Allow `_gce_` network when not using discovery gce

For now we support `_gce_` only if discovery is set to `gce` and all information about GCE is provided (project_id and zone).
But in some cases, people would like to only bind to `_gce_` on a single node (without any elasticsearch cluster).

They could access the machine then from other machines running inside the same project.

This commit adds a new GceMetadataService which is started as soon as the plugin is started so GceNameResolver can use it to resolve `_gce`.

Closes #15724.

plugins/discovery-gce/src/main/java/org/elasticsearch/cloud/gce/GceComputeService.java

@@ -76,19 +76,4 @@ public interface GceComputeService extends LifecycleComponent<GceComputeService>
      * @return a collection of running instances within the same GCE project
      */
     Collection<Instance> instances();
-
-    /**
-     * <p>Gets metadata on the current running machine (call to
-     * http://metadata.google.internal/computeMetadata/v1/instance/xxx).</p>
-     * <p>For example, you can retrieve network information by replacing xxx with:</p>
-     * <ul>
-     *     <li>`hostname` when we need to resolve the host name</li>
-     *     <li>`network-interfaces/0/ip` when we need to resolve private IP</li>
-     * </ul>
-     * @see org.elasticsearch.cloud.gce.network.GceNameResolver for bindings
-     * @param metadataPath path to metadata information
-     * @return extracted information (for example a hostname or an IP address)
-     * @throws IOException in case metadata URL is not accessible
-     */
-    String metadata(String metadataPath) throws IOException;
 }

plugins/discovery-gce/src/main/java/org/elasticsearch/cloud/gce/GceComputeServiceImpl.java

@@ -116,47 +116,6 @@ public class GceComputeServiceImpl extends AbstractLifecycleComponent<GceCompute
         return instances;
     }
 
-    @Override
-    public String metadata(String metadataPath) throws IOException {
-        String urlMetadataNetwork = this.metaDataUrl + "/" + metadataPath;
-        logger.debug("get metadata from [{}]", urlMetadataNetwork);
-        final URL url = new URL(urlMetadataNetwork);
-        HttpHeaders headers;
-        try {
-            // hack around code messiness in GCE code
-            // TODO: get this fixed
-            SecurityManager sm = System.getSecurityManager();
-            if (sm != null) {
-                sm.checkPermission(new SpecialPermission());
-            }
-            headers = AccessController.doPrivileged(new PrivilegedExceptionAction<HttpHeaders>() {
-                @Override
-                public HttpHeaders run() throws IOException {
-                    return new HttpHeaders();
-                }
-            });
-            GenericUrl genericUrl = AccessController.doPrivileged(new PrivilegedAction<GenericUrl>() {
-                @Override
-                public GenericUrl run() {
-                    return new GenericUrl(url);
-                }
-            });
-
-            // This is needed to query meta data: https://cloud.google.com/compute/docs/metadata
-            headers.put("Metadata-Flavor", "Google");
-            HttpResponse response;
-            response = getGceHttpTransport().createRequestFactory()
-                    .buildGetRequest(genericUrl)
-                    .setHeaders(headers)
-                    .execute();
-            String metadata = response.parseAsString();
-            logger.debug("metadata found [{}]", metadata);
-            return metadata;
-        } catch (Exception e) {
-            throw new IOException("failed to fetch metadata from [" + urlMetadataNetwork + "]", e);
-        }
-    }
-
     private Compute client;
     private TimeValue refreshInterval = null;
     private long lastRefresh;
@@ -168,17 +127,17 @@ public class GceComputeServiceImpl extends AbstractLifecycleComponent<GceCompute
     private JsonFactory gceJsonFactory;
 
