,8 +346,9 @@ public class RepositoriesService extends AbstractLifecycleComponent implements C
         });
     }
 
+    // Note: "voting_only" role has not been implemented yet, so the method always returns false.
     static boolean isDedicatedVotingOnlyNode(Set<DiscoveryNodeRole> roles) {
-        return roles.contains(DiscoveryNodeRole.MASTER_ROLE)
+        return roles.contains(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE)
             && roles.contains(DiscoveryNodeRole.DATA_ROLE) == false
             && roles.stream().anyMatch(role -> role.roleName().equals("voting_only"));
     }

server/src/test/java/org/opensearch/action/admin/cluster/configuration/AddVotingConfigExclusionsRequestTests.java

@@ -113,7 +113,7 @@ public class AddVotingConfigExclusionsRequestTests extends OpenSearchTestCase {
             "local",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            singleton(DiscoveryNodeRole.MASTER_ROLE),
+            singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         final VotingConfigExclusion localNodeExclusion = new VotingConfigExclusion(localNode);
@@ -122,7 +122,7 @@ public class AddVotingConfigExclusionsRequestTests extends OpenSearchTestCase {
             "other1",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            singleton(DiscoveryNodeRole.MASTER_ROLE),
+            singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         final VotingConfigExclusion otherNode1Exclusion = new VotingConfigExclusion(otherNode1);
@@ -131,7 +131,7 @@ public class AddVotingConfigExclusionsRequestTests extends OpenSearchTestCase {
             "other2",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            singleton(DiscoveryNodeRole.MASTER_ROLE),
+            singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         final VotingConfigExclusion otherNode2Exclusion = new VotingConfigExclusion(otherNode2);
@@ -238,7 +238,7 @@ public class AddVotingConfigExclusionsRequestTests extends OpenSearchTestCase {
             "nodeId1",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            singleton(DiscoveryNodeRole.MASTER_ROLE),
+            singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         final VotingConfigExclusion node1Exclusion = new VotingConfigExclusion(node1);
@@ -248,7 +248,7 @@ public class AddVotingConfigExclusionsRequestTests extends OpenSearchTestCase {
             "nodeId2",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            singleton(DiscoveryNodeRole.MASTER_ROLE),
+            singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         final VotingConfigExclusion node2Exclusion = new VotingConfigExclusion(node2);
@@ -258,7 +258,7 @@ public class AddVotingConfigExclusionsRequestTests extends OpenSearchTestCase {
             "nodeId3",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            singleton(DiscoveryNodeRole.MASTER_ROLE),
+            singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
 
@@ -298,7 +298,7 @@ public class AddVotingConfigExclusionsRequestTests extends OpenSearchTestCase {
             "nodeId1",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            singleton(DiscoveryNodeRole.MASTER_ROLE),
+            singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         final VotingConfigExclusion node1Exclusion = new VotingConfigExclusion(node1);
@@ -308,7 +308,7 @@ public class AddVotingConfigExclusionsRequestTests extends OpenSearchTestCase {
             "nodeId2",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            singleton(DiscoveryNodeRole.MASTER_ROLE),
+            singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         final VotingConfigExclusion node2Exclusion = new VotingConfigExclusion(node2);
@@ -318,7 +318,7 @@ public class AddVotingConfigExclusionsRequestTests extends OpenSearchTestCase {
             "nodeId3",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            singleton(DiscoveryNodeRole.MASTER_ROLE),
+            singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
 
@@ -348,7 +348,7 @@ public class AddVotingConfigExclusionsRequestTests extends OpenSearchTestCase {
             "nodeId1",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            singleton(DiscoveryNodeRole.MASTER_ROLE),
+            singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
 
@@ -357,7 +357,7 @@ public class AddVotingConfigExclusionsRequestTests extends OpenSearchTestCase {
             "nodeId2",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            singleton(DiscoveryNodeRole.MASTER_ROLE),
+            singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         final VotingConfigExclusion node2Exclusion = new VotingConfigExclusion(node2);
@@ -367,7 +367,7 @@ public class AddVotingConfigExclusionsRequestTests extends OpenSearchTestCase {
             "nodeId3",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            singleton(DiscoveryNodeRole.MASTER_ROLE),
+            singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
 
@@ -399,7 +399,7 @@ public class AddVotingConfigExclusionsRequestTests extends OpenSearchTestCase {
             "local",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            singleton(DiscoveryNodeRole.MASTER_ROLE),
+            singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         final VotingConfigExclusion localNodeExclusion = new VotingConfigExclusion(localNode);
@@ -408,7 +408,7 @@ public class AddVotingConfigExclusionsRequestTests extends OpenSearchTestCase {
             "other1",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            singleton(DiscoveryNodeRole.MASTER_ROLE),
+            singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         final VotingConfigExclusion otherNode1Exclusion = new VotingConfigExclusion(otherNode1);
@@ -417,7 +417,7 @@ public class AddVotingConfigExclusionsRequestTests extends OpenSearchTestCase {
             "other2",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            singleton(DiscoveryNodeRole.MASTER_ROLE),
+            singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         final VotingConfigExclusion otherNode2Exclusion = new VotingConfigExclusion(otherNode2);

server/src/test/java/org/opensearch/action/admin/cluster/configuration/TransportAddVotingConfigExclusionsActionTests.java

@@ -119,7 +119,7 @@ public class TransportAddVotingConfigExclusionsActionTests extends OpenSearchTes
             name,
             buildNewFakeTransportAddress(),
             emptyMap(),
-            singleton(DiscoveryNodeRole.MASTER_ROLE),
+            singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
     }

server/src/test/java/org/opensearch/action/admin/indices/shrink/TransportResizeActionTests.java

