Enable ClusterInfoService by default

Since we enabled the disk threshold decider by default, we need to
enable the cluster info service so that disk usages and shard sizes can
be gathered also.

Adds a test that checks that we are gathering information by default.

src/main/java/org/elasticsearch/cluster/InternalClusterInfoService.java

@@ -84,7 +84,7 @@ public final class InternalClusterInfoService extends AbstractComponent implemen
         this.clusterService = clusterService;
         this.threadPool = threadPool;
         this.updateFrequency = settings.getAsTime(INTERNAL_CLUSTER_INFO_UPDATE_INTERVAL, TimeValue.timeValueSeconds(30));
-        this.enabled = settings.getAsBoolean(DiskThresholdDecider.CLUSTER_ROUTING_ALLOCATION_DISK_THRESHOLD_ENABLED, false);
+        this.enabled = settings.getAsBoolean(DiskThresholdDecider.CLUSTER_ROUTING_ALLOCATION_DISK_THRESHOLD_ENABLED, true);
         nodeSettingsService.addListener(new ApplySettings());
 
         // Add InternalClusterInfoService to listen for Master changes

src/test/java/org/elasticsearch/cluster/routing/ClusterInfoServiceTests.java

@@ -0,0 +1,73 @@
+/*
+ * 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.cluster.ClusterInfo;
+import org.elasticsearch.cluster.ClusterInfoService;
+import org.elasticsearch.cluster.DiskUsage;
+import org.elasticsearch.cluster.InternalClusterInfoService;
+import org.elasticsearch.common.settings.ImmutableSettings;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.test.ElasticsearchIntegrationTest;
+import org.elasticsearch.test.InternalTestCluster;
+import org.junit.Test;
+
+import java.util.Map;
+
+import static org.hamcrest.Matchers.greaterThan;
+
+/**
+ * Integration tests for the ClusterInfoService collecting information
+ */
+@ElasticsearchIntegrationTest.ClusterScope(scope= ElasticsearchIntegrationTest.Scope.SUITE, numDataNodes =0)
+public class ClusterInfoServiceTests extends ElasticsearchIntegrationTest {
+
+    @Override
+    protected Settings nodeSettings(int nodeOrdinal) {
+        return ImmutableSettings.builder()
+                .put(InternalClusterInfoService.INTERNAL_CLUSTER_INFO_UPDATE_INTERVAL, "1s")
+                .build();
+    }
+
+    @Test
+    public void testClusterInfoServiceCollectsInformation() throws Exception {
+        createIndex("test");
+        ensureGreen("test");
+        Thread.sleep(2000); // wait 2 seconds for new information to be gathered
+        InternalTestCluster internalTestCluster = internalCluster();
+        // Get the cluster info service on the master node
+        ClusterInfoService infoService = internalTestCluster.getInstance(ClusterInfoService.class, internalTestCluster.getMasterName());
+        ClusterInfo info = infoService.getClusterInfo();
+        Map<String, DiskUsage> usages = info.getNodeDiskUsages();
+        Map<String, Long> shardSizes = info.getShardSizes();
+        assertNotNull(usages);
+        assertNotNull(shardSizes);
+        assertThat("some usages are populated", usages.values().size(), greaterThan(0));
+        assertThat("some shard sizes are populated", shardSizes.values().size(), greaterThan(0));
+        for (DiskUsage usage : usages.values()) {
+            logger.info("--> usage: {}", usage);
+            assertThat("usage has be retrieved", usage.getFreeBytes(), greaterThan(0L));
+        }
+        for (Long size : shardSizes.values()) {
+            logger.info("--> shard size: {}", size);
+            assertThat("shard size is greater than 0", size, greaterThan(0L));
+        }
+    }
+}