Assign follower primary to nodes with remote cluster client role (ela…

…stic#59375)

The primary shards of follower indices during the bootstrap need to be
on nodes with the remote cluster client role as those nodes reach out to
the corresponding leader shards on the remote cluster to copy Lucene
segment files and renew the retention leases. This commit introduces a
new allocation decider that ensures bootstrapping follower primaries are
allocated to nodes with the remote cluster client role.

Relates elastic#54146
Relates elastic#53924
Closes elastic#58534

Co-authored-by: Jason Tedor <[email protected]>

x-pack/plugin/ccr/src/internalClusterTest/java/org/elasticsearch/xpack/ccr/PrimaryFollowerAllocationIT.java

@@ -0,0 +1,138 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+
+package org.elasticsearch.xpack.ccr;
+
+import org.elasticsearch.action.admin.cluster.allocation.ClusterAllocationExplanation;
+import org.elasticsearch.action.support.ActiveShardCount;
+import org.elasticsearch.cluster.ClusterState;
+import org.elasticsearch.cluster.node.DiscoveryNode;
+import org.elasticsearch.cluster.node.DiscoveryNodeRole;
+import org.elasticsearch.cluster.routing.IndexShardRoutingTable;
+import org.elasticsearch.cluster.routing.ShardRouting;
+import org.elasticsearch.cluster.routing.allocation.AllocationDecision;
+import org.elasticsearch.cluster.routing.allocation.NodeAllocationResult;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.unit.TimeValue;
+import org.elasticsearch.common.util.set.Sets;
+import org.elasticsearch.common.xcontent.XContentType;
+import org.elasticsearch.test.NodeRoles;
+import org.elasticsearch.xpack.CcrIntegTestCase;
+import org.elasticsearch.xpack.core.ccr.action.PutFollowAction;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertAcked;
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.in;
+
+public class PrimaryFollowerAllocationIT extends CcrIntegTestCase {
+
+    @Override
+    protected boolean reuseClusters() {
+        return false;
+    }
+
+    public void testDoNotAllocateFollowerPrimaryToNodesWithoutRemoteClusterClientRole() throws Exception {
+        final String leaderIndex = "leader-not-allow-index";
+        final String followerIndex = "follower-not-allow-index";
+        final List<String> dataOnlyNodes = getFollowerCluster().startNodes(between(1, 2),
+            NodeRoles.onlyRoles(Collections.singleton(DiscoveryNodeRole.DATA_ROLE)));
+        assertAcked(leaderClient().admin().indices().prepareCreate(leaderIndex)
+            .setSource(getIndexSettings(between(1, 2), between(0, 1)), XContentType.JSON));
+        final PutFollowAction.Request putFollowRequest = putFollow(leaderIndex, followerIndex);
+        putFollowRequest.setSettings(Settings.builder()
+            .put("index.routing.allocation.include._name", String.join(",", dataOnlyNodes))
+            .build());
+        putFollowRequest.waitForActiveShards(ActiveShardCount.ONE);
+        putFollowRequest.timeout(TimeValue.timeValueSeconds(2));
+        final PutFollowAction.Response response = followerClient().execute(PutFollowAction.INSTANCE, putFollowRequest).get();
+        assertFalse(response.isFollowIndexShardsAcked());
+        assertFalse(response.isIndexFollowingStarted());
+        final ClusterAllocationExplanation explanation = followerClient().admin().cluster().prepareAllocationExplain()
+            .setIndex(followerIndex).setShard(0).setPrimary(true).get().getExplanation();
+        for (NodeAllocationResult nodeDecision : explanation.getShardAllocationDecision().getAllocateDecision().getNodeDecisions()) {
+            assertThat(nodeDecision.getNodeDecision(), equalTo(AllocationDecision.NO));
+            if (dataOnlyNodes.contains(nodeDecision.getNode().getName())) {
+                final List<String> decisions = nodeDecision.getCanAllocateDecision().getDecisions()
+                    .stream().map(Object::toString).collect(Collectors.toList());
+                assertThat("NO(shard is a primary follower and being bootstrapped, but node does not have the remote_cluster_client role)",
+                    in(decisions));
+            }
+        }
+    }
+
+    public void testAllocateFollowerPrimaryToNodesWithRemoteClusterClientRole() throws Exception {
+        final String leaderIndex = "leader-allow-index";