@@ -278,7 +278,7 @@ public class TransportResizeActionTests extends OpenSearchTestCase {
 
     private DiscoveryNode newNode(String nodeId) {
         final Set<DiscoveryNodeRole> roles = Collections.unmodifiableSet(
-            new HashSet<>(Arrays.asList(DiscoveryNodeRole.MASTER_ROLE, DiscoveryNodeRole.DATA_ROLE))
+            new HashSet<>(Arrays.asList(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE, DiscoveryNodeRole.DATA_ROLE))
         );
         return new DiscoveryNode(nodeId, buildNewFakeTransportAddress(), emptyMap(), roles, Version.CURRENT);
     }

server/src/test/java/org/opensearch/action/search/TransportMultiSearchActionTests.java

@@ -263,7 +263,7 @@ public class TransportMultiSearchActionTests extends OpenSearchTestCase {
                 "master",
                 buildNewFakeTransportAddress(),
                 Collections.emptyMap(),
-                Collections.singleton(DiscoveryNodeRole.MASTER_ROLE),
+                Collections.singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
                 Version.CURRENT
             )
         );

server/src/test/java/org/opensearch/action/support/master/TransportMasterNodeActionTests.java

@@ -121,14 +121,14 @@ public class TransportMasterNodeActionTests extends OpenSearchTestCase {
             "local_node",
             buildNewFakeTransportAddress(),
             Collections.emptyMap(),
-            Collections.singleton(DiscoveryNodeRole.MASTER_ROLE),
+            Collections.singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         remoteNode = new DiscoveryNode(
             "remote_node",
             buildNewFakeTransportAddress(),
             Collections.emptyMap(),
-            Collections.singleton(DiscoveryNodeRole.MASTER_ROLE),
+            Collections.singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         allNodes = new DiscoveryNode[] { localNode, remoteNode };

server/src/test/java/org/opensearch/action/support/nodes/TransportNodesActionTests.java

@@ -172,7 +172,9 @@ public class TransportNodesActionTests extends OpenSearchTestCase {
     private enum NodeSelector {
         LOCAL("_local"),
         ELECTED_MASTER("_master"),
+        // TODO: Remove this element after removing DiscoveryNodeRole.MASTER_ROLE
         MASTER_ELIGIBLE("master:true"),
+        CLUSTER_MANAGER_ELIGIBLE("cluster_manager:true"),
         DATA("data:true"),
         CUSTOM_ATTRIBUTE("attr:value");
 

server/src/test/java/org/opensearch/cluster/ClusterChangedEventTests.java

@@ -447,17 +447,17 @@ public class ClusterChangedEventTests extends OpenSearchTestCase {
             if (i == 0) {
                 // the master node
                 builder.masterNodeId(nodeId);
-                roles.add(DiscoveryNodeRole.MASTER_ROLE);
+                roles.add(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE);
             } else if (i == 1) {
                 // the alternate master node
-                roles.add(DiscoveryNodeRole.MASTER_ROLE);
+                roles.add(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE);
             } else if (i == 2) {
                 // we need at least one data node
                 roles.add(DiscoveryNodeRole.DATA_ROLE);
             } else {
                 // remaining nodes can be anything (except for master)
                 if (randomBoolean()) {
-                    roles.add(DiscoveryNodeRole.MASTER_ROLE);
+                    roles.add(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE);
                 }
                 if (randomBoolean()) {
                     roles.add(DiscoveryNodeRole.DATA_ROLE);

server/src/test/java/org/opensearch/cluster/coordination/ClusterBootstrapServiceTests.java

@@ -112,7 +112,7 @@ public class ClusterBootstrapServiceTests extends OpenSearchTestCase {
             randomAlphaOfLength(10),
             buildNewFakeTransportAddress(),
             emptyMap(),
-            Collections.singleton(DiscoveryNodeRole.MASTER_ROLE),
+            Collections.singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
     }
@@ -522,7 +522,7 @@ public class ClusterBootstrapServiceTests extends OpenSearchTestCase {
                     randomAlphaOfLength(10),
                     buildNewFakeTransportAddress(),
                     emptyMap(),
-                    Collections.singleton(DiscoveryNodeRole.MASTER_ROLE),
+                    Collections.singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
                     Version.CURRENT
                 ),
                 new DiscoveryNode(
@@ -530,7 +530,7 @@ public class ClusterBootstrapServiceTests extends OpenSearchTestCase {
                     randomAlphaOfLength(10),
                     otherNode1.getAddress(),
                     emptyMap(),
-                    Collections.singleton(DiscoveryNodeRole.MASTER_ROLE),
+                    Collections.singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
                     Version.CURRENT
                 )
             ).collect(Collectors.toList())

server/src/test/java/org/opensearch/cluster/coordination/ClusterFormationFailureHelperTests.java

