HBASE-25895 Implement a Cluster Metrics JSON endpoint

Publishes a set of JSON endpoints following a RESTful structure, which expose a subset of the
`o.a.h.h.ClusterMetrics` object tree. The URI structure is as follows

    /api/v1/admin/cluster_metrics
    /api/v1/admin/cluster_metrics/live_servers
    /api/v1/admin/cluster_metrics/dead_servers

Signed-off-by: Sean Busbey <busbey@apache.org>
Signed-off-by: Andrew Purtell <apurtell@apache.org>

hbase-http/src/main/java/org/apache/hadoop/hbase/http/HttpServer.java

@@ -39,6 +39,7 @@ import java.util.stream.Collectors;
 import javax.servlet.Filter;
 import javax.servlet.FilterChain;
 import javax.servlet.FilterConfig;
+import javax.servlet.Servlet;
 import javax.servlet.ServletContext;
 import javax.servlet.ServletException;
 import javax.servlet.ServletRequest;
@@ -838,6 +839,17 @@ public class HttpServer implements FilterContainer {
     addServletWithAuth(name, pathSpec, clazz, false);
   }
 
+  /**
+   * Adds a servlet in the server that any user can access. This method differs from
+   * {@link #addPrivilegedServlet(String, ServletHolder)} in that any authenticated user
+   * can interact with the servlet added by this method.
+   * @param pathSpec The path spec for the servlet
+   * @param holder The servlet holder
+   */
+  public void addUnprivilegedServlet(String pathSpec, ServletHolder holder) {
+    addServletWithAuth(pathSpec, holder, false);
+  }
+
   /**
    * Adds a servlet in the server that only administrators can access. This method differs from
    * {@link #addUnprivilegedServlet(String, String, Class)} in that only those authenticated user
@@ -848,6 +860,16 @@ public class HttpServer implements FilterContainer {
     addServletWithAuth(name, pathSpec, clazz, true);
   }
 
+  /**
+   * Adds a servlet in the server that only administrators can access. This method differs from
+   * {@link #addUnprivilegedServlet(String, ServletHolder)} in that only those
+   * authenticated user who are identified as administrators can interact with the servlet added by
+   * this method.
+   */
+  public void addPrivilegedServlet(String pathSpec, ServletHolder holder) {
+    addServletWithAuth(pathSpec, holder, true);
+  }
+
   /**
    * Internal method to add a servlet to the HTTP server. Developers should not call this method
    * directly, but invoke it via {@link #addUnprivilegedServlet(String, String, Class)} or
@@ -859,6 +881,16 @@ public class HttpServer implements FilterContainer {
     addFilterPathMapping(pathSpec, webAppContext);
   }
 
+  /**
+   * Internal method to add a servlet to the HTTP server. Developers should not call this method
+   * directly, but invoke it via {@link #addUnprivilegedServlet(String, ServletHolder)} or
+   * {@link #addPrivilegedServlet(String, ServletHolder)}.
+   */
+  void addServletWithAuth(String pathSpec, ServletHolder holder, boolean requireAuthz) {
+    addInternalServlet(pathSpec, holder, requireAuthz);
+    addFilterPathMapping(pathSpec, webAppContext);
+  }
+
   /**
    * Add an internal servlet in the server, specifying whether or not to
    * protect with Kerberos authentication.
@@ -867,10 +899,10 @@ public class HttpServer implements FilterContainer {
    * servlets added using this method, filters (except internal Kerberos
    * filters) are not enabled.
    *
-   * @param name The name of the servlet (can be passed as null)
+   * @param name The name of the {@link Servlet} (can be passed as null)
-   * @param pathSpec The path spec for the servlet
+   * @param pathSpec The path spec for the {@link Servlet}
-   * @param clazz The servlet class
+   * @param clazz The {@link Servlet} class
-   * @param requireAuth Require Kerberos authenticate to access servlet
+   * @param requireAuthz Require Kerberos authenticate to access servlet
    */
   void addInternalServlet(String name, String pathSpec,
     Class<? extends HttpServlet> clazz, boolean requireAuthz) {
@@ -878,6 +910,22 @@ public class HttpServer implements FilterContainer {
     if (name != null) {
       holder.setName(name);
     }
+    addInternalServlet(pathSpec, holder, requireAuthz);
+  }
+
+  /**
+   * Add an internal servlet in the server, specifying whether or not to
+   * protect with Kerberos authentication.
+   * Note: This method is to be used for adding servlets that facilitate
+   * internal communication and not for user facing functionality. For
+   * servlets added using this method, filters (except internal Kerberos
+   * filters) are not enabled.
+   *
+   * @param pathSpec The path spec for the {@link Servlet}
+   * @param holder The object providing the {@link Servlet} instance
+   * @param requireAuthz Require Kerberos authenticate to access servlet
+   */
+  void addInternalServlet(String pathSpec, ServletHolder holder, boolean requireAuthz) {
     if (authenticationEnabled && requireAuthz) {
       FilterHolder filter = new FilterHolder(AdminAuthorizedFilter.class);
       filter.setName(AdminAuthorizedFilter.class.getSimpleName());

hbase-http/src/main/java/org/apache/hadoop/hbase/http/InfoServer.java

@@ -1,4 +1,4 @@
-/**
+/*
  * Licensed to the Apache Software Foundation (ASF) under one
  * or more contributor license agreements.  See the NOTICE file
  * distributed with this work for additional information
@@ -19,18 +19,16 @@ package org.apache.hadoop.hbase.http;
 
 import java.io.IOException;
 import java.net.URI;
-
 import javax.servlet.ServletContext;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
-
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.CommonConfigurationKeys;
 import org.apache.hadoop.hbase.HBaseConfiguration;
 import org.apache.hadoop.security.authorize.AccessControlList;
 import org.apache.yetus.audience.InterfaceAudience;
-
 import org.apache.hbase.thirdparty.com.google.common.net.HostAndPort;
+import org.apache.hbase.thirdparty.org.eclipse.jetty.servlet.ServletHolder;
 