     private final boolean validateCerts;
+
     @Inject
-    public GceComputeServiceImpl(Settings settings, NetworkService networkService) {
+    public GceComputeServiceImpl(Settings settings) {
         super(settings);
         this.project = PROJECT_SETTING.get(settings);
         this.zones = ZONE_SETTING.get(settings);
         this.gceHost = GCE_HOST.get(settings);
         this.metaDataUrl =  gceHost + "/computeMetadata/v1/instance";
         this.gceRootUrl = GCE_ROOT_URL.get(settings);
-        tokenServerEncodedUrl = metaDataUrl + "/service-accounts/default/token";
+        this.tokenServerEncodedUrl = metaDataUrl + "/service-accounts/default/token";
         this.validateCerts = GCE_VALIDATE_CERTIFICATES.get(settings);
-        networkService.addCustomNameResolver(new GceNameResolver(settings, this));
     }
 
     protected synchronized HttpTransport getGceHttpTransport() throws GeneralSecurityException, IOException {

plugins/discovery-gce/src/main/java/org/elasticsearch/cloud/gce/GceMetadataService.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.cloud.gce;
+
+import org.elasticsearch.common.component.LifecycleComponent;
+
+import java.io.IOException;
+
+/**
+ * Access Google Compute Engine metadata
+ */
+public interface GceMetadataService extends LifecycleComponent<GceMetadataService> {
+    /**
+     * <p>Gets metadata on the current running machine (call to
+     * http://metadata.google.internal/computeMetadata/v1/instance/xxx).</p>
+     * <p>For example, you can retrieve network information by replacing xxx with:</p>
+     * <ul>
+     *     <li>`hostname` when we need to resolve the host name</li>
+     *     <li>`network-interfaces/0/ip` when we need to resolve private IP</li>
+     * </ul>
+     * @see org.elasticsearch.cloud.gce.network.GceNameResolver for bindings
+     * @param metadataPath path to metadata information
+     * @return extracted information (for example a hostname or an IP address)
+     * @throws IOException in case metadata URL is not accessible
+     */
+    String metadata(String metadataPath) throws IOException;
+}

plugins/discovery-gce/src/main/java/org/elasticsearch/cloud/gce/GceMetadataServiceImpl.java