@@ -287,7 +287,7 @@ public class ClusterFormationFailureHelperTests extends OpenSearchTestCase {
             "local",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            org.opensearch.common.collect.Set.of(DiscoveryNodeRole.MASTER_ROLE),
+            org.opensearch.common.collect.Set.of(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         clusterState = ClusterState.builder(ClusterName.DEFAULT)
@@ -825,7 +825,7 @@ public class ClusterFormationFailureHelperTests extends OpenSearchTestCase {
             emptyMap(),
             new HashSet<>(
                 randomSubsetOf(DiscoveryNodeRole.BUILT_IN_ROLES).stream()
-                    .filter(r -> r != DiscoveryNodeRole.MASTER_ROLE)
+                    .filter(r -> r != DiscoveryNodeRole.CLUSTER_MANAGER_ROLE)
                     .collect(Collectors.toList())
             ),
             Version.CURRENT

server/src/test/java/org/opensearch/cluster/coordination/CoordinatorTests.java

@@ -1789,7 +1789,7 @@ public class CoordinatorTests extends AbstractCoordinatorTestCase {
                     "resolvableNodeId",
                     buildNewFakeTransportAddress(),
                     emptyMap(),
-                    singleton(DiscoveryNodeRole.MASTER_ROLE),
+                    singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
                     Version.CURRENT
                 )
             )

server/src/test/java/org/opensearch/cluster/coordination/NodeJoinTests.java

@@ -248,7 +248,7 @@ public class NodeJoinTests extends OpenSearchTestCase {
     protected DiscoveryNode newNode(int i, boolean master) {
         final Set<DiscoveryNodeRole> roles;
         if (master) {
-            roles = singleton(DiscoveryNodeRole.MASTER_ROLE);
+            roles = singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE);
         } else {
             roles = Collections.emptySet();
         }
@@ -492,7 +492,7 @@ public class NodeJoinTests extends OpenSearchTestCase {
             "newNodeId",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            singleton(DiscoveryNodeRole.MASTER_ROLE),
+            singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         long newTerm = initialTerm + randomLongBetween(1, 10);

server/src/test/java/org/opensearch/cluster/health/ClusterHealthAllocationTests.java

@@ -87,7 +87,9 @@ public class ClusterHealthAllocationTests extends OpenSearchAllocationTestCase {
 
     private ClusterState addNode(ClusterState clusterState, String nodeName, boolean isMaster) {
         DiscoveryNodes.Builder nodeBuilder = DiscoveryNodes.builder(clusterState.getNodes());
-        nodeBuilder.add(newNode(nodeName, Collections.singleton(isMaster ? DiscoveryNodeRole.MASTER_ROLE : DiscoveryNodeRole.DATA_ROLE)));
+        nodeBuilder.add(
+            newNode(nodeName, Collections.singleton(isMaster ? DiscoveryNodeRole.CLUSTER_MANAGER_ROLE : DiscoveryNodeRole.DATA_ROLE))
+        );
         return ClusterState.builder(clusterState).nodes(nodeBuilder).build();
     }
 

server/src/test/java/org/opensearch/cluster/metadata/AutoExpandReplicasTests.java

@@ -146,7 +146,7 @@ public class AutoExpandReplicasTests extends OpenSearchTestCase {
 
         try {
             List<DiscoveryNode> allNodes = new ArrayList<>();
-            DiscoveryNode localNode = createNode(DiscoveryNodeRole.MASTER_ROLE); // local node is the master
+            DiscoveryNode localNode = createNode(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE); // local node is the master
             allNodes.add(localNode);
             int numDataNodes = randomIntBetween(3, 5);
             List<DiscoveryNode> dataNodes = new ArrayList<>(numDataNodes);
@@ -245,7 +245,7 @@ public class AutoExpandReplicasTests extends OpenSearchTestCase {
             List<DiscoveryNode> allNodes = new ArrayList<>();
             DiscoveryNode oldNode = createNode(
                 VersionUtils.randomVersionBetween(random(), LegacyESVersion.V_7_0_0, LegacyESVersion.V_7_5_1),
-                DiscoveryNodeRole.MASTER_ROLE,
+                DiscoveryNodeRole.CLUSTER_MANAGER_ROLE,
                 DiscoveryNodeRole.DATA_ROLE
             ); // local node is the master
             allNodes.add(oldNode);
@@ -266,11 +266,11 @@ public class AutoExpandReplicasTests extends OpenSearchTestCase {
                 state = cluster.reroute(state, new ClusterRerouteRequest());
             }
 
-            DiscoveryNode newNode = createNode(LegacyESVersion.V_7_6_0, DiscoveryNodeRole.MASTER_ROLE, DiscoveryNodeRole.DATA_ROLE); // local
+            DiscoveryNode newNode = createNode(
-                                                                                                                                     // node
+                LegacyESVersion.V_7_6_0,
-                                                                                                                                     // is
+                DiscoveryNodeRole.CLUSTER_MANAGER_ROLE,
-                                                                                                                                     // the
+                DiscoveryNodeRole.DATA_ROLE
-                                                                                                                                     // master
+            ); // local node is the cluster_manager
 
             state = cluster.addNodes(state, Collections.singletonList(newNode));
 

server/src/test/java/org/opensearch/cluster/metadata/MetadataCreateIndexServiceTests.java

@@ -582,7 +582,7 @@ public class MetadataCreateIndexServiceTests extends OpenSearchTestCase {
 
     private DiscoveryNode newNode(String nodeId) {
         final Set<DiscoveryNodeRole> roles = Collections.unmodifiableSet(
-            new HashSet<>(Arrays.asList(DiscoveryNodeRole.MASTER_ROLE, DiscoveryNodeRole.DATA_ROLE))
+            new HashSet<>(Arrays.asList(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE, DiscoveryNodeRole.DATA_ROLE))
         );
         return new DiscoveryNode(nodeId, buildNewFakeTransportAddress(), emptyMap(), roles, Version.CURRENT);
     }

server/src/test/java/org/opensearch/cluster/metadata/TemplateUpgradeServiceTests.java

@@ -261,7 +261,7 @@ public class TemplateUpgradeServiceTests extends OpenSearchTestCase {
     }
 
     private static final Set<DiscoveryNodeRole> MASTER_DATA_ROLES = Collections.unmodifiableSet(
-        new HashSet<>(Arrays.asList(DiscoveryNodeRole.MASTER_ROLE, DiscoveryNodeRole.DATA_ROLE))
+        new HashSet<>(Arrays.asList(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE, DiscoveryNodeRole.DATA_ROLE))
     );
 