 /**
  * Create a Jetty embedded server to answer http requests. The primary goal
@@ -128,6 +126,7 @@ public class InfoServer {
   }
 
   /**
+   * Adds a servlet in the server that any user can access.
    * @see HttpServer#addUnprivilegedServlet(String, String, Class)
    */
   public void addUnprivilegedServlet(String name, String pathSpec,
@@ -136,6 +135,18 @@ public class InfoServer {
   }
 
   /**
+   * Adds a servlet in the server that any user can access.
+   * @see HttpServer#addUnprivilegedServlet(String, ServletHolder)
+   */
+  public void addUnprivilegedServlet(String name, String pathSpec, ServletHolder holder) {
+    if (name != null) {
+      holder.setName(name);
+    }
+    this.httpServer.addUnprivilegedServlet(pathSpec, holder);
+  }
+
+  /**
+   * Adds a servlet in the server that any user can access.
    * @see HttpServer#addPrivilegedServlet(String, String, Class)
    */
   public void addPrivilegedServlet(String name, String pathSpec,

hbase-http/src/main/java/org/apache/hadoop/hbase/http/gson/ByteArraySerializer.java

@@ -0,0 +1,38 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.apache.hadoop.hbase.http.gson;
+
+import java.lang.reflect.Type;
+import org.apache.hadoop.hbase.util.Bytes;
+import org.apache.yetus.audience.InterfaceAudience;
+import org.apache.hbase.thirdparty.com.google.gson.JsonElement;
+import org.apache.hbase.thirdparty.com.google.gson.JsonPrimitive;
+import org.apache.hbase.thirdparty.com.google.gson.JsonSerializationContext;
+import org.apache.hbase.thirdparty.com.google.gson.JsonSerializer;
+
+/**
+ * Serialize a {@code byte[]} using {@link Bytes#toString()}.
+ */
+@InterfaceAudience.Private
+public final class ByteArraySerializer implements JsonSerializer<byte[]> {
+
+  @Override
+  public JsonElement serialize(byte[] src, Type typeOfSrc, JsonSerializationContext context) {
+    return new JsonPrimitive(Bytes.toString(src));
+  }
+}

hbase-http/src/main/java/org/apache/hadoop/hbase/http/gson/GsonMessageBodyWriter.java

@@ -0,0 +1,99 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.apache.hadoop.hbase.http.gson;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.io.OutputStreamWriter;
+import java.io.Writer;
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Type;
+import java.nio.charset.Charset;
+import java.nio.charset.IllegalCharsetNameException;
+import java.nio.charset.StandardCharsets;
+import java.nio.charset.UnsupportedCharsetException;
+import java.util.Optional;
+import javax.inject.Inject;
+import org.apache.yetus.audience.InterfaceAudience;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.apache.hbase.thirdparty.com.google.gson.Gson;
+import org.apache.hbase.thirdparty.javax.ws.rs.Produces;
+import org.apache.hbase.thirdparty.javax.ws.rs.WebApplicationException;
+import org.apache.hbase.thirdparty.javax.ws.rs.core.MediaType;
+import org.apache.hbase.thirdparty.javax.ws.rs.core.MultivaluedMap;
+import org.apache.hbase.thirdparty.javax.ws.rs.ext.MessageBodyWriter;
+
+/**
+ * Implements JSON serialization via {@link Gson} for JAX-RS.
+ */
+@InterfaceAudience.Private
+@Produces(MediaType.APPLICATION_JSON)
+public final class GsonMessageBodyWriter<T> implements MessageBodyWriter<T> {
+  private static final Logger logger = LoggerFactory.getLogger(GsonMessageBodyWriter.class);
+
+  private final Gson gson;
+
+  @Inject
+  public GsonMessageBodyWriter(Gson gson) {
+    this.gson = gson;
+  }
+
+  @Override
+  public boolean isWriteable(Class<?> type, Type genericType, Annotation[] annotations,
+    MediaType mediaType) {
+    return mediaType == null || MediaType.APPLICATION_JSON_TYPE.isCompatible(mediaType);
+  }
+
+  @Override
+  public void writeTo(
+    T t,
+    Class<?> type,
+    Type genericType,
+    Annotation[] annotations,
+    MediaType mediaType,
+    MultivaluedMap<String, Object> httpHeaders,
+    OutputStream entityStream
+  ) throws IOException, WebApplicationException {
+    final Charset outputCharset = requestedCharset(mediaType);
+    try (Writer writer = new OutputStreamWriter(entityStream, outputCharset)) {
+      gson.toJson(t, writer);
+    }
+  }
+
+  private static Charset requestedCharset(MediaType mediaType) {
+    return Optional.ofNullable(mediaType)
+      .map(MediaType::getParameters)
+      .map(params -> params.get("charset"))
+      .map(c -> {
+        try {
+          return Charset.forName(c);
+        } catch (IllegalCharsetNameException e) {
+          logger.debug("Client requested illegal Charset '{}'", c);
+          return null;
+        } catch (UnsupportedCharsetException e) {
+          logger.debug("Client requested unsupported Charset '{}'", c);
+          return null;
+        } catch (Exception e) {
+          logger.debug("Error while resolving Charset '{}'", c, e);
+          return null;
+        }
+      })
+      .orElse(StandardCharsets.UTF_8);
+  }
+}

hbase-http/src/main/java/org/apache/hadoop/hbase/http/jersey/ResponseEntityMapper.java