@@ -0,0 +1,140 @@
+/*
+ * 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.cloud.gce;
+
+import com.google.api.client.googleapis.javanet.GoogleNetHttpTransport;
+import com.google.api.client.http.GenericUrl;
+import com.google.api.client.http.HttpHeaders;
+import com.google.api.client.http.HttpResponse;
+import com.google.api.client.http.HttpTransport;
+import com.google.api.client.json.JsonFactory;
+import org.elasticsearch.SpecialPermission;
+import org.elasticsearch.cloud.gce.network.GceNameResolver;
+import org.elasticsearch.common.component.AbstractLifecycleComponent;
+import org.elasticsearch.common.inject.Inject;
+import org.elasticsearch.common.network.NetworkService;
+import org.elasticsearch.common.settings.Setting;
+import org.elasticsearch.common.settings.Settings;
+
+import java.io.IOException;
+import java.net.URL;
+import java.security.AccessController;
+import java.security.GeneralSecurityException;
+import java.security.PrivilegedAction;
+import java.security.PrivilegedExceptionAction;
+import java.util.List;
+import java.util.function.Function;
+
+public class GceMetadataServiceImpl extends AbstractLifecycleComponent<GceMetadataService> implements GceMetadataService {
+
+    // Forcing Google Token API URL as set in GCE SDK to
+    //      http://metadata/computeMetadata/v1/instance/service-accounts/default/token
+    // See https://developers.google.com/compute/docs/metadata#metadataserver
+    // all settings just used for testing - not registered by default
+    public static final Setting<String> GCE_HOST =
+        new Setting<>("cloud.gce.host", "http://metadata.google.internal", Function.identity(), Setting.Property.NodeScope);
+
+    /** Global instance of the HTTP transport. */
+    private HttpTransport gceHttpTransport;
+
+    // Forcing Google Token API URL as set in GCE SDK to
+    //      http://metadata/computeMetadata/v1/instance/service-accounts/default/token
+    // See https://developers.google.com/compute/docs/metadata#metadataserver
+    private final String gceHost;
+    private final String metaDataUrl;
+
+    @Inject
+    public GceMetadataServiceImpl(Settings settings, NetworkService networkService) {
+        super(settings);
+        networkService.addCustomNameResolver(new GceNameResolver(settings, this));
+        this.gceHost = GCE_HOST.get(settings);
+        this.metaDataUrl =  gceHost + "/computeMetadata/v1/instance";
+    }
+
+    protected synchronized HttpTransport getGceHttpTransport() throws GeneralSecurityException, IOException {
+        if (gceHttpTransport == null) {
+                gceHttpTransport = GoogleNetHttpTransport.newTrustedTransport();
+            }
+        return gceHttpTransport;
+    }
+
+    @Override
+    public String metadata(String metadataPath) throws IOException {
+        String urlMetadataNetwork = this.metaDataUrl + "/" + metadataPath;
+        logger.debug("get metadata from [{}]", urlMetadataNetwork);
+        final URL url = new URL(urlMetadataNetwork);
+        HttpHeaders headers;
+        try {
+            // hack around code messiness in GCE code
+            // TODO: get this fixed
+            SecurityManager sm = System.getSecurityManager();
+            if (sm != null) {
+                sm.checkPermission(new SpecialPermission());
+            }
+            headers = AccessController.doPrivileged(new PrivilegedExceptionAction<HttpHeaders>() {
+                @Override
+                public HttpHeaders run() throws IOException {
+                    return new HttpHeaders();
+                }
+            });
+            GenericUrl genericUrl = AccessController.doPrivileged(new PrivilegedAction<GenericUrl>() {
+                @Override
+                public GenericUrl run() {
+                    return new GenericUrl(url);
+                }
+            });
+
+            // This is needed to query meta data: https://cloud.google.com/compute/docs/metadata
+            headers.put("Metadata-Flavor", "Google");
+            HttpResponse response;
+            response = getGceHttpTransport().createRequestFactory()
+                .buildGetRequest(genericUrl)
+                .setHeaders(headers)
+                .execute();
+            String metadata = response.parseAsString();
+            logger.debug("metadata found [{}]", metadata);
+            return metadata;
+        } catch (Exception e) {
+            throw new IOException("failed to fetch metadata from [" + urlMetadataNetwork + "]", e);
+        }
+    }
+
+    @Override
+    protected void doStart() {
+
+    }
+
+    @Override
+    protected void doStop() {
+        if (gceHttpTransport != null) {
+            try {
+                gceHttpTransport.shutdown();
+            } catch (IOException e) {
+                logger.warn("unable to shutdown GCE Http Transport", e);
+            }
+            gceHttpTransport = null;
+        }
+    }
+
+    @Override
+    protected void doClose() {
+
+    }
+}

plugins/discovery-gce/src/main/java/org/elasticsearch/cloud/gce/GceModule.java

@@ -20,17 +20,34 @@
 package org.elasticsearch.cloud.gce;
 
 import org.elasticsearch.common.inject.AbstractModule;
+import org.elasticsearch.common.logging.ESLogger;
+import org.elasticsearch.common.logging.Loggers;
+import org.elasticsearch.common.settings.Settings;
 
 public class GceModule extends AbstractModule {
     // pkg private so tests can override with mock
     static Class<? extends GceComputeService> computeServiceImpl = GceComputeServiceImpl.class;
+    static Class<? extends GceMetadataService> metadataServiceImpl = GceMetadataServiceImpl.class;
+
+    protected final Settings settings;
+    protected final ESLogger logger = Loggers.getLogger(GceModule.class);
+
+    public GceModule(Settings settings) {
+        this.settings = settings;
+    }
 
     public static Class<? extends GceComputeService> getComputeServiceImpl() {
         return computeServiceImpl;
     }
 
+    public static Class<? extends GceMetadataService> getMetadataServiceImpl() {
+        return metadataServiceImpl;
+    }
+
     @Override
     protected void configure() {
+        logger.debug("configure GceModule (bind compute and metadata services)");
         bind(GceComputeService.class).to(computeServiceImpl).asEagerSingleton();
+        bind(GceMetadataService.class).to(metadataServiceImpl).asEagerSingleton();
     }
 }

plugins/discovery-gce/src/main/java/org/elasticsearch/cloud/gce/network/GceNameResolver.java