+        final String followerIndex = "follower-allow-index";
+        final List<String> dataOnlyNodes = getFollowerCluster().startNodes(between(2, 3),
+            NodeRoles.onlyRoles(Collections.singleton(DiscoveryNodeRole.DATA_ROLE)));
+        final List<String> dataAndRemoteNodes = getFollowerCluster().startNodes(between(1, 2),
+            NodeRoles.onlyRoles(Sets.newHashSet(DiscoveryNodeRole.DATA_ROLE, DiscoveryNodeRole.REMOTE_CLUSTER_CLIENT_ROLE)));
+        assertAcked(leaderClient().admin().indices().prepareCreate(leaderIndex)
+            .setSource(getIndexSettings(between(1, 2), between(0, 1)), XContentType.JSON));
+        final PutFollowAction.Request putFollowRequest = putFollow(leaderIndex, followerIndex);
+        putFollowRequest.setSettings(Settings.builder()
+            .put("index.routing.rebalance.enable", "none")
+            .put("index.routing.allocation.include._name",
+                Stream.concat(dataOnlyNodes.stream(), dataAndRemoteNodes.stream()).collect(Collectors.joining(",")))
+            .build());
+        final PutFollowAction.Response response = followerClient().execute(PutFollowAction.INSTANCE, putFollowRequest).get();
+        assertTrue(response.isFollowIndexShardsAcked());
+        assertTrue(response.isIndexFollowingStarted());
+        ensureFollowerGreen(followerIndex);
+        int numDocs = between(0, 20);
+        for (int i = 0; i < numDocs; i++) {
+            leaderClient().prepareIndex(leaderIndex, "_doc").setSource("f", i).get();
+        }
+        // Empty follower primaries must be assigned to nodes with the remote cluster client role
+        assertBusy(() -> {
+            final ClusterState state = getFollowerCluster().client().admin().cluster().prepareState().get().getState();
+            for (IndexShardRoutingTable shardRoutingTable : state.routingTable().index(followerIndex)) {
+                final ShardRouting primaryShard = shardRoutingTable.primaryShard();
+                assertTrue(primaryShard.assignedToNode());
+                final DiscoveryNode assignedNode = state.nodes().get(primaryShard.currentNodeId());
+                assertThat(assignedNode.getName(), in(dataAndRemoteNodes));
+            }
+        });
+        // Follower primaries can be relocated to nodes without the remote cluster client role
+        followerClient().admin().indices().prepareUpdateSettings(followerIndex)
+            .setSettings(Settings.builder().put("index.routing.allocation.include._name", String.join(",", dataOnlyNodes)))
+            .get();
+        assertBusy(() -> {
+            final ClusterState state = getFollowerCluster().client().admin().cluster().prepareState().get().getState();
+            for (IndexShardRoutingTable shardRoutingTable : state.routingTable().index(followerIndex)) {
+                for (ShardRouting shard : shardRoutingTable) {
+                    assertNotNull(shard.currentNodeId());
+                    final DiscoveryNode assignedNode = state.nodes().get(shard.currentNodeId());
+                    assertThat(assignedNode.getName(), in(dataOnlyNodes));
+                }
+            }
+        });
+        assertIndexFullyReplicatedToFollower(leaderIndex, followerIndex);
+        // Follower primaries can be recovered from the existing copies on nodes without the remote cluster client role
+        getFollowerCluster().fullRestart();
+        ensureFollowerGreen(followerIndex);
+        assertBusy(() -> {
+            final ClusterState state = getFollowerCluster().client().admin().cluster().prepareState().get().getState();
+            for (IndexShardRoutingTable shardRoutingTable : state.routingTable().index(followerIndex)) {
+                for (ShardRouting shard : shardRoutingTable) {
+                    assertNotNull(shard.currentNodeId());
+                    final DiscoveryNode assignedNode = state.nodes().get(shard.currentNodeId());
+                    assertThat(assignedNode.getName(), in(dataOnlyNodes));
+                }
+            }
+        });
+        int moreDocs = between(0, 20);
+        for (int i = 0; i < moreDocs; i++) {
+            leaderClient().prepareIndex(leaderIndex, "_doc").setSource("f", i).get();
+        }
+        assertIndexFullyReplicatedToFollower(leaderIndex, followerIndex);
+    }
+}