@@ -0,0 +1,53 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.apache.hadoop.hbase.http.jersey;
+
+import java.io.IOException;
+import org.apache.yetus.audience.InterfaceAudience;
+import org.apache.hbase.thirdparty.com.google.common.collect.ImmutableMap;
+import org.apache.hbase.thirdparty.javax.ws.rs.container.ContainerRequestContext;
+import org.apache.hbase.thirdparty.javax.ws.rs.container.ContainerResponseContext;
+import org.apache.hbase.thirdparty.javax.ws.rs.container.ContainerResponseFilter;
+import org.apache.hbase.thirdparty.javax.ws.rs.core.Response.Status;
+
+/**
+ * Generate a uniform response wrapper around the Entity returned from the resource.
+ * @see <a href="https://jsonapi.org/format/#document-top-level">JSON API Document Structure</a>
+ * @see <a href="https://jsonapi.org/format/#error-objects">JSON API Error Objects</a>
+ */
+@InterfaceAudience.Private
+public class ResponseEntityMapper implements ContainerResponseFilter {
+
+  @Override
+  public void filter(
+    ContainerRequestContext requestContext,
+    ContainerResponseContext responseContext
+  ) throws IOException {
+    /*
+     * Follows very loosely the top-level document specification described in by JSON API. Only
+     * handles 200 response codes; leaves room for errors and other response types.
+     */
+
+    final int statusCode = responseContext.getStatus();
+    if (Status.OK.getStatusCode() != statusCode) {
+      return;
+    }
+
+    responseContext.setEntity(ImmutableMap.of("data", responseContext.getEntity()));
+  }
+}

hbase-http/src/main/java/org/apache/hadoop/hbase/http/jersey/SupplierFactoryAdapter.java

@@ -0,0 +1,42 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.apache.hadoop.hbase.http.jersey;
+
+import java.util.function.Supplier;
+import org.apache.yetus.audience.InterfaceAudience;
+import org.apache.hbase.thirdparty.org.glassfish.hk2.api.Factory;
+
+/**
+ * Use a {@link Supplier} of type {@code T} as a {@link Factory} that provides instances of
+ * {@code T}. Modeled after Jersey's internal implementation.
+ */
+@InterfaceAudience.Private
+public class SupplierFactoryAdapter<T> implements Factory<T> {
+
+  private final Supplier<T> supplier;
+
+  public SupplierFactoryAdapter(Supplier<T> supplier) {
+    this.supplier = supplier;
+  }
+
+  @Override public T provide() {
+    return supplier.get();
+  }
+
+  @Override public void dispose(T instance) { }
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/master/HMaster.java

@@ -131,6 +131,7 @@ import org.apache.hadoop.hbase.master.cleaner.SnapshotCleanerChore;
 import org.apache.hadoop.hbase.master.http.MasterDumpServlet;
 import org.apache.hadoop.hbase.master.http.MasterRedirectServlet;
 import org.apache.hadoop.hbase.master.http.MasterStatusServlet;
+import org.apache.hadoop.hbase.master.http.api_v1.ResourceConfigFactory;
 import org.apache.hadoop.hbase.master.janitor.CatalogJanitor;
 import org.apache.hadoop.hbase.master.locking.LockManager;
 import org.apache.hadoop.hbase.master.migrate.RollingUpgradeChore;
@@ -257,7 +258,8 @@ import org.apache.hbase.thirdparty.org.eclipse.jetty.server.Server;
 import org.apache.hbase.thirdparty.org.eclipse.jetty.server.ServerConnector;
 import org.apache.hbase.thirdparty.org.eclipse.jetty.servlet.ServletHolder;
 import org.apache.hbase.thirdparty.org.eclipse.jetty.webapp.WebAppContext;
-
+import org.apache.hbase.thirdparty.org.glassfish.jersey.server.ResourceConfig;
+import org.apache.hbase.thirdparty.org.glassfish.jersey.servlet.ServletContainer;
 import org.apache.hadoop.hbase.shaded.protobuf.RequestConverter;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.AdminProtos.GetRegionInfoResponse;
 import org.apache.hadoop.hbase.shaded.protobuf.generated.SnapshotProtos.SnapshotDescription;
@@ -281,7 +283,7 @@ public class HMaster extends HBaseServerBase<MasterRpcServices> implements Maste
   private static final Logger LOG = LoggerFactory.getLogger(HMaster.class);
 
   // MASTER is name of the webapp and the attribute name used stuffing this
-  //instance into web context.
+  // instance into a web context !! AND OTHER PLACES !!
   public static final String MASTER = "master";
 