     @SuppressWarnings("unchecked")

server/src/test/java/org/opensearch/cluster/node/DiscoveryNodeRoleSettingTests.java

@@ -56,9 +56,15 @@ public class DiscoveryNodeRoleSettingTests extends OpenSearchTestCase {
     }
 
     public void testIsMasterNode() {
+        // It's used to add MASTER_ROLE into 'roleMap', because MASTER_ROLE is removed from DiscoveryNodeRole.BUILT_IN_ROLES in 2.0.
+        DiscoveryNode.setAdditionalRoles(Collections.emptySet());
         runRoleTest(DiscoveryNode::isMasterNode, DiscoveryNodeRole.MASTER_ROLE);
     }
 
+    public void testIsClusterManagerNode() {
+        runRoleTest(DiscoveryNode::isMasterNode, DiscoveryNodeRole.CLUSTER_MANAGER_ROLE);
+    }
+
     public void testIsRemoteClusterClient() {
         runRoleTest(DiscoveryNode::isRemoteClusterClient, DiscoveryNodeRole.REMOTE_CLUSTER_CLIENT_ROLE);
     }

server/src/test/java/org/opensearch/cluster/node/DiscoveryNodeRoleTests.java

@@ -128,4 +128,14 @@ public class DiscoveryNodeRoleTests extends OpenSearchTestCase {
             assertNotEquals(buildInRole.toString(), unknownDataRole.toString());
         }
     }
+
+    /**
+     * Validate the method can identify the role as cluster-manager.
+     * Remove along with MASTER_ROLE.
+     */
+    public void testIsClusterManager() {
+        assertTrue(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE.isClusterManager());
+        assertTrue(DiscoveryNodeRole.MASTER_ROLE.isClusterManager());
+        assertFalse(randomFrom(DiscoveryNodeRole.DATA_ROLE.isClusterManager(), DiscoveryNodeRole.INGEST_ROLE.isClusterManager()));
+    }
 }

server/src/test/java/org/opensearch/cluster/node/DiscoveryNodeTests.java

@@ -174,6 +174,12 @@ public class DiscoveryNodeTests extends OpenSearchTestCase {
         runTestDiscoveryNodeIsRemoteClusterClient(nonRemoteClusterClientNode(), false);
     }
 
+    // TODO: Remove the test along with MASTER_ROLE. It is added in 2.0, along with the introduction of CLUSTER_MANAGER_ROLE.
+    public void testSetAdditionalRolesCanAddDeprecatedMasterRole() {
+        DiscoveryNode.setAdditionalRoles(Collections.emptySet());
+        assertTrue(DiscoveryNode.getPossibleRoleNames().contains(DiscoveryNodeRole.MASTER_ROLE.roleName()));
+    }
+
     private void runTestDiscoveryNodeIsRemoteClusterClient(final Settings settings, final boolean expected) {
         final DiscoveryNode node = DiscoveryNode.createLocal(settings, new TransportAddress(TransportAddress.META_ADDRESS, 9200), "node");
         assertThat(node.isRemoteClusterClient(), equalTo(expected));

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

@@ -361,6 +361,7 @@ public class DiscoveryNodesTests extends OpenSearchTestCase {
                 return Collections.singleton(nodes.getMasterNodeId());
             }
         },
+        // TODO: Remove this element after removing DiscoveryNodeRole.MASTER_ROLE
         MASTER_ELIGIBLE(DiscoveryNodeRole.MASTER_ROLE.roleName() + ":true") {
             @Override
             Set<String> matchingNodeIds(DiscoveryNodes nodes) {
@@ -369,6 +370,14 @@ public class DiscoveryNodesTests extends OpenSearchTestCase {
                 return ids;
             }
         },
+        CLUSTER_MANAGER_ELIGIBLE(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE.roleName() + ":true") {
+            @Override
+            Set<String> matchingNodeIds(DiscoveryNodes nodes) {
+                Set<String> ids = new HashSet<>();
+                nodes.getMasterNodes().keysIt().forEachRemaining(ids::add);
+                return ids;
+            }
+        },
         DATA(DiscoveryNodeRole.DATA_ROLE.roleName() + ":true") {
             @Override
             Set<String> matchingNodeIds(DiscoveryNodes nodes) {

server/src/test/java/org/opensearch/cluster/routing/DelayedAllocationServiceTests.java

@@ -262,7 +262,7 @@ public class DelayedAllocationServiceTests extends OpenSearchAllocationTestCase
             .routingTable(RoutingTable.builder().addAsNew(metadata.index("short_delay")).addAsNew(metadata.index("long_delay")).build())
             .nodes(
                 DiscoveryNodes.builder()
-                    .add(newNode("node0", singleton(DiscoveryNodeRole.MASTER_ROLE)))
+                    .add(newNode("node0", singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE)))
                     .localNodeId("node0")
                     .masterNodeId("node0")
                     .add(newNode("node1"))

server/src/test/java/org/opensearch/cluster/routing/OperationRoutingTests.java

@@ -778,7 +778,7 @@ public class OperationRoutingTests extends OpenSearchTestCase {
             "master",
             buildNewFakeTransportAddress(),
             Collections.emptyMap(),
-            Collections.singleton(DiscoveryNodeRole.MASTER_ROLE),
+            Collections.singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         allNodes[i] = master;

server/src/test/java/org/opensearch/cluster/routing/allocation/AllocationCommandsTests.java