@@ -20,6 +20,7 @@
 package org.elasticsearch.cloud.gce.network;
 
 import org.elasticsearch.cloud.gce.GceComputeService;
+import org.elasticsearch.cloud.gce.GceMetadataService;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.component.AbstractComponent;
 import org.elasticsearch.common.network.NetworkService.CustomNameResolver;
@@ -40,7 +41,7 @@ import java.net.InetAddress;
  */
 public class GceNameResolver extends AbstractComponent implements CustomNameResolver {
 
-    private final GceComputeService gceComputeService;
+    private final GceMetadataService gceMetadataService;
 
     /**
      * enum that can be added to over time with more meta-data types
@@ -72,9 +73,9 @@ public class GceNameResolver extends AbstractComponent implements CustomNameReso
     /**
      * Construct a {@link CustomNameResolver}.
      */
-    public GceNameResolver(Settings settings, GceComputeService gceComputeService) {
+    public GceNameResolver(Settings settings, GceMetadataService gceMetadataService) {
         super(settings);
-        this.gceComputeService = gceComputeService;
+        this.gceMetadataService = gceMetadataService;
     }
 
     /**
@@ -105,7 +106,7 @@ public class GceNameResolver extends AbstractComponent implements CustomNameReso
         }
 
         try {
-            String metadataResult = gceComputeService.metadata(gceMetadataPath);
+            String metadataResult = gceMetadataService.metadata(gceMetadataPath);
             if (metadataResult == null || metadataResult.length() == 0) {
                 throw new IOException("no gce metadata returned from [" + gceMetadataPath + "] for [" + value + "]");
             }

plugins/discovery-gce/src/main/java/org/elasticsearch/plugin/discovery/gce/GceDiscoveryPlugin.java

@@ -37,6 +37,7 @@ import org.elasticsearch.plugins.Plugin;
 
 import java.security.AccessController;
 import java.security.PrivilegedAction;
+import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
 
@@ -85,22 +86,27 @@ public class GceDiscoveryPlugin extends Plugin {
 
     @Override
     public Collection<Module> nodeModules() {
-        return Collections.singletonList(new GceModule());
+        return Collections.singletonList(new GceModule(settings));
     }
 
     @Override
     @SuppressWarnings("rawtypes") // Supertype uses raw type
     public Collection<Class<? extends LifecycleComponent>> nodeServices() {
-        return Collections.singletonList(GceModule.getComputeServiceImpl());
+        logger.debug("Register gce compute and metadata services");
+        Collection<Class<? extends LifecycleComponent>> services = new ArrayList<>();
+        services.add(GceModule.getComputeServiceImpl());
+        services.add(GceModule.getMetadataServiceImpl());
+        return services;
     }
 
     public void onModule(DiscoveryModule discoveryModule) {
+        logger.debug("Register gce discovery type and gce unicast provider");
         discoveryModule.addDiscoveryType(GCE, ZenDiscovery.class);
-        // If discovery.type: gce, we add Gce as a unicast provider
         discoveryModule.addUnicastHostProvider(GCE, GceUnicastHostsProvider.class);
     }
 
     public void onModule(SettingsModule settingsModule) {
+        logger.debug("registering GCE Settings");
         // Register GCE settings
         settingsModule.registerSetting(GceComputeService.PROJECT_SETTING);
         settingsModule.registerSetting(GceComputeService.ZONE_SETTING);

plugins/discovery-gce/src/test/java/org/elasticsearch/discovery/gce/GceComputeServiceMock.java

@@ -45,69 +45,13 @@ public class GceComputeServiceMock extends GceComputeServiceImpl {
 
     protected HttpTransport mockHttpTransport;
 
-    public GceComputeServiceMock(Settings settings, NetworkService networkService) {
+    public GceComputeServiceMock(Settings settings) {
-        super(settings, networkService);
+        super(settings);
-        this.mockHttpTransport = configureMock();
+        this.mockHttpTransport = GceMockUtils.configureMock();
     }
 