   // Manager and zk listener for master election
@@ -689,9 +691,16 @@ public class HMaster extends HBaseServerBase<MasterRpcServices> implements Maste
   @Override
   protected void configureInfoServer(InfoServer infoServer) {
     infoServer.addUnprivilegedServlet("master-status", "/master-status", MasterStatusServlet.class);
+    infoServer.addUnprivilegedServlet("api_v1", "/api/v1/*", buildApiV1Servlet());
+
     infoServer.setAttribute(MASTER, this);
   }
 
+  private ServletHolder buildApiV1Servlet() {
+    final ResourceConfig config = ResourceConfigFactory.createResourceConfig(conf, this);
+    return new ServletHolder(new ServletContainer(config));
+  }
+
   @Override
   protected Class<? extends HttpServlet> getDumpServlet() {
     return MasterDumpServlet.class;

hbase-server/src/main/java/org/apache/hadoop/hbase/master/http/api_v1/ResourceConfigFactory.java

@@ -0,0 +1,59 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.apache.hadoop.hbase.master.http.api_v1;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hbase.http.jersey.ResponseEntityMapper;
+import org.apache.hadoop.hbase.master.HMaster;
+import org.apache.hadoop.hbase.master.http.gson.GsonSerializationFeature;
+import org.apache.hadoop.hbase.master.http.jersey.MasterFeature;
+import org.apache.yetus.audience.InterfaceAudience;
+import org.apache.hbase.thirdparty.org.glassfish.jersey.server.ResourceConfig;
+import org.apache.hbase.thirdparty.org.glassfish.jersey.server.ServerProperties;
+import org.apache.hbase.thirdparty.org.glassfish.jersey.server.TracingConfig;
+
+/**
+ * Encapsulates construction and configuration of the {@link ResourceConfig} that implements
+ * the {@code cluster-metrics} endpoints.
+ */
+@InterfaceAudience.Private
+public final class ResourceConfigFactory {
+
+  private ResourceConfigFactory() {}
+
+  public static ResourceConfig createResourceConfig(Configuration conf, HMaster master) {
+    return new ResourceConfig()
+      .setApplicationName("api_v1")
+      .packages(ResourceConfigFactory.class.getPackage().getName())
+      // TODO: anything registered here that does not have necessary bindings won't inject properly
+      //   at annotation sites and will result in a WARN logged by o.a.h.t.o.g.j.i.inject.Providers.
+      //   These warnings should be treated by the service as fatal errors, but I have not found a
+      //   callback API for registering a failed binding handler.
+      .register(ResponseEntityMapper.class)
+      .register(GsonSerializationFeature.class)
+      .register(new MasterFeature(master))
+
+      // devs: enable TRACING to see how jersey is dispatching to resources.
+      // in hbase-site.xml, set 'hbase.http.jersey.tracing.type=ON_DEMAND` and
+      // to curl, add `-H X-Jersey-Tracing-Accept:true`
+      .property(ServerProperties.TRACING, conf.get(
+        "hbase.http.jersey.tracing.type", TracingConfig.OFF.name()))
+      .property(ServerProperties.TRACING_THRESHOLD, conf.get(
+        "hbase.http.jersey.tracing.threshold", "TRACE"));
+  }
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/master/http/api_v1/cluster_metrics/model/ClusterMetrics.java

@@ -0,0 +1,70 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.apache.hadoop.hbase.master.http.api_v1.cluster_metrics.model;
+
+import java.util.List;
+import org.apache.hadoop.hbase.ServerName;
+import org.apache.yetus.audience.InterfaceAudience;
+
+/**
+ * Exposes a subset of fields from {@link org.apache.hadoop.hbase.ClusterMetrics}.
+ */
+@InterfaceAudience.Private
+public final class ClusterMetrics {
+
+  private final String hbaseVersion;
+  private final String clusterId;
+  private final ServerName masterName;
+  private final List<ServerName> backupMasterNames;
+
+  public static ClusterMetrics from(org.apache.hadoop.hbase.ClusterMetrics clusterMetrics) {
+    return new ClusterMetrics(
+      clusterMetrics.getHBaseVersion(),
+      clusterMetrics.getClusterId(),
+      clusterMetrics.getMasterName(),
+      clusterMetrics.getBackupMasterNames());
+  }
+
+  private ClusterMetrics(
+    String hbaseVersion,
+    String clusterId,
+    ServerName masterName,
+    List<ServerName> backupMasterNames
+  ) {
+    this.hbaseVersion = hbaseVersion;
+    this.clusterId = clusterId;
+    this.masterName = masterName;
+    this.backupMasterNames = backupMasterNames;
+  }
+
+  public String getHBaseVersion() {
+    return hbaseVersion;
+  }
+
+  public String getClusterId() {
+    return clusterId;
+  }
+
+  public ServerName getMasterName() {
+    return masterName;
+  }
+
+  public List<ServerName> getBackupMasterNames() {
+    return backupMasterNames;
+  }
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/master/http/api_v1/cluster_metrics/package-info.java

@@ -0,0 +1,27 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.
+ */
+
+/**
+ * Exposes the {@link org.apache.hadoop.hbase.ClusterMetrics} object over HTTP as a REST
+ * resource hierarchy. Intended for Master
+ * {@link org.apache.hadoop.hbase.http.InfoServer} consumption only.
+ */
+@InterfaceAudience.Private
+package org.apache.hadoop.hbase.master.http.api_v1.cluster_metrics;
+
+import org.apache.yetus.audience.InterfaceAudience;

hbase-server/src/main/java/org/apache/hadoop/hbase/master/http/api_v1/cluster_metrics/resource/ClusterMetricsResource.java