@@ -188,7 +188,7 @@ public class AllocationCommandsTests extends OpenSearchAllocationTestCase {
                     .add(newNode("node1"))
                     .add(newNode("node2"))
                     .add(newNode("node3"))
-                    .add(newNode("node4", singleton(DiscoveryNodeRole.MASTER_ROLE)))
+                    .add(newNode("node4", singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE)))
             )
             .build();
         clusterState = allocation.reroute(clusterState, "reroute");
@@ -748,7 +748,9 @@ public class AllocationCommandsTests extends OpenSearchAllocationTestCase {
             "test2",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            new HashSet<>(randomSubsetOf(new HashSet<>(Arrays.asList(DiscoveryNodeRole.MASTER_ROLE, DiscoveryNodeRole.INGEST_ROLE)))),
+            new HashSet<>(
+                randomSubsetOf(new HashSet<>(Arrays.asList(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE, DiscoveryNodeRole.INGEST_ROLE)))
+            ),
             Version.CURRENT
         );
 
@@ -817,7 +819,9 @@ public class AllocationCommandsTests extends OpenSearchAllocationTestCase {
             "test2",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            new HashSet<>(randomSubsetOf(new HashSet<>(Arrays.asList(DiscoveryNodeRole.MASTER_ROLE, DiscoveryNodeRole.INGEST_ROLE)))),
+            new HashSet<>(
+                randomSubsetOf(new HashSet<>(Arrays.asList(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE, DiscoveryNodeRole.INGEST_ROLE)))
+            ),
             Version.CURRENT
         );
 

server/src/test/java/org/opensearch/cluster/routing/allocation/FailedNodeRoutingTests.java

@@ -230,7 +230,7 @@ public class FailedNodeRoutingTests extends OpenSearchAllocationTestCase {
 
     public ClusterState randomInitialClusterState() {
         List<DiscoveryNode> allNodes = new ArrayList<>();
-        DiscoveryNode localNode = createNode(DiscoveryNodeRole.MASTER_ROLE); // local node is the master
+        DiscoveryNode localNode = createNode(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE); // local node is the master
         allNodes.add(localNode);
         // at least two nodes that have the data role so that we can allocate shards
         allNodes.add(createNode(DiscoveryNodeRole.DATA_ROLE));

server/src/test/java/org/opensearch/cluster/routing/allocation/decider/DiskThresholdDeciderTests.java

@@ -1078,7 +1078,7 @@ public class DiskThresholdDeciderTests extends OpenSearchAllocationTestCase {
             "node1",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            singleton(DiscoveryNodeRole.MASTER_ROLE),
+            singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         DiscoveryNode discoveryNode2 = new DiscoveryNode(
@@ -1227,7 +1227,7 @@ public class DiskThresholdDeciderTests extends OpenSearchAllocationTestCase {
             "master",
             buildNewFakeTransportAddress(),
             emptyMap(),
-            singleton(DiscoveryNodeRole.MASTER_ROLE),
+            singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         DiscoveryNode dataNode = new DiscoveryNode(

server/src/test/java/org/opensearch/cluster/routing/allocation/decider/RestoreInProgressAllocationDeciderTests.java

@@ -199,7 +199,7 @@ public class RestoreInProgressAllocationDeciderTests extends OpenSearchAllocatio
         RoutingTable routingTable = RoutingTable.builder().addAsNew(metadata.index("test")).build();
 
         DiscoveryNodes discoveryNodes = DiscoveryNodes.builder()
-            .add(newNode("master", Collections.singleton(DiscoveryNodeRole.MASTER_ROLE)))
+            .add(newNode("master", Collections.singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE)))
             .localNodeId("master")
             .masterNodeId("master")
             .build();

server/src/test/java/org/opensearch/env/NodeEnvironmentTests.java

@@ -602,7 +602,7 @@ public class NodeEnvironmentTests extends OpenSearchTestCase {
         );
 
         assertThat(ex.getMessage(), containsString(indexPath.resolve(MetadataStateFormat.STATE_DIR_NAME).toAbsolutePath().toString()));
-        assertThat(ex.getMessage(), startsWith("node does not have the data and master roles but has index metadata"));
+        assertThat(ex.getMessage(), startsWith("node does not have the data and cluster_manager roles but has index metadata"));
     }
 
     /** Converts an array of Strings to an array of Paths, adding an additional child if specified */

server/src/test/java/org/opensearch/env/NodeRepurposeCommandTests.java

@@ -105,7 +105,7 @@ public class NodeRepurposeCommandTests extends OpenSearchTestCase {
         dataNoMasterSettings = nonMasterNode(dataMasterSettings);
         noDataNoMasterSettings = removeRoles(
             dataMasterSettings,
-            Collections.unmodifiableSet(new HashSet<>(Arrays.asList(DiscoveryNodeRole.DATA_ROLE, DiscoveryNodeRole.MASTER_ROLE)))
+            Collections.unmodifiableSet(new HashSet<>(Arrays.asList(DiscoveryNodeRole.DATA_ROLE, DiscoveryNodeRole.CLUSTER_MANAGER_ROLE)))
         );
 
         noDataMasterSettings = masterNode(nonDataNode(dataMasterSettings));

server/src/test/java/org/opensearch/gateway/ClusterStateUpdatersTests.java

@@ -304,7 +304,7 @@ public class ClusterStateUpdatersTests extends OpenSearchTestCase {
             "node1",
             buildNewFakeTransportAddress(),
             Collections.emptyMap(),
-            Sets.newHashSet(DiscoveryNodeRole.MASTER_ROLE),
+            Sets.newHashSet(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
 
