Merge pull request #17953 from backstage/rugvip/startup

backend-app-api: parallelize plugin startup, introduce startup hook and middleware

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

@@ -273,6 +273,10 @@ export interface LifecycleService {
     hook: LifecycleServiceShutdownHook,
     options?: LifecycleServiceShutdownOptions,
   ): void;
+  addStartupHook(
+    hook: LifecycleServiceStartupHook,
+    options?: LifecycleServiceStartupOptions,
+  ): void;
 }
 
 // @public (undocumented)
@@ -283,6 +287,14 @@ export interface LifecycleServiceShutdownOptions {
   logger?: LoggerService;
 }
 
+// @public (undocumented)
+export type LifecycleServiceStartupHook = () => void | Promise<void>;
+
+// @public (undocumented)
+export interface LifecycleServiceStartupOptions {
+  logger?: LoggerService;
+}
+
 // @public
 export interface LoggerService {
   // (undocumented)

packages/backend-plugin-api/src/services/definitions/LifecycleService.ts

@@ -16,6 +16,21 @@
 
 import { LoggerService } from './LoggerService';
 
+/**
+ * @public
+ */
+export type LifecycleServiceStartupHook = () => void | Promise<void>;
+
+/**
+ * @public
+ */
+export interface LifecycleServiceStartupOptions {
+  /**
+   * Optional {@link LoggerService} that will be used for logging instead of the default logger.
+   */
+  logger?: LoggerService;
+}
+
 /**
  * @public
  */
@@ -35,6 +50,20 @@ export interface LifecycleServiceShutdownOptions {
  * @public
  */
 export interface LifecycleService {
+  /**
+   * Register a function to be called when the backend has been initialized.
+   *
+   * @remarks
+   *
+   * When used with plugin scope it will wait for the plugin itself to have been initialized.
+   *
+   * When used with root scope it will wait for all plugins to have been initialized.
+   */
+  addStartupHook(
+    hook: LifecycleServiceStartupHook,
+    options?: LifecycleServiceStartupOptions,
+  ): void;
+
   /**
    * Register a function to be called when the backend is shutting down.
    */

packages/backend-plugin-api/src/services/definitions/index.ts

@@ -26,6 +26,8 @@ export type { DiscoveryService } from './DiscoveryService';
 export type { HttpRouterService } from './HttpRouterService';
 export type {
   LifecycleService,
+  LifecycleServiceStartupHook,
+  LifecycleServiceStartupOptions,
   LifecycleServiceShutdownHook,
   LifecycleServiceShutdownOptions,
 } from './LifecycleService';