@@ -0,0 +1,87 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.apache.hadoop.hbase.master.http.api_v1.cluster_metrics.resource;
+
+import java.util.Collection;
+import java.util.EnumSet;
+import java.util.List;
+import java.util.concurrent.ExecutionException;
+import javax.inject.Inject;
+import org.apache.hadoop.hbase.ClusterMetrics.Option;
+import org.apache.hadoop.hbase.ServerMetrics;
+import org.apache.hadoop.hbase.ServerName;
+import org.apache.hadoop.hbase.client.AsyncAdmin;
+import org.apache.hadoop.hbase.master.MasterServices;
+import org.apache.hadoop.hbase.master.http.api_v1.cluster_metrics.model.ClusterMetrics;
+import org.apache.yetus.audience.InterfaceAudience;
+import org.apache.hbase.thirdparty.javax.ws.rs.GET;
+import org.apache.hbase.thirdparty.javax.ws.rs.Path;
+import org.apache.hbase.thirdparty.javax.ws.rs.Produces;
+import org.apache.hbase.thirdparty.javax.ws.rs.core.MediaType;
+
+/**
+ * The root object exposing a subset of {@link org.apache.hadoop.hbase.ClusterMetrics}.
+ */
+@InterfaceAudience.Private
+@Path("cluster_metrics")
+@Produces({ MediaType.APPLICATION_JSON })
+public class ClusterMetricsResource {
+
+  // TODO: using the async client API lends itself well to using the JAX-RS 2.0 Spec's asynchronous
+  //  server APIs. However, these are only available when Jersey is wired up using Servlet 3.x
+  //  container and all of our existing InfoServer stuff is build on Servlet 2.x.
+  //  See also https://blog.allegro.tech/2014/10/async-rest.html#mixing-with-completablefuture
+
+  private final AsyncAdmin admin;
+
+  @Inject
+  public ClusterMetricsResource(MasterServices master) {
+    this.admin = master.getAsyncConnection().getAdmin();
+  }
+
+  private org.apache.hadoop.hbase.ClusterMetrics get(EnumSet<Option> fields)
+    throws ExecutionException, InterruptedException {
+    return admin.getClusterMetrics(fields).get();
+  }
+
+  @GET
+  @Path("/")
+  public ClusterMetrics getBaseMetrics() throws ExecutionException, InterruptedException {
+    final EnumSet<Option> fields = EnumSet.of(
+      Option.HBASE_VERSION,
+      Option.CLUSTER_ID,
+      Option.MASTER,
+      Option.BACKUP_MASTERS
+    );
+    return ClusterMetrics.from(get(fields));
+  }
+
+  @GET
+  @Path("/live_servers")
+  public Collection<ServerMetrics> getLiveServers() throws ExecutionException,
+    InterruptedException {
+    return get(EnumSet.of(Option.LIVE_SERVERS)).getLiveServerMetrics().values();
+  }
+
+  @GET
+  @Path("/dead_servers")
+  public List<ServerName> getDeadServers() throws ExecutionException,
+    InterruptedException {
+    return get(EnumSet.of(Option.DEAD_SERVERS)).getDeadServerNames();
+  }
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/master/http/gson/GsonFactory.java

@@ -0,0 +1,43 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.apache.hadoop.hbase.master.http.gson;
+
+import org.apache.hadoop.hbase.Size;
+import org.apache.hadoop.hbase.http.gson.ByteArraySerializer;
+import org.apache.yetus.audience.InterfaceAudience;
+import org.apache.hbase.thirdparty.com.google.gson.FieldNamingPolicy;
+import org.apache.hbase.thirdparty.com.google.gson.Gson;
+import org.apache.hbase.thirdparty.com.google.gson.GsonBuilder;
+
+/**
+ * Provides a singleton {@link Gson} instance configured just the way we like it.
+ */
+@InterfaceAudience.Private
+public final class GsonFactory {
+
+  private GsonFactory() {}
+
+  public static Gson buildGson() {
+    return new GsonBuilder()
+      .setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
+      .enableComplexMapKeySerialization()
+      .registerTypeAdapter(byte[].class, new ByteArraySerializer())
+      .registerTypeAdapter(Size.class, new SizeAsBytesSerializer())
+      .create();
+  }
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/master/http/gson/GsonSerializationFeature.java

