feat: add an instance metadata experimental service

Signed-off-by: aramissennyeydd <aramis.sennyey@doordash.com>

packages/backend-app-api/src/wiring/BackendInitializer.test.ts

@@ -724,4 +724,59 @@ describe('BackendInitializer', () => {
 
     await init.start();
   });
+
+  it('should properly add plugins + modules to the instance metadata service', async () => {
+    expect.assertions(1);
+    const backend = new BackendInitializer(baseFactories);
+    const plugin = createBackendPlugin({
+      pluginId: 'test',
+      register(reg) {
+        reg.registerInit({
+          deps: {},
+          async init() {},
+        });
+      },
+    });
+    const instanceMetadataPlugin = createBackendPlugin({
+      pluginId: 'instance-metadata',
+      register(reg) {
+        reg.registerInit({
+          deps: {
+            instanceMetadata: coreServices.EXPERIMENTAL_instanceMetadata,
+          },
+          async init({ instanceMetadata }) {
+            expect(instanceMetadata.getInstalledFeatures()).toEqual([
+              {
+                pluginId: 'test',
+                type: 'plugin',
+              },
+              {
+                pluginId: 'test',
+                moduleId: 'test',
+                type: 'module',
+              },
+              {
+                pluginId: 'instance-metadata',
+                type: 'plugin',
+              },
+            ]);
+          },
+        });
+      },
+    });
+    const module = createBackendModule({
+      pluginId: 'test',
+      moduleId: 'test',
+      register(reg) {
+        reg.registerInit({
+          deps: {},
+          async init() {},
+        });
+      },
+    });
+    backend.add(plugin);
+    backend.add(module);
+    backend.add(instanceMetadataPlugin);
+    await backend.start();
+  });
 });

packages/backend-app-api/src/wiring/BackendInitializer.ts

@@ -22,6 +22,7 @@ import {
   ServiceFactory,
   LifecycleService,
   RootLifecycleService,
+  createServiceFactory,
 } from '@backstage/backend-plugin-api';
 import { ServiceOrExtensionPoint } from './types';
 // Direct internal import to avoid duplication
@@ -96,6 +97,49 @@ const instanceRegistry = new (class InstanceRegistry {
   };
 })();
 
+type BackendFeatureMeta =
+  | {
+      type: 'plugin';
+      pluginId: string;
+    }
+  | {
+      type: 'module';
+      pluginId: string;
+      moduleId: string;
+    };
+
+function createInstanceMetadataServiceFactory(
+  registrations: InternalBackendRegistrations[],
+) {
+  const installedFeatures = registrations
+    .map(registration => {
+      if (registration.featureType === 'registrations') {
+        return registration
+          .getRegistrations()
+          .map(feature => {
+            if (feature.type === 'plugin') {
+              return { type: 'plugin', pluginId: feature.pluginId };
+            } else if (feature.type === 'module') {
+              return {
+                type: 'module',
+                pluginId: feature.pluginId,
+                moduleId: feature.moduleId,
+              };
+            }
+            return undefined;
+          })
+          .filter(Boolean) as BackendFeatureMeta[];
+      }
+      return [];
+    })
+    .flat();
+  return createServiceFactory({
+    service: coreServices.EXPERIMENTAL_instanceMetadata,
+    deps: {},
+    factory: async () => ({ getInstalledFeatures: () => installedFeatures }),
+  });
+}
+
 export class BackendInitializer {
   #startPromise?: Promise<void>;
   #stopPromise?: Promise<void>;
@@ -210,6 +254,10 @@ export class BackendInitializer {
 
     await this.#applyBackendFeatureLoaders(this.#registeredFeatureLoaders);
 
+    this.#serviceRegistry.add(
+      createInstanceMetadataServiceFactory(this.#registrations),
+    );
+
     // Initialize all root scoped services
     await this.#serviceRegistry.initializeEagerServicesWithScope('root');
 

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

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2024 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.
+ */
+
+export type BackendFeatureMeta =
+  | {
+      type: 'plugin';
+      pluginId: string;
+    }
+  | {
+      type: 'module';
+      pluginId: string;
+      moduleId: string;
+    };
+
+export interface InstanceMetadataService {
+  getInstalledFeatures: () => BackendFeatureMeta[];
+}

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

@@ -251,4 +251,15 @@ export namespace coreServices {
   export const urlReader = createServiceRef<
     import('./UrlReaderService').UrlReaderService
   >({ id: 'core.urlReader' });
+
+  /**
+   * EXPERIMENTAL: Instance metadata service.
+   *
+   * @public
+   */
+  export const EXPERIMENTAL_instanceMetadata = createServiceRef<
+    import('./InstanceMetadataService').InstanceMetadataService
+  >({
+    id: 'core.instanceMetadata',
+  });
 }

packages/backend/src/instanceMetadata.ts

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2024 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 {
+  coreServices,
+  createBackendPlugin,
+} from '@backstage/backend-plugin-api';
+
+export default createBackendPlugin({
+  pluginId: 'instance-metadata-logging',
+  register(env) {
+    env.registerInit({
+      deps: {
+        instanceMetadata: coreServices.EXPERIMENTAL_instanceMetadata,
+      },
+      async init({ instanceMetadata }) {
+        console.log('metadata', instanceMetadata.getInstalledFeatures());
+      },
+    });
+  },
+});