     @Override
     protected HttpTransport getGceHttpTransport() throws GeneralSecurityException, IOException {
         return this.mockHttpTransport;
     }
-
-    public static final String GCE_METADATA_URL = "http://metadata.google.internal/computeMetadata/v1/instance";
-
-    protected HttpTransport configureMock() {
-        return new MockHttpTransport() {
-            @Override
-            public LowLevelHttpRequest buildRequest(String method, final String url) throws IOException {
-                return new MockLowLevelHttpRequest() {
-                    @Override
-                    public LowLevelHttpResponse execute() throws IOException {
-                        MockLowLevelHttpResponse response = new MockLowLevelHttpResponse();
-                        response.setStatusCode(200);
-                        response.setContentType(Json.MEDIA_TYPE);
-                        if (url.startsWith(GCE_METADATA_URL)) {
-                            logger.info("--> Simulate GCE Auth/Metadata response for [{}]", url);
-                            response.setContent(readGoogleInternalJsonResponse(url));
-                        } else {
-                            logger.info("--> Simulate GCE API response for [{}]", url);
-                            response.setContent(readGoogleApiJsonResponse(url));
-                        }
-
-                        return response;
-                    }
-                };
-            }
-        };
-    }
-
-    public static String readGoogleInternalJsonResponse(String url) throws IOException {
-        return readJsonResponse(url, "http://metadata.google.internal/");
-    }
-
-    public static String readGoogleApiJsonResponse(String url) throws IOException {
-        return readJsonResponse(url, "https://www.googleapis.com/");
-    }
-
-    private static String readJsonResponse(String url, String urlRoot) throws IOException {
-        // We extract from the url the mock file path we want to use
-        String mockFileName = Strings.replace(url, urlRoot, "");
-
-        URL resource = GceComputeServiceMock.class.getResource(mockFileName);
-        if (resource == null) {
-            throw new IOException("can't read [" + url + "] in src/test/resources/org/elasticsearch/discovery/gce");
-        }
-        try (InputStream is = resource.openStream()) {
-            final StringBuilder sb = new StringBuilder();
-            Streams.readAllLines(is, new Callback<String>() {
-                @Override
-                public void handle(String s) {
-                    sb.append(s);
-                }
-            });
-            String response = sb.toString();
-            return response;
-        }
-    }
 }

plugins/discovery-gce/src/test/java/org/elasticsearch/discovery/gce/GceDiscoverTests.java

@@ -122,7 +122,7 @@ public class GceDiscoverTests extends ESIntegTestCase {
         httpServer = HttpServer.create(new InetSocketAddress(InetAddress.getLoopbackAddress().getHostAddress(), 0), 0);
         httpsServer.setHttpsConfigurator(new HttpsConfigurator(sslContext));
         httpServer.createContext("/computeMetadata/v1/instance/service-accounts/default/token", (s) -> {
-            String response = GceComputeServiceMock.readGoogleInternalJsonResponse(
+            String response = GceMockUtils.readGoogleInternalJsonResponse(
                 "http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/token");
             byte[] responseAsBytes = response.getBytes(StandardCharsets.UTF_8);
             s.sendResponseHeaders(200, responseAsBytes.length);

plugins/discovery-gce/src/test/java/org/elasticsearch/discovery/gce/GceDiscoveryTests.java

@@ -65,7 +65,6 @@ public class GceDiscoveryTests extends ESTestCase {
 
     protected static ThreadPool threadPool;
     protected MockTransportService transportService;
-    protected NetworkService networkService;
     protected GceComputeService mock;
     protected String projectName;
 
@@ -96,11 +95,6 @@ public class GceDiscoveryTests extends ESTestCase {
         transportService = MockTransportService.local(Settings.EMPTY, Version.CURRENT, threadPool);
     }
 