@@ -0,0 +1,67 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.apache.hadoop.hbase.master.http.gson;
+
+import java.util.function.Supplier;
+import javax.inject.Singleton;
+import org.apache.hadoop.hbase.http.gson.GsonMessageBodyWriter;
+import org.apache.hadoop.hbase.http.jersey.SupplierFactoryAdapter;
+import org.apache.yetus.audience.InterfaceAudience;
+import org.apache.hbase.thirdparty.com.google.gson.Gson;
+import org.apache.hbase.thirdparty.javax.ws.rs.core.Feature;
+import org.apache.hbase.thirdparty.javax.ws.rs.core.FeatureContext;
+import org.apache.hbase.thirdparty.javax.ws.rs.ext.MessageBodyWriter;
+import org.apache.hbase.thirdparty.org.glassfish.hk2.utilities.binding.AbstractBinder;
+import org.apache.hbase.thirdparty.org.glassfish.hk2.utilities.binding.ServiceBindingBuilder;
+
+/**
+ * Used to register with (shaded) Jersey the presence of Entity serialization using (shaded) Gson.
+ */
+@InterfaceAudience.Private
+public class GsonSerializationFeature implements Feature {
+
+  @Override
+  public boolean configure(FeatureContext context) {
+    context.register(new Binder());
+    return true;
+  }
+
+  /**
+   * Register this feature's provided functionality and defines their lifetime scopes.
+   */
+  private static class Binder extends AbstractBinder {
+
+    @Override
+    protected void configure() {
+      bindFactory(GsonFactory::buildGson)
+        .to(Gson.class)
+        .in(Singleton.class);
+      bind(GsonMessageBodyWriter.class)
+        .to(MessageBodyWriter.class)
+        .in(Singleton.class);
+    }
+
+    /**
+     * Helper method for smoothing over use of {@link SupplierFactoryAdapter}. Inspired by internal
+     * implementation details of jersey itself.
+     */
+    private <T> ServiceBindingBuilder<T> bindFactory(Supplier<T> supplier) {
+      return bindFactory(new SupplierFactoryAdapter<>(supplier));
+    }
+  }
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/master/http/gson/SizeAsBytesSerializer.java

@@ -0,0 +1,38 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.apache.hadoop.hbase.master.http.gson;
+
+import java.lang.reflect.Type;
+import org.apache.hadoop.hbase.Size;
+import org.apache.yetus.audience.InterfaceAudience;
+import org.apache.hbase.thirdparty.com.google.gson.JsonElement;
+import org.apache.hbase.thirdparty.com.google.gson.JsonPrimitive;
+import org.apache.hbase.thirdparty.com.google.gson.JsonSerializationContext;
+import org.apache.hbase.thirdparty.com.google.gson.JsonSerializer;
+
+/**
+ * Simplify representation of a {@link Size} instance by converting to bytes.
+ */
+@InterfaceAudience.Private
+final class SizeAsBytesSerializer implements JsonSerializer<Size> {
+
+  @Override
+  public JsonElement serialize(Size src, Type typeOfSrc, JsonSerializationContext context) {
+    return new JsonPrimitive(src.get(Size.Unit.BYTE));
+  }
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/master/http/gson/package-info.java

@@ -0,0 +1,24 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.
+ */
+
+/**
+ * This package should be in the hbase-http module as {@code a.a.h.h.http.gson}. It is here instead
+ * because hbase-http does not currently have a dependency on hbase-client, which is required for
+ * implementing {@link org.apache.hadoop.hbase.master.http.gson.SizeAsBytesSerializer}.
+ */
+package org.apache.hadoop.hbase.master.http.gson;

hbase-server/src/main/java/org/apache/hadoop/hbase/master/http/jersey/MasterFeature.java

@@ -0,0 +1,73 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.apache.hadoop.hbase.master.http.jersey;
+
+import java.util.function.Supplier;
+import javax.inject.Singleton;
+import org.apache.hadoop.hbase.http.jersey.SupplierFactoryAdapter;
+import org.apache.hadoop.hbase.master.HMaster;
+import org.apache.hadoop.hbase.master.MasterServices;
+import org.apache.yetus.audience.InterfaceAudience;
+import org.apache.hbase.thirdparty.javax.ws.rs.core.Feature;
+import org.apache.hbase.thirdparty.javax.ws.rs.core.FeatureContext;
+import org.apache.hbase.thirdparty.org.glassfish.hk2.utilities.binding.AbstractBinder;
+import org.apache.hbase.thirdparty.org.glassfish.hk2.utilities.binding.ServiceBindingBuilder;
+
+/**
+ * Implements a Singleton binding to the provided instance of {@link HMaster} for both
+ * {@link HMaster} and {@link MasterServices} injections.
+ */
+@InterfaceAudience.Private
+public class MasterFeature implements Feature {
+
+  private final Supplier<HMaster> supplier;
+
+  public MasterFeature(HMaster master) {
+    this.supplier = () -> master;
+  }
+
+  @Override
+  public boolean configure(FeatureContext context) {
+    context.register(new Binder());
+    return true;
+  }
+
+  /**
+   * Register this feature's provided functionality and defines their lifetime scopes.
+   */
+  private class Binder extends AbstractBinder {
+
+    @Override
+    protected void configure() {
+      bindFactory(supplier)
+        .to(HMaster.class)
+        .in(Singleton.class);
+      bindFactory(supplier)
+        .to(MasterServices.class)
+        .in(Singleton.class);
+    }
+
+    /**
+     * Helper method for smoothing over use of {@link SupplierFactoryAdapter}. Inspired by internal
+     * implementation details of jersey itself.
+     */
+    private <T> ServiceBindingBuilder<T> bindFactory(Supplier<T> supplier) {
+      return bindFactory(new SupplierFactoryAdapter<>(supplier));
+    }
+  }
+}

hbase-server/src/test/java/org/apache/hadoop/hbase/MiniClusterRule.java

@@ -19,6 +19,7 @@ package org.apache.hadoop.hbase;
 
 import java.io.IOException;
 import java.util.concurrent.CompletableFuture;
+import java.util.function.Supplier;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.hbase.client.AsyncConnection;
 import org.apache.hadoop.hbase.client.ConnectionFactory;
@@ -75,6 +76,10 @@ public final class MiniClusterRule extends ExternalResource {
       return this;
     }
 
