Add a system property to ignore awareness attributes (#46375)

This is a follow up of #19191 for 7.x.
This change adds a system property called "es.routing.search_ignore_awareness_attributes" that when set to true will
effectively ignore allocation awareness attributes when routing search and get requests. This is now the default in 8.x so this
commit adds a way to opt-in to this new behavior in a minor version of 7.x.

Relates #45735

docs/reference/modules/cluster/allocation_awareness.asciidoc

@@ -17,9 +17,12 @@ The allocation awareness settings can be configured in
 `elasticsearch.yml` and updated dynamically with the
 <<cluster-update-settings,cluster-update-settings>> API.
 
-{es} prefers using shards in the same location (with the same
-awareness attribute values) to process search or GET requests. Using local
-shards is usually faster than crossing rack or zone boundaries.
+By default {es} uses <<search-adaptive-replica,adaptive replica selection>>
+to route search or GET requests. However, with the presence of allocation awareness
+attributes {es} will prefer using shards in the same location (with the same
+awareness attribute values) to process these requests. This behavior can be
+disabled by specifying `export ES_JAVA_OPTS="$ES_JAVA_OPTS -Des.search.ignore_awareness_attributes=true"`
+system property on every node that is part of the cluster.
 
 NOTE: The number of attribute values determines how many shard copies are
 allocated in each location. If the number of nodes in each location is

qa/evil-tests/src/test/java/org/elasticsearch/cluster/routing/EvilSystemPropertyTests.java

@@ -0,0 +1,49 @@
+/*
+ * 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.cluster.routing;
+
+import org.elasticsearch.common.SuppressForbidden;
+import org.elasticsearch.common.settings.ClusterSettings;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.test.ESTestCase;
+
+import static org.hamcrest.Matchers.equalTo;
+
+public class EvilSystemPropertyTests extends ESTestCase {
+
+    @SuppressForbidden(reason = "manipulates system properties for testing")
+    public void testDisableSearchAllocationAwareness() {
+        Settings indexSettings = Settings.builder()
+            .put("cluster.routing.allocation.awareness.attributes", "test")
+            .build();
+        OperationRouting routing = new OperationRouting(indexSettings,
+            new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS));
+        assertThat(routing.getAwarenessAttributes().size(), equalTo(1));
+        assertThat(routing.getAwarenessAttributes().get(0), equalTo("test"));
+        System.setProperty("es.search.ignore_awareness_attributes", "true");
+        try {
+            routing = new OperationRouting(indexSettings,
+                new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS));
+            assertTrue(routing.getAwarenessAttributes().isEmpty());
+        } finally {
+            System.clearProperty("es.search.ignore_awareness_attributes");
+        }
+
+    }
+}

server/src/main/java/org/elasticsearch/cluster/routing/OperationRouting.java

@@ -42,6 +42,8 @@ import java.util.Map;
 import java.util.Set;
 import java.util.stream.Collectors;
 
+import static org.elasticsearch.common.Booleans.parseBoolean;
+
 public class OperationRouting {
 
     public static final Setting<Boolean> USE_ADAPTIVE_REPLICA_SELECTION_SETTING =
@@ -52,10 +54,17 @@ public class OperationRouting {
     private boolean useAdaptiveReplicaSelection;
 
     public OperationRouting(Settings settings, ClusterSettings clusterSettings) {
-        this.awarenessAttributes = AwarenessAllocationDecider.CLUSTER_ROUTING_ALLOCATION_AWARENESS_ATTRIBUTE_SETTING.get(settings);
+        // whether to ignore awareness attributes when routing requests
+        boolean ignoreAwarenessAttr = parseBoolean(System.getProperty("es.search.ignore_awareness_attributes"), false);
+        if (ignoreAwarenessAttr == false) {
+            awarenessAttributes = AwarenessAllocationDecider.CLUSTER_ROUTING_ALLOCATION_AWARENESS_ATTRIBUTE_SETTING.get(settings);
+            clusterSettings.addSettingsUpdateConsumer(AwarenessAllocationDecider.CLUSTER_ROUTING_ALLOCATION_AWARENESS_ATTRIBUTE_SETTING,
+                this::setAwarenessAttributes);
+        } else {
+            awarenessAttributes = Collections.emptyList();
+        }
+
         this.useAdaptiveReplicaSelection = USE_ADAPTIVE_REPLICA_SELECTION_SETTING.get(settings);
-        clusterSettings.addSettingsUpdateConsumer(AwarenessAllocationDecider.CLUSTER_ROUTING_ALLOCATION_AWARENESS_ATTRIBUTE_SETTING,
-            this::setAwarenessAttributes);
         clusterSettings.addSettingsUpdateConsumer(USE_ADAPTIVE_REPLICA_SELECTION_SETTING, this::setUseAdaptiveReplicaSelection);
     }
 
@@ -63,6 +72,10 @@ public class OperationRouting {
         this.useAdaptiveReplicaSelection = useAdaptiveReplicaSelection;
     }
 
+    List<String> getAwarenessAttributes() {
+        return awarenessAttributes;
+    }
+
     private void setAwarenessAttributes(List<String> awarenessAttributes) {
         this.awarenessAttributes = awarenessAttributes;
     }