Add InstanceId configuration in gerrit.config

When Gerrit is setup in a multi-master / multi-site scenario,
the serverId must be the same for all Gerrit masters.
However, it may still be needed to name the different masters
with a configured stable string value, so that it is possible
to identify the different servers across the cluster.

Introduce a new configuration setting called 'gerrit.instanceId'
so that servers can be assigned with a stable-id.

Example of gerrit.config:

[gerrit]
  instanceId = foo-instance-1

The value is optional because it is redundant for single Gerrit
master. The configured instanceId value is injected via the
@GerritInstanceId annotation.

Reference design: https://gerrit-review.googlesource.com/c/homepage/+/263710

Feature: Issue 12684
Change-Id: I9caa4e2faee4c0f8b9cdec8bc661fa0fa3299b91

Documentation/config-gerrit.txt

@@ -2224,6 +2224,12 @@ Path prefix for PolyGerrit's static resources if using a CDN.
 Path for PolyGerrit's favicon after link:#gerrit.canonicalWebUrl[default URL],
 including icon name and extension (.ico should be used).
 
+[[gerrit.instanceId]]gerrit.instanceId::
++
+Optional identifier for this Gerrit instance.
+Used to identify a specific instance within a group of Gerrit instances with the
+same `serverId` (i.e.: a Gerrit cluster).
+Unlike `instanceName` this value is not available in the email templates.
 
 [[gerrit.instanceName]]gerrit.instanceName::
 +

java/com/google/gerrit/acceptance/AbstractDaemonTest.java

@@ -108,6 +108,7 @@ import com.google.gerrit.server.change.RevisionResource;
 import com.google.gerrit.server.config.AllProjectsName;
 import com.google.gerrit.server.config.AllUsersName;
 import com.google.gerrit.server.config.CanonicalWebUrl;
+import com.google.gerrit.server.config.GerritInstanceId;
 import com.google.gerrit.server.config.GerritServerConfig;
 import com.google.gerrit.server.config.PluginConfigFactory;
 import com.google.gerrit.server.config.SitePaths;
@@ -245,6 +246,7 @@ public abstract class AbstractDaemonTest {
   @Inject @CanonicalWebUrl protected Provider<String> canonicalWebUrl;
   @Inject @GerritPersonIdent protected Provider<PersonIdent> serverIdent;
   @Inject @GerritServerConfig protected Config cfg;
+  @Inject @GerritInstanceId @Nullable protected String instanceId;
   @Inject protected AcceptanceTestRequestScope atrScope;
   @Inject protected AccountCache accountCache;
   @Inject protected AccountCreator accountCreator;

java/com/google/gerrit/pgm/Daemon.java

@@ -72,6 +72,7 @@ import com.google.gerrit.server.config.CanonicalWebUrlProvider;
 import com.google.gerrit.server.config.DefaultUrlFormatter;
 import com.google.gerrit.server.config.DownloadConfig;
 import com.google.gerrit.server.config.GerritGlobalModule;
+import com.google.gerrit.server.config.GerritInstanceIdModule;
 import com.google.gerrit.server.config.GerritInstanceNameModule;
 import com.google.gerrit.server.config.GerritOptions;
 import com.google.gerrit.server.config.GerritRuntime;
@@ -446,6 +447,7 @@ public class Daemon extends SiteProgram {
     modules.add(new GpgModule(config));
     modules.add(new StartupChecks.Module());
     modules.add(new GerritInstanceNameModule());
+    modules.add(new GerritInstanceIdModule());
     if (MoreObjects.firstNonNull(httpd, true)) {
       modules.add(
           new CanonicalWebUrlModule() {

java/com/google/gerrit/server/config/GerritInstanceId.java

@@ -0,0 +1,30 @@
+// Copyright (C) 2020 The Android Open Source Project
+//
+// Licensed 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 com.google.gerrit.server.config;
+
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+import com.google.inject.BindingAnnotation;
+import java.lang.annotation.Retention;
+
+/**
+ * Marker on a {@link String} holding the instance id for this server.
+ *
+ * <p>Note that the String may be null, if the administrator has not configured the value. Clients
+ * must handle such cases explicitly.
+ */
+@Retention(RUNTIME)
+@BindingAnnotation
+public @interface GerritInstanceId {}

java/com/google/gerrit/server/config/GerritInstanceIdModule.java

@@ -0,0 +1,30 @@
+// Copyright (C) 2020 The Android Open Source Project
+//
+// Licensed 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 com.google.gerrit.server.config;
+
+import static com.google.inject.Scopes.SINGLETON;
+
+import com.google.inject.AbstractModule;
+
+/** Supports binding the {@link GerritInstanceId} annotation. */
+public class GerritInstanceIdModule extends AbstractModule {
+  @Override
+  protected void configure() {
+    bind(String.class)
+        .annotatedWith(GerritInstanceId.class)
+        .toProvider(GerritInstanceIdProvider.class)
+        .in(SINGLETON);
+  }
+}

java/com/google/gerrit/server/config/GerritInstanceIdProvider.java

@@ -0,0 +1,36 @@
+// Copyright (C) 2020 The Android Open Source Project
+//
+// Licensed 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 com.google.gerrit.server.config;
+
+import com.google.inject.Inject;
+import com.google.inject.Provider;
+import com.google.inject.Singleton;
+import org.eclipse.jgit.lib.Config;
+
+/** Provides {@link GerritInstanceId} from {@code gerrit.instanceId}. */
+@Singleton
+public class GerritInstanceIdProvider implements Provider<String> {
+  private final String instanceId;
+
+  @Inject
+  public GerritInstanceIdProvider(@GerritServerConfig Config cfg) {
+    instanceId = cfg.getString("gerrit", null, "instanceId");
+  }
+
+  @Override
+  public String get() {
+    return instanceId;
+  }
+}

java/com/google/gerrit/testing/InMemoryModule.java

@@ -49,6 +49,7 @@ import com.google.gerrit.server.config.CanonicalWebUrlModule;
 import com.google.gerrit.server.config.CanonicalWebUrlProvider;
 import com.google.gerrit.server.config.DefaultUrlFormatter;
 import com.google.gerrit.server.config.GerritGlobalModule;
+import com.google.gerrit.server.config.GerritInstanceIdModule;
 import com.google.gerrit.server.config.GerritInstanceNameModule;
 import com.google.gerrit.server.config.GerritOptions;
 import com.google.gerrit.server.config.GerritRuntime;
@@ -189,6 +190,7 @@ public class InMemoryModule extends FactoryModule {
     install(new InMemorySchemaModule());
     install(NoSshKeyCache.module());
     install(new GerritInstanceNameModule());
+    install(new GerritInstanceIdModule());
     install(
         new CanonicalWebUrlModule() {
           @Override

javatests/com/google/gerrit/acceptance/config/GerritInstanceIdIT.java

@@ -0,0 +1,34 @@
+// Copyright (C) 2020 The Android Open Source Project
+//
+// Licensed 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 com.google.gerrit.acceptance.config;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.gerrit.acceptance.AbstractDaemonTest;
+import org.junit.Test;
+
+public class GerritInstanceIdIT extends AbstractDaemonTest {
+
+  @Test
+  @GerritConfig(name = "gerrit.instanceId", value = "testInstanceId")
+  public void shouldReturnInstanceIdWhenDefined() {
+    assertThat(instanceId).isEqualTo("testInstanceId");
+  }
+
+  @Test
+  public void shouldReturnNullWhenNotDefined() {
+    assertThat(instanceId).isNull();
+  }
+}