+    public Builder setConfiguration(Supplier<Configuration> supplier) {
+      return setConfiguration(supplier.get());
+    }
+
     public MiniClusterRule build() {
       return new MiniClusterRule(conf, miniClusterOption != null ? miniClusterOption :
         StartTestingClusterOption.builder().build());

hbase-server/src/test/java/org/apache/hadoop/hbase/master/http/TestApiV1ClusterMetricsResource.java

@@ -0,0 +1,203 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.apache.hadoop.hbase.master.http;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.allOf;
+import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.endsWith;
+import static org.hamcrest.Matchers.startsWith;
+import static org.junit.Assert.assertThrows;
+import java.util.concurrent.CompletableFuture;
+import java.util.function.Supplier;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hbase.ConnectionRule;
+import org.apache.hadoop.hbase.HBaseClassTestRule;
+import org.apache.hadoop.hbase.HConstants;
+import org.apache.hadoop.hbase.MiniClusterRule;
+import org.apache.hadoop.hbase.ServerName;
+import org.apache.hadoop.hbase.StartTestingClusterOption;
+import org.apache.hadoop.hbase.TableName;
+import org.apache.hadoop.hbase.client.AsyncAdmin;
+import org.apache.hadoop.hbase.client.AsyncConnection;
+import org.apache.hadoop.hbase.client.ColumnFamilyDescriptorBuilder;
+import org.apache.hadoop.hbase.client.Durability;
+import org.apache.hadoop.hbase.client.TableDescriptor;
+import org.apache.hadoop.hbase.client.TableDescriptorBuilder;
+import org.apache.hadoop.hbase.master.http.api_v1.cluster_metrics.resource.ClusterMetricsResource;
+import org.apache.hadoop.hbase.testclassification.LargeTests;
+import org.apache.hadoop.hbase.testclassification.MasterTests;
+import org.apache.hadoop.hbase.util.Bytes;
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+import org.junit.rules.ExternalResource;
+import org.junit.rules.RuleChain;
+import org.apache.hbase.thirdparty.javax.ws.rs.NotAcceptableException;
+import org.apache.hbase.thirdparty.javax.ws.rs.client.Client;
+import org.apache.hbase.thirdparty.javax.ws.rs.client.ClientBuilder;
+import org.apache.hbase.thirdparty.javax.ws.rs.client.WebTarget;
+import org.apache.hbase.thirdparty.javax.ws.rs.core.MediaType;
+
+/**
+ * Tests for the master api_v1 {@link ClusterMetricsResource}.
+ */
+@Category({ MasterTests.class, LargeTests.class})
+public class TestApiV1ClusterMetricsResource {
+
+  @ClassRule
+  public static final HBaseClassTestRule CLASS_RULE =
+    HBaseClassTestRule.forClass(TestApiV1ClusterMetricsResource.class);
+
+  private static final MiniClusterRule miniClusterRule = MiniClusterRule.newBuilder()
+    .setMiniClusterOption(StartTestingClusterOption.builder()
+      .numZkServers(3)
+      .numMasters(3)
+      .numDataNodes(3)
+      .build())
+    .setConfiguration(() -> {
+      // enable Master InfoServer and random port selection
+      final Configuration conf = new Configuration();
+      conf.setInt(HConstants.MASTER_INFO_PORT, 0);
+      return conf;
+    })
+    .build();
+  private static final ConnectionRule connectionRule =
+    new ConnectionRule(miniClusterRule::createConnection);
+  private static final ClassSetup classRule = new ClassSetup(connectionRule::getConnection);
+
+  private static final class ClassSetup extends ExternalResource {
+
+    private final Supplier<AsyncConnection> connectionSupplier;
+    private final TableName tableName;
+    private AsyncAdmin admin;
+    private WebTarget target;
+
+    public ClassSetup(final Supplier<AsyncConnection> connectionSupplier) {
+      this.connectionSupplier = connectionSupplier;
+      tableName = TableName.valueOf(TestApiV1ClusterMetricsResource.class.getSimpleName());
+    }
+
+    public WebTarget getTarget() {
+      return target;
+    }
+
+    @Override
+    protected void before() throws Throwable {
+      final AsyncConnection conn = connectionSupplier.get();
+      admin = conn.getAdmin();
+      final TableDescriptor tableDescriptor = TableDescriptorBuilder
+        .newBuilder(tableName)
+        .setColumnFamily(
+          ColumnFamilyDescriptorBuilder.newBuilder(Bytes.toBytes("c")).build())
+        .setDurability(Durability.SKIP_WAL)
+        .build();
+      admin.createTable(tableDescriptor).get();
+
+      final String baseUrl = admin.getMaster()
+        .thenApply(ServerName::getHostname)
+        .thenCombine(
+          admin.getMasterInfoPort(),
+          (hostName, infoPort) -> "http://" + hostName + ":" + infoPort)
+        .get();
+      final Client client = ClientBuilder.newClient();
+      target = client.target(baseUrl).path("api/v1/cluster_metrics");
+    }
+
+    @Override
+    protected void after() {
+      final TableName tableName = TableName.valueOf("test");
+      try {
+        admin.tableExists(tableName)
+          .thenCompose(val -> {
+            if (val) {
+              return admin.disableTable(tableName)
+                .thenCompose(ignored -> admin.deleteTable(tableName));
+            } else {
+              return CompletableFuture.completedFuture(null);
+            }
+          })
+          .get();
+      } catch (Exception e) {
+        throw new RuntimeException(e);
+      }
+    }
+  }
+
+  @ClassRule
+  public static RuleChain ruleChain = RuleChain.outerRule(miniClusterRule)
+    .around(connectionRule)
+    .around(classRule);
+
+  @Test
+  public void testGetRoot() {
+    final String response = classRule.getTarget()
+      .request(MediaType.APPLICATION_JSON_TYPE)
+      .get(String.class);
+    assertThat(response, allOf(
+      containsString("\"hbase_version\":"),
+      containsString("\"cluster_id\":"),
+      containsString("\"master_name\":"),
+      containsString("\"backup_master_names\":")));
+  }
+
+  @Test
+  public void testGetRootHtml() {
+    assertThrows(NotAcceptableException.class, () -> classRule.getTarget()
+      .request(MediaType.TEXT_HTML_TYPE)
+      .get(String.class));
+  }
+
+  @Test
+  public void testGetLiveServers() {
+    final String response = classRule.getTarget()
+      .path("live_servers")
+      .request(MediaType.APPLICATION_JSON_TYPE)
+      .get(String.class);
+    assertThat(response, allOf(
+      startsWith("{\"data\":["),
+      endsWith("]}")));
+  }
+
+  @Test
+  public void testGetLiveServersHtml() {
+    assertThrows(NotAcceptableException.class, () -> classRule.getTarget()
+      .path("live_servers")
+      .request(MediaType.TEXT_HTML_TYPE)
+      .get(String.class));
+  }
+
+  @Test
+  public void testGetDeadServers() {
+    final String response = classRule.getTarget()
+      .path("dead_servers")
+      .request(MediaType.APPLICATION_JSON_TYPE)
+      .get(String.class);
+    assertThat(response, allOf(
+      startsWith("{\"data\":["),
+      endsWith("]}")));
+  }
+
+  @Test
+  public void testGetDeadServersHtml() {
+    assertThrows(NotAcceptableException.class, () -> classRule.getTarget()
+      .path("dead_servers")
+      .request(MediaType.TEXT_HTML_TYPE)
+      .get(String.class));
+  }
+}