@@ -354,7 +354,7 @@ public class ClusterStateUpdatersTests extends OpenSearchTestCase {
             "node1",
             buildNewFakeTransportAddress(),
             Collections.emptyMap(),
-            Sets.newHashSet(DiscoveryNodeRole.MASTER_ROLE),
+            Sets.newHashSet(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         final ClusterState updatedState = Function.<ClusterState>identity()

server/src/test/java/org/opensearch/gateway/GatewayMetaStatePersistedStateTests.java

@@ -97,7 +97,7 @@ public class GatewayMetaStatePersistedStateTests extends OpenSearchTestCase {
             "node1",
             buildNewFakeTransportAddress(),
             Collections.emptyMap(),
-            Sets.newHashSet(DiscoveryNodeRole.MASTER_ROLE),
+            Sets.newHashSet(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE),
             Version.CURRENT
         );
         clusterName = new ClusterName(randomAlphaOfLength(10));

server/src/test/java/org/opensearch/indices/cluster/IndicesClusterStateServiceRandomUpdatesTests.java

@@ -327,7 +327,7 @@ public class IndicesClusterStateServiceRandomUpdatesTests extends AbstractIndice
         Supplier<MockIndicesService> indicesServiceSupplier
     ) {
         List<DiscoveryNode> allNodes = new ArrayList<>();
-        DiscoveryNode localNode = createNode(DiscoveryNodeRole.MASTER_ROLE); // local node is the master
+        DiscoveryNode localNode = createNode(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE); // local node is the master
         allNodes.add(localNode);
         // at least two nodes that have the data role so that we can allocate shards
         allNodes.add(createNode(DiscoveryNodeRole.DATA_ROLE));

server/src/test/java/org/opensearch/node/NodeRoleSettingsTests.java

@@ -0,0 +1,57 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.node;
+
+import org.opensearch.cluster.node.DiscoveryNode;
+import org.opensearch.cluster.node.DiscoveryNodeRole;
+import org.opensearch.common.settings.Settings;
+import org.opensearch.test.OpenSearchTestCase;
+
+import java.util.Arrays;
+import java.util.Collections;
+
+import static org.hamcrest.Matchers.containsString;
+
+public class NodeRoleSettingsTests extends OpenSearchTestCase {
+
+    /**
+     * Validate cluster_manager role and master role can not coexist in a node.
+     * Remove the test after removing MASTER_ROLE.
+     */
+    public void testClusterManagerAndMasterRoleCanNotCoexist() {
+        // It's used to add MASTER_ROLE into 'roleMap', because MASTER_ROLE is removed from DiscoveryNodeRole.BUILT_IN_ROLES in 2.0.
+        DiscoveryNode.setAdditionalRoles(Collections.emptySet());
+        Settings roleSettings = Settings.builder().put(NodeRoleSettings.NODE_ROLES_SETTING.getKey(), "cluster_manager, master").build();
+        Exception exception = expectThrows(IllegalArgumentException.class, () -> NodeRoleSettings.NODE_ROLES_SETTING.get(roleSettings));
+        assertThat(exception.getMessage(), containsString("[master, cluster_manager] can not be assigned together to a node"));
+    }
+
+    /**
+     * Validate cluster_manager role and data role can coexist in a node. The test is added along with validateRole().
+     */
+    public void testClusterManagerAndDataNodeRoles() {
+        Settings roleSettings = Settings.builder().put(NodeRoleSettings.NODE_ROLES_SETTING.getKey(), "cluster_manager, data").build();
+        assertEquals(
+            Arrays.asList(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE, DiscoveryNodeRole.DATA_ROLE),
+            NodeRoleSettings.NODE_ROLES_SETTING.get(roleSettings)
+        );
+    }
+
+    /**
+     * Validate setting master role will result a deprecation message.
+     * Remove the test after removing MASTER_ROLE.
+     */
+    public void testMasterRoleDeprecationMessage() {
+        // It's used to add MASTER_ROLE into 'roleMap', because MASTER_ROLE is removed from DiscoveryNodeRole.BUILT_IN_ROLES in 2.0.
+        DiscoveryNode.setAdditionalRoles(Collections.emptySet());
+        Settings roleSettings = Settings.builder().put(NodeRoleSettings.NODE_ROLES_SETTING.getKey(), "master").build();
+        assertEquals(Collections.singletonList(DiscoveryNodeRole.MASTER_ROLE), NodeRoleSettings.NODE_ROLES_SETTING.get(roleSettings));
+        assertWarnings(DiscoveryNodeRole.MASTER_ROLE_DEPRECATION_MESSAGE);
+    }
+}

server/src/test/java/org/opensearch/persistent/PersistentTasksClusterServiceTests.java

@@ -886,7 +886,7 @@ public class PersistentTasksClusterServiceTests extends OpenSearchTestCase {
 
     private DiscoveryNode newNode(String nodeId) {
         final Set<DiscoveryNodeRole> roles = Collections.unmodifiableSet(
-            new HashSet<>(Arrays.asList(DiscoveryNodeRole.MASTER_ROLE, DiscoveryNodeRole.DATA_ROLE))
+            new HashSet<>(Arrays.asList(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE, DiscoveryNodeRole.DATA_ROLE))
         );
         return new DiscoveryNode(nodeId, buildNewFakeTransportAddress(), emptyMap(), roles, Version.CURRENT);
     }

server/src/test/java/org/opensearch/snapshots/SnapshotResiliencyTests.java

@@ -1500,7 +1500,7 @@ public class SnapshotResiliencyTests extends OpenSearchTestCase {
         }
 
