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Add allocation decider for mixed cluster during remote store migration (
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opensearch-project#12505)

Signed-off-by: Lakshya Taragi <[email protected]>
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ltaragi authored Mar 15, 2024
1 parent ef50fb4 commit 18e5816
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import org.opensearch.cluster.routing.allocation.decider.NodeLoadAwareAllocationDecider;
import org.opensearch.cluster.routing.allocation.decider.NodeVersionAllocationDecider;
import org.opensearch.cluster.routing.allocation.decider.RebalanceOnlyWhenActiveAllocationDecider;
import org.opensearch.cluster.routing.allocation.decider.RemoteStoreMigrationAllocationDecider;
import org.opensearch.cluster.routing.allocation.decider.ReplicaAfterPrimaryActiveAllocationDecider;
import org.opensearch.cluster.routing.allocation.decider.ResizeAllocationDecider;
import org.opensearch.cluster.routing.allocation.decider.RestoreInProgressAllocationDecider;
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import org.opensearch.common.settings.Setting;
import org.opensearch.common.settings.Setting.Property;
import org.opensearch.common.settings.Settings;
import org.opensearch.common.util.FeatureFlags;
import org.opensearch.common.util.concurrent.ThreadContext;
import org.opensearch.common.util.set.Sets;
import org.opensearch.core.ParseField;
Expand Down Expand Up @@ -373,6 +375,9 @@ public static Collection<AllocationDecider> createAllocationDeciders(
addAllocationDecider(deciders, new AwarenessAllocationDecider(settings, clusterSettings));
addAllocationDecider(deciders, new NodeLoadAwareAllocationDecider(settings, clusterSettings));
addAllocationDecider(deciders, new TargetPoolAllocationDecider());
if (FeatureFlags.isEnabled(FeatureFlags.REMOTE_STORE_MIGRATION_EXPERIMENTAL_SETTING)) {
addAllocationDecider(deciders, new RemoteStoreMigrationAllocationDecider(settings, clusterSettings));
}

clusterPlugins.stream()
.flatMap(p -> p.createAllocationDeciders(settings, clusterSettings).stream())
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/*
* 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.
*/

/*
* 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.
*/

/*
* Modifications Copyright OpenSearch Contributors. See
* GitHub history for details.
*/

package org.opensearch.cluster.routing.allocation.decider;

import org.opensearch.cluster.metadata.IndexMetadata;
import org.opensearch.cluster.node.DiscoveryNode;
import org.opensearch.cluster.routing.RoutingNode;
import org.opensearch.cluster.routing.ShardRouting;
import org.opensearch.cluster.routing.allocation.RoutingAllocation;
import org.opensearch.common.settings.ClusterSettings;
import org.opensearch.common.settings.Settings;
import org.opensearch.node.remotestore.RemoteStoreNodeService;
import org.opensearch.node.remotestore.RemoteStoreNodeService.CompatibilityMode;
import org.opensearch.node.remotestore.RemoteStoreNodeService.Direction;

import java.util.Locale;

/**
* A new allocation decider for migration of document replication clusters to remote store backed clusters:
* - For STRICT compatibility mode, the decision is always YES
* - For remote store backed indices, relocation or allocation/relocation can only be towards a remote node
* - For "REMOTE_STORE" migration direction:
* - New primary shards can only be allocated to a remote node
* - New replica shards can be allocated to a remote node iff the primary has been migrated/allocated to a remote node
* - For other directions ("DOCREP", "NONE"), the decision is always YES
*
* @opensearch.internal
*/
public class RemoteStoreMigrationAllocationDecider extends AllocationDecider {

public static final String NAME = "remote_store_migration";

private Direction migrationDirection;
private CompatibilityMode compatibilityMode;
private boolean remoteStoreBackedIndex;

public RemoteStoreMigrationAllocationDecider(Settings settings, ClusterSettings clusterSettings) {
this.migrationDirection = RemoteStoreNodeService.MIGRATION_DIRECTION_SETTING.get(settings);
this.compatibilityMode = RemoteStoreNodeService.REMOTE_STORE_COMPATIBILITY_MODE_SETTING.get(settings);
clusterSettings.addSettingsUpdateConsumer(RemoteStoreNodeService.MIGRATION_DIRECTION_SETTING, this::setMigrationDirection);
clusterSettings.addSettingsUpdateConsumer(
RemoteStoreNodeService.REMOTE_STORE_COMPATIBILITY_MODE_SETTING,
this::setCompatibilityMode
);
}

private void setMigrationDirection(Direction migrationDirection) {
this.migrationDirection = migrationDirection;
}

private void setCompatibilityMode(CompatibilityMode compatibilityMode) {
this.compatibilityMode = compatibilityMode;
}

@Override
public Decision canAllocate(ShardRouting shardRouting, RoutingNode node, RoutingAllocation allocation) {
DiscoveryNode targetNode = node.node();

if (compatibilityMode.equals(CompatibilityMode.STRICT)) {
// assuming all nodes are of the same type (all remote or all non-remote)
return allocation.decision(
Decision.YES,
NAME,
getDecisionDetails(true, shardRouting, targetNode, " for strict compatibility mode")
);
}

if (migrationDirection.equals(Direction.REMOTE_STORE) == false) {
// docrep migration direction is currently not supported
return allocation.decision(
Decision.YES,
NAME,
getDecisionDetails(true, shardRouting, targetNode, " for non remote_store direction")
);
}