hbase-server/src/test/java/org/apache/hadoop/hbase/master/http/gson/GsonFactoryTest.java

@@ -0,0 +1,105 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF 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.apache.hadoop.hbase.master.http.gson;
+
+import static org.junit.Assert.assertEquals;
+import java.util.Map;
+import java.util.TreeMap;
+import org.apache.hadoop.hbase.HBaseClassTestRule;
+import org.apache.hadoop.hbase.Size;
+import org.apache.hadoop.hbase.testclassification.MasterTests;
+import org.apache.hadoop.hbase.testclassification.SmallTests;
+import org.apache.hadoop.hbase.util.Bytes;
+import org.junit.BeforeClass;
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+import org.apache.hbase.thirdparty.com.google.gson.Gson;
+
+@Category({ MasterTests.class, SmallTests.class})
+public class GsonFactoryTest {
+
+  @ClassRule
+  public static final HBaseClassTestRule CLASS_RULE =
+    HBaseClassTestRule.forClass(GsonFactoryTest.class);
+
+  private static Gson gson;
+
+  @BeforeClass
+  public static void beforeClass() {
+    gson = GsonFactory.buildGson();
+  }
+
+  @Test
+  public void testSerializeToLowerCaseUnderscores() {
+    final SomeBean input = new SomeBean(false, 57, "hello\n");
+    final String actual = gson.toJson(input);
+    final String expected = "{\"a_boolean\":false,\"an_int\":57,\"a_string\":\"hello\\n\"}";
+    assertEquals(expected, actual);
+  }
+
+  @Test
+  public void testSerializeMapWithSizeKeys() {
+    final Map<Size, String> input = new TreeMap<>();
+    input.put(new Size(10, Size.Unit.KILOBYTE), "10kb");
+    input.put(new Size(5, Size.Unit.MEGABYTE), "5mb");
+    final String actual = gson.toJson(input);
+    final String expected = "{\"10240.0\":\"10kb\",\"5242880.0\":\"5mb\"}";
+    assertEquals(expected, actual);
+  }
+
+  @Test
+  public void testSerializeNonPrintableByteArrays() {
+    final Map<byte[], byte[]> input = new TreeMap<>(Bytes.BYTES_COMPARATOR);
+    input.put(Bytes.toBytes("this is printable"), new byte[] { 0, 1, 2, 3, 4, 5 });
+    input.put(new byte[] { -127, -63, 0, 63, 127 }, Bytes.toBytes("test"));
+    final String actual = gson.toJson(input);
+    final String expected = "{" +
+      "\"this is printable\":\"\\u0000\\u0001\\u0002\\u0003\\u0004\\u0005\"," +
+      "\"<EFBFBD><EFBFBD>\\u0000?\u007F\":\"test\"}";
+    assertEquals(expected, actual);
+  }
+
+  private static final class SomeBean {
+    private final boolean aBoolean;
+    private final int anInt;
+    private final String aString;
+
+    public SomeBean(
+      final boolean aBoolean,
+      final int anInt,
+      final String aString
+    ) {
+      this.aBoolean = aBoolean;
+      this.anInt = anInt;
+      this.aString = aString;
+    }
+
+    public boolean isaBoolean() {
+      return aBoolean;
+    }
+
+    public int getAnInt() {
+      return anInt;
+    }
+
+    public String getaString() {
+      return aString;
+    }
+  }
+}