Add an object to store database migration stages (#1170)

* Add an object to store database migration stages

go/registry-3.0-stage-management for more details

This basically boils down to storing an enum in the database so that we
can tell what stage of the migration we're in.

We use a cross-TLD parent so that we can have strong transactional
consistency on retrieval.

core/src/test/java/google/registry/model/common/DatabaseMigrationStateWrapperTest.java

@@ -0,0 +1,111 @@
+// Copyright 2021 The Nomulus Authors. All Rights Reserved.
+//
+// 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 google.registry.model.common;
+
+import static com.google.common.truth.Truth.assertThat;
+import static google.registry.model.common.DatabaseMigrationStateWrapper.MigrationState.DATASTORE_ONLY;
+import static google.registry.model.common.DatabaseMigrationStateWrapper.MigrationState.DATASTORE_PRIMARY;
+import static google.registry.model.common.DatabaseMigrationStateWrapper.MigrationState.DATASTORE_PRIMARY_READ_ONLY;
+import static google.registry.model.common.DatabaseMigrationStateWrapper.MigrationState.SQL_ONLY;
+import static google.registry.model.common.DatabaseMigrationStateWrapper.MigrationState.SQL_PRIMARY;
+import static google.registry.persistence.transaction.TransactionManagerFactory.ofyTm;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import google.registry.model.common.DatabaseMigrationStateWrapper.MigrationState;
+import google.registry.testing.AppEngineExtension;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+public class DatabaseMigrationStateWrapperTest {
+
+  @RegisterExtension
+  public final AppEngineExtension appEngine =
+      AppEngineExtension.builder().withDatastoreAndCloudSql().build();
+
+  @Test
+  void testEmpty_returnsDatastore() {
+    assertThat(DatabaseMigrationStateWrapper.get()).isEqualTo(DATASTORE_ONLY);
+  }
+
+  @Test
+  void testEmpty_canChangeToDatastorePrimary() {
+    DatabaseMigrationStateWrapper.set(DATASTORE_PRIMARY);
+    assertThat(DatabaseMigrationStateWrapper.get()).isEqualTo(DATASTORE_PRIMARY);
+  }
+
+  @Test
+  void testValidTransitions() {
+    runValidTransition(DATASTORE_ONLY, DATASTORE_PRIMARY);
+
+    runValidTransition(DATASTORE_PRIMARY, DATASTORE_ONLY);
+    runValidTransition(DATASTORE_PRIMARY, DATASTORE_PRIMARY_READ_ONLY);
+
+    runValidTransition(DATASTORE_PRIMARY_READ_ONLY, DATASTORE_ONLY);
+    runValidTransition(DATASTORE_PRIMARY_READ_ONLY, DATASTORE_PRIMARY);
+    runValidTransition(DATASTORE_PRIMARY_READ_ONLY, SQL_PRIMARY);
+
+    runValidTransition(SQL_PRIMARY, DATASTORE_PRIMARY_READ_ONLY);
+    runValidTransition(SQL_PRIMARY, SQL_ONLY);
+
+    runValidTransition(SQL_ONLY, SQL_PRIMARY);
+  }
+
+  @Test
+  void testInvalidTransitions() {
+    runInvalidTransition(DATASTORE_ONLY, DATASTORE_ONLY);
+    runInvalidTransition(DATASTORE_ONLY, DATASTORE_PRIMARY_READ_ONLY);
+    runInvalidTransition(DATASTORE_ONLY, SQL_PRIMARY);
+    runInvalidTransition(DATASTORE_ONLY, SQL_ONLY);
+
+    runInvalidTransition(DATASTORE_PRIMARY, DATASTORE_PRIMARY);
+    runInvalidTransition(DATASTORE_PRIMARY, SQL_PRIMARY);
+    runInvalidTransition(DATASTORE_PRIMARY, SQL_ONLY);
+
+    runInvalidTransition(DATASTORE_PRIMARY_READ_ONLY, DATASTORE_PRIMARY_READ_ONLY);
+    runInvalidTransition(DATASTORE_PRIMARY_READ_ONLY, SQL_ONLY);
+
+    runInvalidTransition(SQL_PRIMARY, DATASTORE_ONLY);
+    runInvalidTransition(SQL_PRIMARY, DATASTORE_PRIMARY);
+    runInvalidTransition(SQL_PRIMARY, SQL_PRIMARY);
+
+    runInvalidTransition(SQL_ONLY, DATASTORE_ONLY);
+    runInvalidTransition(SQL_ONLY, DATASTORE_PRIMARY);
+    runInvalidTransition(SQL_ONLY, DATASTORE_PRIMARY_READ_ONLY);
+    runInvalidTransition(SQL_ONLY, SQL_ONLY);
+  }
+
+  private static void runValidTransition(MigrationState from, MigrationState to) {
+    setStateForced(from);
+    DatabaseMigrationStateWrapper.set(to);
+    assertThat(DatabaseMigrationStateWrapper.get()).isEqualTo(to);
+  }
+
+  private static void runInvalidTransition(MigrationState from, MigrationState to) {
+    setStateForced(from);
+    assertThat(
+            assertThrows(
+                IllegalArgumentException.class, () -> DatabaseMigrationStateWrapper.set(to)))
+        .hasMessageThat()
+        .isEqualTo(
+            String.format(
+                "Moving from migration state %s to %s is not a valid transition", from, to));
+  }
+
+  private static void setStateForced(MigrationState migrationState) {
+    DatabaseMigrationStateWrapper wrapper = new DatabaseMigrationStateWrapper(migrationState);
+    ofyTm().transact(() -> ofyTm().put(wrapper));
+    assertThat(DatabaseMigrationStateWrapper.get()).isEqualTo(migrationState);
+  }
+}

core/src/test/resources/google/registry/export/backup_kinds.txt

@@ -2,6 +2,7 @@ AllocationToken
 Cancellation
 ContactResource
 Cursor
+DatabaseMigrationStateWrapper
 DatabaseTransitionSchedule
 DomainBase
 EntityGroupRoot

core/src/test/resources/google/registry/export/crosstld_kinds.txt

@@ -1,6 +1,7 @@
 ClaimsList
 ClaimsListSingleton
 Cursor
+DatabaseMigrationStateWrapper
 DatabaseTransitionSchedule
 KmsSecret
 KmsSecretRevision

core/src/test/resources/google/registry/model/schema.txt

@@ -78,6 +78,18 @@ class google.registry.model.common.Cursor {
   google.registry.model.UpdateAutoTimestamp lastUpdateTime;
   org.joda.time.DateTime cursorTime;
 }
+class google.registry.model.common.DatabaseMigrationStateWrapper {
+  @Id long id;
+  @Parent com.googlecode.objectify.Key<google.registry.model.common.EntityGroupRoot> parent;
+  google.registry.model.common.DatabaseMigrationStateWrapper$MigrationState migrationState;
+}
+enum google.registry.model.common.DatabaseMigrationStateWrapper$MigrationState {
+  DATASTORE_ONLY;
+  DATASTORE_PRIMARY;
+  DATASTORE_PRIMARY_READ_ONLY;
+  SQL_ONLY;
+  SQL_PRIMARY;
+}
 class google.registry.model.common.DatabaseTransitionSchedule {
   @Id java.lang.String transitionId;
   @Parent com.googlecode.objectify.Key<google.registry.model.common.EntityGroupRoot> parent;