-    @Before
-    public void createNetworkService() {
-        networkService = new NetworkService(Settings.EMPTY);
-    }
-
     @After
     public void stopGceComputeService() {
         if (mock != null) {
@@ -122,7 +116,7 @@ public class GceDiscoveryTests extends ESTestCase {
                 .put(GceComputeService.PROJECT_SETTING.getKey(), projectName)
                 .put(GceComputeService.ZONE_SETTING.getKey(), "europe-west1-b")
                 .build();
-        mock = new GceComputeServiceMock(nodeSettings, networkService);
+        mock = new GceComputeServiceMock(nodeSettings);
         List<DiscoveryNode> discoveryNodes = buildDynamicNodes(mock, nodeSettings);
         assertThat(discoveryNodes, hasSize(2));
     }
@@ -133,7 +127,7 @@ public class GceDiscoveryTests extends ESTestCase {
                 .put(GceComputeService.ZONE_SETTING.getKey(), "europe-west1-b")
                 .putArray(GceUnicastHostsProvider.TAGS_SETTING.getKey(), "elasticsearch")
                 .build();
-        mock = new GceComputeServiceMock(nodeSettings, networkService);
+        mock = new GceComputeServiceMock(nodeSettings);
         List<DiscoveryNode> discoveryNodes = buildDynamicNodes(mock, nodeSettings);
         assertThat(discoveryNodes, hasSize(1));
         assertThat(discoveryNodes.get(0).getId(), is("#cloud-test2-0"));
@@ -145,7 +139,7 @@ public class GceDiscoveryTests extends ESTestCase {
                 .put(GceComputeService.ZONE_SETTING.getKey(), "europe-west1-b")
                 .putArray(GceUnicastHostsProvider.TAGS_SETTING.getKey(), "elasticsearch", "dev")
                 .build();
-        mock = new GceComputeServiceMock(nodeSettings, networkService);
+        mock = new GceComputeServiceMock(nodeSettings);
         List<DiscoveryNode> discoveryNodes = buildDynamicNodes(mock, nodeSettings);
         assertThat(discoveryNodes, hasSize(1));
         assertThat(discoveryNodes.get(0).getId(), is("#cloud-test2-0"));
@@ -156,7 +150,7 @@ public class GceDiscoveryTests extends ESTestCase {
                 .put(GceComputeService.PROJECT_SETTING.getKey(), projectName)
                 .put(GceComputeService.ZONE_SETTING.getKey(), "europe-west1-b")
                 .build();
-        mock = new GceComputeServiceMock(nodeSettings, networkService);
+        mock = new GceComputeServiceMock(nodeSettings);
         List<DiscoveryNode> discoveryNodes = buildDynamicNodes(mock, nodeSettings);
         assertThat(discoveryNodes, hasSize(2));
     }
@@ -167,7 +161,7 @@ public class GceDiscoveryTests extends ESTestCase {
                 .put(GceComputeService.ZONE_SETTING.getKey(), "europe-west1-b")
                 .putArray(GceUnicastHostsProvider.TAGS_SETTING.getKey(), "elasticsearch")
                 .build();
-        mock = new GceComputeServiceMock(nodeSettings, networkService);
+        mock = new GceComputeServiceMock(nodeSettings);
         List<DiscoveryNode> discoveryNodes = buildDynamicNodes(mock, nodeSettings);
         assertThat(discoveryNodes, hasSize(2));
     }
@@ -178,7 +172,7 @@ public class GceDiscoveryTests extends ESTestCase {
                 .put(GceComputeService.ZONE_SETTING.getKey(), "europe-west1-b")
                 .putArray(GceUnicastHostsProvider.TAGS_SETTING.getKey(), "elasticsearch", "dev")
                 .build();
-        mock = new GceComputeServiceMock(nodeSettings, networkService);
+        mock = new GceComputeServiceMock(nodeSettings);
         List<DiscoveryNode> discoveryNodes = buildDynamicNodes(mock, nodeSettings);
         assertThat(discoveryNodes, hasSize(2));
     }
@@ -188,7 +182,7 @@ public class GceDiscoveryTests extends ESTestCase {
                 .put(GceComputeService.PROJECT_SETTING.getKey(), projectName)
                 .putArray(GceComputeService.ZONE_SETTING.getKey(), "us-central1-a", "europe-west1-b")
                 .build();
-        mock = new GceComputeServiceMock(nodeSettings, networkService);
+        mock = new GceComputeServiceMock(nodeSettings);
         List<DiscoveryNode> discoveryNodes = buildDynamicNodes(mock, nodeSettings);
         assertThat(discoveryNodes, hasSize(2));
     }
@@ -198,7 +192,7 @@ public class GceDiscoveryTests extends ESTestCase {
                 .put(GceComputeService.PROJECT_SETTING.getKey(), projectName)
                 .putArray(GceComputeService.ZONE_SETTING.getKey(), "us-central1-a", "europe-west1-b")
                 .build();
-        mock = new GceComputeServiceMock(nodeSettings, networkService);
+        mock = new GceComputeServiceMock(nodeSettings);
         List<DiscoveryNode> discoveryNodes = buildDynamicNodes(mock, nodeSettings);
         assertThat(discoveryNodes, hasSize(2));
     }
@@ -211,14 +205,14 @@ public class GceDiscoveryTests extends ESTestCase {
                 .put(GceComputeService.PROJECT_SETTING.getKey(), projectName)
                 .putArray(GceComputeService.ZONE_SETTING.getKey(), "us-central1-a", "us-central1-b")
                 .build();
-        mock = new GceComputeServiceMock(nodeSettings, networkService);
+        mock = new GceComputeServiceMock(nodeSettings);
         List<DiscoveryNode> discoveryNodes = buildDynamicNodes(mock, nodeSettings);
         assertThat(discoveryNodes, hasSize(0));
     }
 
