discovery-ec2 plugin should check `discovery.type`

As done in #13809 and in Azure, we should check that `discovery.type` is set to `ec2` before starting services.

Closes #13581.

plugins/discovery-ec2/src/main/java/org/elasticsearch/cloud/aws/Ec2Module.java

@@ -20,6 +20,9 @@
 package org.elasticsearch.cloud.aws;
 
 import org.elasticsearch.common.inject.AbstractModule;
+import org.elasticsearch.common.logging.ESLogger;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.discovery.ec2.Ec2Discovery;
 
 public class Ec2Module extends AbstractModule {
 
@@ -27,4 +30,18 @@ public class Ec2Module extends AbstractModule {
     protected void configure() {
         bind(AwsEc2Service.class).to(AwsEc2ServiceImpl.class).asEagerSingleton();
     }
+
+    /**
+     * Check if discovery is meant to start
+     * @return true if we can start discovery features
+     */
+    public static boolean isEc2DiscoveryActive(Settings settings, ESLogger logger) {
+        // User set discovery.type: ec2
+        if (!Ec2Discovery.EC2.equalsIgnoreCase(settings.get("discovery.type"))) {
+            logger.trace("discovery.type not set to {}", Ec2Discovery.EC2);
+            return false;
+        }
+
+        return true;
+    }
 }

plugins/discovery-ec2/src/main/java/org/elasticsearch/discovery/ec2/Ec2Discovery.java

@@ -21,8 +21,6 @@ package org.elasticsearch.discovery.ec2;
 
 import org.elasticsearch.cluster.ClusterName;
 import org.elasticsearch.cluster.ClusterService;
-import org.elasticsearch.cluster.settings.ClusterDynamicSettings;
-import org.elasticsearch.cluster.settings.DynamicSettings;
 import org.elasticsearch.common.inject.Inject;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.discovery.DiscoverySettings;
@@ -38,6 +36,8 @@ import org.elasticsearch.transport.TransportService;
  */
 public class Ec2Discovery extends ZenDiscovery {
 
+    public static final String EC2 = "ec2";
+
     @Inject
     public Ec2Discovery(Settings settings, ClusterName clusterName, ThreadPool threadPool, TransportService transportService,
                         ClusterService clusterService, NodeSettingsService nodeSettingsService, ZenPingService pingService,

plugins/discovery-ec2/src/main/java/org/elasticsearch/plugin/discovery/ec2/Ec2DiscoveryPlugin.java

@@ -23,6 +23,9 @@ import org.elasticsearch.cloud.aws.AwsEc2ServiceImpl;
 import org.elasticsearch.cloud.aws.Ec2Module;
 import org.elasticsearch.common.component.LifecycleComponent;
 import org.elasticsearch.common.inject.Module;
+import org.elasticsearch.common.logging.ESLogger;
+import org.elasticsearch.common.logging.Loggers;
+import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.discovery.DiscoveryModule;
 import org.elasticsearch.discovery.ec2.AwsEc2UnicastHostsProvider;
 import org.elasticsearch.discovery.ec2.Ec2Discovery;
@@ -55,6 +58,13 @@ public class Ec2DiscoveryPlugin extends Plugin {
         });
     }
 
+    private final Settings settings;
+    protected final ESLogger logger = Loggers.getLogger(Ec2DiscoveryPlugin.class);
+
+    public Ec2DiscoveryPlugin(Settings settings) {
+        this.settings = settings;
+    }
+
     @Override
     public String name() {
         return "discovery-ec2";
@@ -80,7 +90,9 @@ public class Ec2DiscoveryPlugin extends Plugin {
     }
 
     public void onModule(DiscoveryModule discoveryModule) {
-        discoveryModule.addDiscoveryType("ec2", Ec2Discovery.class);
-        discoveryModule.addUnicastHostProvider(AwsEc2UnicastHostsProvider.class);
+        if (Ec2Module.isEc2DiscoveryActive(settings, logger)) {
+            discoveryModule.addDiscoveryType("ec2", Ec2Discovery.class);
+            discoveryModule.addUnicastHostProvider(AwsEc2UnicastHostsProvider.class);
+        }
     }
 }

plugins/discovery-ec2/src/test/java/org/elasticsearch/discovery/ec2/Ec2DiscoverySettingsTests.java

@@ -0,0 +1,44 @@
+/*
+ * 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.discovery.ec2;
+
+import org.elasticsearch.cloud.aws.Ec2Module;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.test.ESTestCase;
+
+import static org.hamcrest.Matchers.is;
+
+public class Ec2DiscoverySettingsTests extends ESTestCase {
+
+    public void testDiscoveryReady() {
+        Settings settings = Settings.builder()
+                .put("discovery.type", "ec2")
+                .build();
+        boolean discoveryReady = Ec2Module.isEc2DiscoveryActive(settings, logger);
+        assertThat(discoveryReady, is(true));
+    }
+
+    public void testDiscoveryNotReady() {
+        Settings settings = Settings.EMPTY;
+        boolean discoveryReady = Ec2Module.isEc2DiscoveryActive(settings, logger);
+        assertThat(discoveryReady, is(false));
+    }
+
+}