backend: Add support for lifecycle events

Signed-off-by: Johan Haals <johan.haals@gmail.com>

packages/backend-app-api/api-report.md

@@ -4,6 +4,7 @@
 
 ```ts
 import { BackendFeature } from '@backstage/backend-plugin-api';
+import { BackendLifecycle } from '@backstage/backend-plugin-api';
 import { Config } from '@backstage/config';
 import { ExtensionPoint } from '@backstage/backend-plugin-api';
 import { HttpRouterService } from '@backstage/backend-plugin-api';
@@ -66,6 +67,11 @@ export type HttpRouterFactoryOptions = {
   indexPlugin?: string;
 };
 
+// @public (undocumented)
+export const lifecycleFactory: (
+  options?: undefined,
+) => ServiceFactory<BackendLifecycle>;
+
 // @public (undocumented)
 export const loggerFactory: (options?: undefined) => ServiceFactory<Logger>;
 

packages/backend-app-api/src/services/implementations/index.ts

@@ -25,4 +25,5 @@ export { schedulerFactory } from './schedulerService';
 export { tokenManagerFactory } from './tokenManagerService';
 export { urlReaderFactory } from './urlReaderService';
 export { httpRouterFactory } from './httpRouterService';
+export { lifecycleFactory } from './lifecycleService';
 export type { HttpRouterFactoryOptions } from './httpRouterService';

packages/backend-app-api/src/services/implementations/lifecycleService.ts

@@ -0,0 +1,81 @@
+/*
+ * Copyright 2022 The Backstage Authors
+ *
+ * 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.
+ */
+import {
+  BackendLifecycle,
+  createServiceFactory,
+  lifecycleServiceRef,
+  loggerToWinstonLogger,
+  pluginMetadataServiceRef,
+  rootLoggerServiceRef,
+  ShutdownHookOptions,
+} from '@backstage/backend-plugin-api';
+import { Logger } from 'winston';
+
+class BackendLifecycleImpl {
+  constructor(private readonly logger: Logger) {}
+  #shutdownTasks: Array<ShutdownHookOptions & { pluginId: string }> = [];
+
+  addShutdownHook(options: ShutdownHookOptions & { pluginId: string }): void {
+    this.#shutdownTasks.push(options);
+  }
+
+  async shutdown(): Promise<void> {
+    await Promise.all(
+      this.#shutdownTasks.map(hook =>
+        hook
+          .fn()
+          .catch(e => {
+            this.logger.error(
+              `Shutdown hook registered by plugin '${hook.pluginId}' failed with: ${e}`,
+            );
+          })
+          .then(() =>
+            this.logger.debug(
+              `Successfully ran hook registered by plugin ${hook.pluginId}`,
+            ),
+          ),
+      ),
+    );
+  }
+}
+
+class PluginScopedLifecycleImpl implements BackendLifecycle {
+  constructor(
+    private readonly lifecycle: BackendLifecycleImpl,
+    private readonly pluginId: string,
+  ) {}
+  addShutdownHook(options: ShutdownHookOptions): void {
+    this.lifecycle.addShutdownHook({ ...options, pluginId: this.pluginId });
+  }
+}
+
+/** @public */
+export const lifecycleFactory = createServiceFactory({
+  service: lifecycleServiceRef,
+  deps: {
+    logger: rootLoggerServiceRef,
+    plugin: pluginMetadataServiceRef,
+  },
+  async factory({ logger }) {
+    const rootLifecycle = new BackendLifecycleImpl(
+      loggerToWinstonLogger(logger),
+    );
+    process.on('SIGTERM', async () => await rootLifecycle.shutdown());
+    return async ({ plugin }) => {
+      return new PluginScopedLifecycleImpl(rootLifecycle, plugin.getId());
+    };
+  },
+});