     public void testIllegalSettingsMissingAllRequired() {
         Settings nodeSettings = Settings.EMPTY;
-        mock = new GceComputeServiceMock(Settings.EMPTY, networkService);
+        mock = new GceComputeServiceMock(nodeSettings);
         try {
             buildDynamicNodes(mock, nodeSettings);
             fail("We expect an IllegalArgumentException for incomplete settings");
@@ -231,7 +225,7 @@ public class GceDiscoveryTests extends ESTestCase {
         Settings nodeSettings = Settings.builder()
             .putArray(GceComputeService.ZONE_SETTING.getKey(), "us-central1-a", "us-central1-b")
             .build();
-        mock = new GceComputeServiceMock(nodeSettings, networkService);
+        mock = new GceComputeServiceMock(nodeSettings);
         try {
             buildDynamicNodes(mock, nodeSettings);
             fail("We expect an IllegalArgumentException for incomplete settings");
@@ -244,7 +238,7 @@ public class GceDiscoveryTests extends ESTestCase {
         Settings nodeSettings = Settings.builder()
             .put(GceComputeService.PROJECT_SETTING.getKey(), projectName)
             .build();
-        mock = new GceComputeServiceMock(nodeSettings, networkService);
+        mock = new GceComputeServiceMock(nodeSettings);
         try {
             buildDynamicNodes(mock, nodeSettings);
             fail("We expect an IllegalArgumentException for incomplete settings");

plugins/discovery-gce/src/test/java/org/elasticsearch/discovery/gce/GceMetadataServiceMock.java

@@ -0,0 +1,47 @@
+/*
+ * 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.gce;
+
+import com.google.api.client.http.HttpTransport;
+import org.elasticsearch.cloud.gce.GceComputeServiceImpl;
+import org.elasticsearch.cloud.gce.GceMetadataServiceImpl;
+import org.elasticsearch.common.network.NetworkService;
+import org.elasticsearch.common.settings.Settings;
+
+import java.io.IOException;
+import java.security.GeneralSecurityException;
+
+/**
+ * Mock for GCE Metadata Service
+ */
+public class GceMetadataServiceMock extends GceMetadataServiceImpl {
+
+    protected HttpTransport mockHttpTransport;
+
+    public GceMetadataServiceMock(Settings settings, NetworkService networkService) {
+        super(settings, networkService);
+        this.mockHttpTransport = GceMockUtils.configureMock();
+    }
+
+    @Override
+    protected HttpTransport getGceHttpTransport() throws GeneralSecurityException, IOException {
+        return this.mockHttpTransport;
+    }
+}

plugins/discovery-gce/src/test/java/org/elasticsearch/discovery/gce/GceMockUtils.java