         private TestClusterNode newMasterNode(String nodeName) throws IOException {
-            return newNode(nodeName, DiscoveryNodeRole.MASTER_ROLE);
+            return newNode(nodeName, DiscoveryNodeRole.CLUSTER_MANAGER_ROLE);
         }
 
         private TestClusterNode newDataNode(String nodeName) throws IOException {

server/src/test/java/org/opensearch/transport/SniffConnectionStrategyTests.java

@@ -747,7 +747,7 @@ public class SniffConnectionStrategyTests extends OpenSearchTestCase {
                 "id",
                 address,
                 Collections.emptyMap(),
-                new HashSet<>(Arrays.asList(DiscoveryNodeRole.DATA_ROLE, DiscoveryNodeRole.MASTER_ROLE)),
+                new HashSet<>(Arrays.asList(DiscoveryNodeRole.DATA_ROLE, DiscoveryNodeRole.CLUSTER_MANAGER_ROLE)),
                 Version.CURRENT
             );
             assertTrue(nodePredicate.test(dataMaster));
@@ -757,7 +757,7 @@ public class SniffConnectionStrategyTests extends OpenSearchTestCase {
                 "id",
                 address,
                 Collections.emptyMap(),
-                new HashSet<>(Arrays.asList(DiscoveryNodeRole.MASTER_ROLE)),
+                new HashSet<>(Arrays.asList(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE)),
                 Version.CURRENT
             );
             assertFalse(nodePredicate.test(dedicatedMaster));
@@ -777,7 +777,7 @@ public class SniffConnectionStrategyTests extends OpenSearchTestCase {
                 "id",
                 address,
                 Collections.emptyMap(),
-                new HashSet<>(Arrays.asList(DiscoveryNodeRole.INGEST_ROLE, DiscoveryNodeRole.MASTER_ROLE)),
+                new HashSet<>(Arrays.asList(DiscoveryNodeRole.INGEST_ROLE, DiscoveryNodeRole.CLUSTER_MANAGER_ROLE)),
                 Version.CURRENT
             );
             assertTrue(nodePredicate.test(masterIngest));
@@ -855,7 +855,7 @@ public class SniffConnectionStrategyTests extends OpenSearchTestCase {
         TransportAddress address = new TransportAddress(TransportAddress.META_ADDRESS, 0);
         Settings settings = Settings.builder().put("cluster.remote.node.attr", "gateway").build();
         Predicate<DiscoveryNode> nodePredicate = SniffConnectionStrategy.getNodePredicate(settings);
-        Set<DiscoveryNodeRole> dedicatedMasterRoles = new HashSet<>(Arrays.asList(DiscoveryNodeRole.MASTER_ROLE));
+        Set<DiscoveryNodeRole> dedicatedMasterRoles = new HashSet<>(Arrays.asList(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE));
         Set<DiscoveryNodeRole> allRoles = DiscoveryNodeRole.BUILT_IN_ROLES;
         {
             DiscoveryNode node = new DiscoveryNode(

test/framework/src/main/java/org/opensearch/cluster/OpenSearchAllocationTestCase.java

@@ -149,7 +149,7 @@ public abstract class OpenSearchAllocationTestCase extends OpenSearchTestCase {
     }
 
     protected static Set<DiscoveryNodeRole> MASTER_DATA_ROLES = Collections.unmodifiableSet(
-        new HashSet<>(Arrays.asList(DiscoveryNodeRole.MASTER_ROLE, DiscoveryNodeRole.DATA_ROLE))
+        new HashSet<>(Arrays.asList(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE, DiscoveryNodeRole.DATA_ROLE))
     );
 
     protected static DiscoveryNode newNode(String nodeId) {

test/framework/src/main/java/org/opensearch/cluster/coordination/CoordinationStateTestCluster.java

@@ -164,10 +164,10 @@ public class CoordinationStateTestCluster {
 
             final Set<DiscoveryNodeRole> roles = new HashSet<>(localNode.getRoles());
             if (randomBoolean()) {
-                if (roles.contains(DiscoveryNodeRole.MASTER_ROLE)) {
+                if (roles.contains(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE)) {
-                    roles.remove(DiscoveryNodeRole.MASTER_ROLE);
+                    roles.remove(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE);
                 } else {
-                    roles.add(DiscoveryNodeRole.MASTER_ROLE);
+                    roles.add(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE);
                 }
             }
 

test/framework/src/main/java/org/opensearch/test/InternalTestCluster.java

@@ -787,13 +787,13 @@ public final class InternalTestCluster extends TestCluster {
         String suffix = "";
         // only add the suffixes if roles are explicitly defined
         if (settings.hasValue("nodes.roles")) {
-            if (DiscoveryNode.hasRole(settings, DiscoveryNodeRole.MASTER_ROLE)) {
+            if (DiscoveryNode.isMasterNode(settings)) {
-                suffix = suffix + DiscoveryNodeRole.MASTER_ROLE.roleNameAbbreviation();
+                suffix = suffix + DiscoveryNodeRole.CLUSTER_MANAGER_ROLE.roleNameAbbreviation();
             }
             if (DiscoveryNode.isDataNode(settings)) {
                 suffix = suffix + DiscoveryNodeRole.DATA_ROLE.roleNameAbbreviation();
             }
-            if (DiscoveryNode.hasRole(settings, DiscoveryNodeRole.MASTER_ROLE) == false && DiscoveryNode.isDataNode(settings) == false) {
+            if (!DiscoveryNode.isMasterNode(settings) && !DiscoveryNode.isDataNode(settings)) {
                 suffix = suffix + "c";
             }
         }
@@ -2150,7 +2150,7 @@ public final class InternalTestCluster extends TestCluster {
     }
 