x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/Ccr.java

@@ -16,6 +16,7 @@
 import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;
 import org.elasticsearch.cluster.metadata.Metadata;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
+import org.elasticsearch.cluster.routing.allocation.decider.AllocationDecider;
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.ParseField;
 import org.elasticsearch.common.inject.Module;
@@ -36,6 +37,7 @@
 import org.elasticsearch.persistent.PersistentTaskParams;
 import org.elasticsearch.persistent.PersistentTasksExecutor;
 import org.elasticsearch.plugins.ActionPlugin;
+import org.elasticsearch.plugins.ClusterPlugin;
 import org.elasticsearch.plugins.EnginePlugin;
 import org.elasticsearch.plugins.PersistentTaskPlugin;
 import org.elasticsearch.plugins.Plugin;
@@ -75,6 +77,7 @@
 import org.elasticsearch.xpack.ccr.action.repositories.GetCcrRestoreFileChunkAction;
 import org.elasticsearch.xpack.ccr.action.repositories.PutCcrRestoreSessionAction;
 import org.elasticsearch.xpack.ccr.action.repositories.PutInternalCcrRepositoryAction;
+import org.elasticsearch.xpack.ccr.allocation.CcrPrimaryFollowerAllocationDecider;
 import org.elasticsearch.xpack.ccr.index.engine.FollowingEngineFactory;
 import org.elasticsearch.xpack.ccr.repository.CcrRepository;
 import org.elasticsearch.xpack.ccr.repository.CcrRestoreSourceService;
@@ -124,7 +127,7 @@
 /**
  * Container class for CCR functionality.
  */
-public class Ccr extends Plugin implements ActionPlugin, PersistentTaskPlugin, EnginePlugin, RepositoryPlugin {
+public class Ccr extends Plugin implements ActionPlugin, PersistentTaskPlugin, EnginePlugin, RepositoryPlugin, ClusterPlugin {
 
     public static final String CCR_THREAD_POOL_NAME = "ccr";
     public static final String CCR_CUSTOM_METADATA_KEY = "ccr";
@@ -375,4 +378,9 @@ public Collection<RequestValidators.RequestValidator<PutMappingRequest>> mapping
     public Collection<RequestValidators.RequestValidator<IndicesAliasesRequest>> indicesAliasesRequestValidators() {
         return Collections.singletonList(CcrRequests.CCR_INDICES_ALIASES_REQUEST_VALIDATOR);
     }
+
+    @Override
+    public Collection<AllocationDecider> createAllocationDeciders(Settings settings, ClusterSettings clusterSettings) {
+        return List.of(new CcrPrimaryFollowerAllocationDecider());
+    }
 }

x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/allocation/CcrPrimaryFollowerAllocationDecider.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+
+/*
+ * 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.xpack.ccr.allocation;
+
+import org.elasticsearch.cluster.metadata.IndexMetadata;
+import org.elasticsearch.cluster.node.DiscoveryNodeRole;
+import org.elasticsearch.cluster.routing.RecoverySource;
+import org.elasticsearch.cluster.routing.RoutingNode;
+import org.elasticsearch.cluster.routing.ShardRouting;
+import org.elasticsearch.cluster.routing.allocation.RoutingAllocation;
+import org.elasticsearch.cluster.routing.allocation.decider.AllocationDecider;
+import org.elasticsearch.cluster.routing.allocation.decider.Decision;
+import org.elasticsearch.xpack.ccr.CcrSettings;
+
+/**
+ * An allocation decider that ensures primary shards of follower indices that are being bootstrapped are assigned to nodes that have the
+ * remote cluster client role. This is necessary as those nodes reach out to the leader shards on the remote cluster to copy Lucene segment
+ * files and periodically renew retention leases during the bootstrap.
+ */
+public final class CcrPrimaryFollowerAllocationDecider extends AllocationDecider {
+    static final String NAME = "ccr_primary_follower";
+
+    @Override
+    public Decision canAllocate(ShardRouting shardRouting, RoutingNode node, RoutingAllocation allocation) {
+        final IndexMetadata indexMetadata = allocation.metadata().index(shardRouting.index());
+        if (CcrSettings.CCR_FOLLOWING_INDEX_SETTING.get(indexMetadata.getSettings()) == false) {
+            return allocation.decision(Decision.YES, NAME, "shard is not a follower and is not under the purview of this decider");
+        }
+        if (shardRouting.primary() == false) {
+            return allocation.decision(Decision.YES, NAME, "shard is a replica follower and is not under the purview of this decider");
+        }
+        final RecoverySource recoverySource = shardRouting.recoverySource();
+        if (recoverySource == null || recoverySource.getType() != RecoverySource.Type.SNAPSHOT) {
+            return allocation.decision(Decision.YES, NAME,
+                "shard is a primary follower but was bootstrapped already; hence is not under the purview of this decider");
+        }
+        if (node.node().isRemoteClusterClient() == false) {
+            return allocation.decision(Decision.NO, NAME, "shard is a primary follower and being bootstrapped, but node does not have the "
+                + DiscoveryNodeRole.REMOTE_CLUSTER_CLIENT_ROLE.roleName() + " role");
+        }
+        return allocation.decision(Decision.YES, NAME,
+            "shard is a primary follower and node has the " + DiscoveryNodeRole.REMOTE_CLUSTER_CLIENT_ROLE.roleName() + " role");
+    }
+}