@@ -0,0 +1,98 @@
+/*
+ * 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.gce;
+
+import com.google.api.client.http.HttpTransport;
+import com.google.api.client.http.LowLevelHttpRequest;
+import com.google.api.client.http.LowLevelHttpResponse;
+import com.google.api.client.json.Json;
+import com.google.api.client.testing.http.MockHttpTransport;
+import com.google.api.client.testing.http.MockLowLevelHttpRequest;
+import com.google.api.client.testing.http.MockLowLevelHttpResponse;
+import org.elasticsearch.cloud.gce.GceMetadataServiceImpl;
+import org.elasticsearch.common.Strings;
+import org.elasticsearch.common.io.Streams;
+import org.elasticsearch.common.logging.ESLogger;
+import org.elasticsearch.common.logging.Loggers;
+import org.elasticsearch.common.util.Callback;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.net.URL;
+
+public class GceMockUtils {
+    protected final static ESLogger logger = Loggers.getLogger(GceMockUtils.class);
+
+    public static final String GCE_METADATA_URL = "http://metadata.google.internal/computeMetadata/v1/instance";
+
+    protected static HttpTransport configureMock() {
+        return new MockHttpTransport() {
+            @Override
+            public LowLevelHttpRequest buildRequest(String method, final String url) throws IOException {
+                return new MockLowLevelHttpRequest() {
+                    @Override
+                    public LowLevelHttpResponse execute() throws IOException {
+                        MockLowLevelHttpResponse response = new MockLowLevelHttpResponse();
+                        response.setStatusCode(200);
+                        response.setContentType(Json.MEDIA_TYPE);
+                        if (url.startsWith(GCE_METADATA_URL)) {
+                            logger.info("--> Simulate GCE Auth/Metadata response for [{}]", url);
+                            response.setContent(readGoogleInternalJsonResponse(url));
+                        } else {
+                            logger.info("--> Simulate GCE API response for [{}]", url);
+                            response.setContent(readGoogleApiJsonResponse(url));
+                        }
+
+                        return response;
+                    }
+                };
+            }
+        };
+    }
+
+    public static String readGoogleInternalJsonResponse(String url) throws IOException {
+        return readJsonResponse(url, "http://metadata.google.internal/");
+    }
+
+    public static String readGoogleApiJsonResponse(String url) throws IOException {
+        return readJsonResponse(url, "https://www.googleapis.com/");
+    }
+
+    private static String readJsonResponse(String url, String urlRoot) throws IOException {
+        // We extract from the url the mock file path we want to use
+        String mockFileName = Strings.replace(url, urlRoot, "");
+
+        URL resource = GceComputeServiceMock.class.getResource(mockFileName);
+        if (resource == null) {
+            throw new IOException("can't read [" + url + "] in src/test/resources/org/elasticsearch/discovery/gce");
+        }
+        try (InputStream is = resource.openStream()) {
+            final StringBuilder sb = new StringBuilder();
+            Streams.readAllLines(is, new Callback<String>() {
+                @Override
+                public void handle(String s) {
+                    sb.append(s);
+                }
+            });
+            String response = sb.toString();
+            return response;
+        }
+    }
+}

plugins/discovery-gce/src/test/java/org/elasticsearch/discovery/gce/GceNetworkTests.java

@@ -104,7 +104,7 @@ public class GceNetworkTests extends ESTestCase {
                 .build();
 
         NetworkService networkService = new NetworkService(nodeSettings);
-        GceComputeServiceMock mock = new GceComputeServiceMock(nodeSettings, networkService);
+        GceMetadataServiceMock mock = new GceMetadataServiceMock(nodeSettings, networkService);
         networkService.addCustomNameResolver(new GceNameResolver(nodeSettings, mock));
         try {
             InetAddress[] addresses = networkService.resolveBindHostAddresses(null);