// check for remote store backed indices
IndexMetadata indexMetadata = allocation.metadata().getIndexSafe(shardRouting.index());
if (IndexMetadata.INDEX_REMOTE_STORE_ENABLED_SETTING.exists(indexMetadata.getSettings())) {
remoteStoreBackedIndex = IndexMetadata.INDEX_REMOTE_STORE_ENABLED_SETTING.get(indexMetadata.getSettings());
}
if (remoteStoreBackedIndex && targetNode.isRemoteStoreNode() == false) {
// allocations and relocations must be to a remote node
String reason = String.format(
Locale.ROOT,
" because a remote store backed index's shard copy can only be %s to a remote node",
((shardRouting.assignedToNode() == false) ? "allocated" : "relocated")
);
return allocation.decision(Decision.NO, NAME, getDecisionDetails(false, shardRouting, targetNode, reason));
}

if (shardRouting.primary()) {
return primaryShardDecision(shardRouting, targetNode, allocation);
}
return replicaShardDecision(shardRouting, targetNode, allocation);
}

// handle scenarios for allocation of a new shard's primary copy
private Decision primaryShardDecision(ShardRouting primaryShardRouting, DiscoveryNode targetNode, RoutingAllocation allocation) {
if (targetNode.isRemoteStoreNode() == false) {
return allocation.decision(Decision.NO, NAME, getDecisionDetails(false, primaryShardRouting, targetNode, ""));
}
return allocation.decision(Decision.YES, NAME, getDecisionDetails(true, primaryShardRouting, targetNode, ""));
}

private Decision replicaShardDecision(ShardRouting replicaShardRouting, DiscoveryNode targetNode, RoutingAllocation allocation) {
if (targetNode.isRemoteStoreNode()) {
ShardRouting primaryShardRouting = allocation.routingNodes().activePrimary(replicaShardRouting.shardId());
boolean primaryHasMigratedToRemote = false;
if (primaryShardRouting != null) {
DiscoveryNode primaryShardNode = allocation.nodes().getNodes().get(primaryShardRouting.currentNodeId());
primaryHasMigratedToRemote = primaryShardNode.isRemoteStoreNode();
}
if (primaryHasMigratedToRemote == false) {
return allocation.decision(
Decision.NO,
NAME,
getDecisionDetails(false, replicaShardRouting, targetNode, " since primary shard copy is not yet migrated to remote")
);
}
return allocation.decision(
Decision.YES,
NAME,
getDecisionDetails(true, replicaShardRouting, targetNode, " since primary shard copy has been migrated to remote")
);
}
return allocation.decision(Decision.YES, NAME, getDecisionDetails(true, replicaShardRouting, targetNode, ""));
}

// get detailed reason for the decision
private String getDecisionDetails(boolean isYes, ShardRouting shardRouting, DiscoveryNode targetNode, String reason) {
return String.format(
Locale.ROOT,
"[%s migration_direction]: %s shard copy %s be %s to a %s node%s",
migrationDirection.direction,
(shardRouting.primary() ? "primary" : "replica"),
(isYes ? "can" : "can not"),
((shardRouting.assignedToNode() == false) ? "allocated" : "relocated"),
(targetNode.isRemoteStoreNode() ? "remote" : "non-remote"),
reason
);
}

}
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Expand Up @@ -51,6 +51,7 @@
import org.opensearch.cluster.routing.allocation.decider.NodeLoadAwareAllocationDecider;
import org.opensearch.cluster.routing.allocation.decider.NodeVersionAllocationDecider;
import org.opensearch.cluster.routing.allocation.decider.RebalanceOnlyWhenActiveAllocationDecider;
import org.opensearch.cluster.routing.allocation.decider.RemoteStoreMigrationAllocationDecider;
import org.opensearch.cluster.routing.allocation.decider.ReplicaAfterPrimaryActiveAllocationDecider;
import org.opensearch.cluster.routing.allocation.decider.ResizeAllocationDecider;
import org.opensearch.cluster.routing.allocation.decider.RestoreInProgressAllocationDecider;
Expand All @@ -67,6 +68,7 @@
import org.opensearch.common.settings.Setting.Property;
import org.opensearch.common.settings.Settings;
import org.opensearch.common.settings.SettingsModule;
import org.opensearch.common.util.FeatureFlags;
import org.opensearch.common.util.concurrent.ThreadContext;
import org.opensearch.gateway.GatewayAllocator;
import org.opensearch.plugins.ClusterPlugin;
Expand Down Expand Up @@ -242,6 +244,9 @@ public void testAllocationDeciderOrder() {
NodeLoadAwareAllocationDecider.class,
TargetPoolAllocationDecider.class
);
if (FeatureFlags.isEnabled(FeatureFlags.REMOTE_STORE_MIGRATION_EXPERIMENTAL_SETTING)) {
expectedDeciders.add(RemoteStoreMigrationAllocationDecider.class);
}
Collection<AllocationDecider> deciders = ClusterModule.createAllocationDeciders(
Settings.EMPTY,
new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS),
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