     public List<String> startMasterOnlyNodes(int numNodes, Settings settings) {
-        return startNodes(numNodes, Settings.builder().put(onlyRole(settings, DiscoveryNodeRole.MASTER_ROLE)).build());
+        return startNodes(numNodes, Settings.builder().put(onlyRole(settings, DiscoveryNodeRole.CLUSTER_MANAGER_ROLE)).build());
     }
 
     public List<String> startDataOnlyNodes(int numNodes) {

test/framework/src/main/java/org/opensearch/test/NodeRoles.java

@@ -80,6 +80,13 @@ public class NodeRoles {
                 NodeRoleSettings.NODE_ROLES_SETTING.get(settings)
                     .stream()
                     .filter(r -> roles.contains(r) == false)
+                    // TODO: Remove the below filter after removing MASTER_ROLE.
+                    // It's used to remove both CLUSTER_MANAGER_ROLE and MASTER_ROLE, when requested to remove either.
+                    .filter(
+                        roles.contains(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE) || roles.contains(DiscoveryNodeRole.MASTER_ROLE)
+                            ? r -> !r.isClusterManager()
+                            : r -> true
+                    )
                     .map(DiscoveryNodeRole::roleName)
                     .collect(Collectors.toList())
             )
@@ -166,7 +173,7 @@ public class NodeRoles {
     }
 
     public static Settings masterNode(final Settings settings) {
-        return addRoles(settings, Collections.singleton(DiscoveryNodeRole.MASTER_ROLE));
+        return addRoles(settings, Collections.singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE));
     }
 
     public static Settings masterOnlyNode() {
@@ -174,7 +181,7 @@ public class NodeRoles {
     }
 
     public static Settings masterOnlyNode(final Settings settings) {
-        return onlyRole(settings, DiscoveryNodeRole.MASTER_ROLE);
+        return onlyRole(settings, DiscoveryNodeRole.CLUSTER_MANAGER_ROLE);
     }
 
     public static Settings nonMasterNode() {
@@ -182,7 +189,7 @@ public class NodeRoles {
     }
 
     public static Settings nonMasterNode(final Settings settings) {
-        return removeRoles(settings, Collections.singleton(DiscoveryNodeRole.MASTER_ROLE));
+        return removeRoles(settings, Collections.singleton(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE));
     }
 
     public static Settings remoteClusterClientNode() {

test/framework/src/test/java/org/opensearch/test/test/InternalTestClusterTests.java

@@ -398,17 +398,19 @@ public class InternalTestClusterTests extends OpenSearchTestCase {
             Function.identity()
         );
         cluster.beforeTest(random());
+        // TODO: Remove this line, and replace 'clusterManagerRole' with CLUSTER_MANAGER_ROLE, after MASTER_ROLE is removed.
+        // It is added in 2.0, along with the introduction of CLUSTER_MANAGER_ROLE, aims to test the 2 roles have the same effect.
+        DiscoveryNodeRole clusterManagerRole = randomFrom(DiscoveryNodeRole.CLUSTER_MANAGER_ROLE, DiscoveryNodeRole.MASTER_ROLE);
         List<DiscoveryNodeRole> roles = new ArrayList<>();
         for (int i = 0; i < numNodes; i++) {
-            final DiscoveryNodeRole role = i == numNodes - 1 && roles.contains(DiscoveryNodeRole.MASTER_ROLE) == false
+            final DiscoveryNodeRole role = i == numNodes - 1 && roles.contains(clusterManagerRole) == false
-                ? DiscoveryNodeRole.MASTER_ROLE
+                ? clusterManagerRole  // last node and still no master
-                : // last node and still no master
+                : randomFrom(clusterManagerRole, DiscoveryNodeRole.DATA_ROLE, DiscoveryNodeRole.INGEST_ROLE);
-                randomFrom(DiscoveryNodeRole.MASTER_ROLE, DiscoveryNodeRole.DATA_ROLE, DiscoveryNodeRole.INGEST_ROLE);
             roles.add(role);
         }
 
         cluster.setBootstrapMasterNodeIndex(
-            randomIntBetween(0, (int) roles.stream().filter(role -> role.equals(DiscoveryNodeRole.MASTER_ROLE)).count() - 1)
+            randomIntBetween(0, (int) roles.stream().filter(role -> role.equals(clusterManagerRole)).count() - 1)
         );
 
         try {
@@ -416,7 +418,7 @@ public class InternalTestClusterTests extends OpenSearchTestCase {
             for (int i = 0; i < numNodes; i++) {
                 final DiscoveryNodeRole role = roles.get(i);
                 final String node;
-                if (role == DiscoveryNodeRole.MASTER_ROLE) {
+                if (role == clusterManagerRole) {
                     node = cluster.startMasterOnlyNode();
                 } else if (role == DiscoveryNodeRole.DATA_ROLE) {
                     node = cluster.startDataOnlyNode();
@@ -438,7 +440,7 @@ public class InternalTestClusterTests extends OpenSearchTestCase {
                 DiscoveryNode node = cluster.getInstance(ClusterService.class, name).localNode();
                 List<String> paths = Arrays.stream(getNodePaths(cluster, name)).map(Path::toString).collect(Collectors.toList());
                 if (node.isMasterNode()) {
-                    result.computeIfAbsent(DiscoveryNodeRole.MASTER_ROLE, k -> new HashSet<>()).addAll(paths);
+                    result.computeIfAbsent(clusterManagerRole, k -> new HashSet<>()).addAll(paths);
                 } else if (node.isDataNode()) {
                     result.computeIfAbsent(DiscoveryNodeRole.DATA_ROLE, k -> new HashSet<>()).addAll(paths);
                 } else {