feat(events,example): add simple way to add event-based entity providers

Add `DemoEventBasedEntityProvider` as example implementation.

Signed-off-by: Patrick Jungermann <Patrick.Jungermann@gmail.com>

packages/backend/package.json

@@ -39,6 +39,7 @@
     "@backstage/plugin-azure-sites-backend": "workspace:^",
     "@backstage/plugin-badges-backend": "workspace:^",
     "@backstage/plugin-catalog-backend": "workspace:^",
+    "@backstage/plugin-catalog-node": "workspace:^",
     "@backstage/plugin-code-coverage-backend": "workspace:^",
     "@backstage/plugin-events-backend": "workspace:^",
     "@backstage/plugin-events-node": "workspace:^",

packages/backend/src/index.ts

@@ -42,6 +42,7 @@ import { metricsInit, metricsHandler } from './metrics';
 import auth from './plugins/auth';
 import azureDevOps from './plugins/azure-devops';
 import catalog from './plugins/catalog';
+import catalogEventBasedProviders from './plugins/catalogEventBasedProviders';
 import codeCoverage from './plugins/codecoverage';
 import events from './plugins/events';
 import kubernetes from './plugins/kubernetes';
@@ -144,10 +145,17 @@ async function main() {
   const playlistEnv = useHotMemoize(module, () => createEnv('playlist'));
   const eventsEnv = useHotMemoize(module, () => createEnv('events'));
 
+  const eventBasedEntityProviders = await catalogEventBasedProviders(
+    catalogEnv,
+  );
+
   const apiRouter = Router();
-  apiRouter.use('/catalog', await catalog(catalogEnv));
+  apiRouter.use(
+    '/catalog',
+    await catalog(catalogEnv, eventBasedEntityProviders),
+  );
   apiRouter.use('/code-coverage', await codeCoverage(codeCoverageEnv));
-  apiRouter.use('/events', await events(eventsEnv, []));
+  apiRouter.use('/events', await events(eventsEnv, eventBasedEntityProviders));
   apiRouter.use('/rollbar', await rollbar(rollbarEnv));
   apiRouter.use('/scaffolder', await scaffolder(scaffolderEnv));
   apiRouter.use('/tech-insights', await techInsights(techInsightsEnv));

packages/backend/src/plugins/catalog.ts

@@ -15,15 +15,18 @@
  */
 
 import { CatalogBuilder } from '@backstage/plugin-catalog-backend';
+import { EntityProvider } from '@backstage/plugin-catalog-node';
 import { ScaffolderEntitiesProcessor } from '@backstage/plugin-scaffolder-backend';
 import { Router } from 'express';
 import { PluginEnvironment } from '../types';
 
 export default async function createPlugin(
   env: PluginEnvironment,
+  providers?: Array<EntityProvider>,
 ): Promise<Router> {
   const builder = await CatalogBuilder.create(env);
   builder.addProcessor(new ScaffolderEntitiesProcessor());
+  builder.addEntityProvider(providers ?? []);
   const { processingEngine, router } = await builder.build();
   await processingEngine.start();
   return router;

packages/backend/src/plugins/catalogEventBasedProviders.ts

@@ -0,0 +1,61 @@
+/*
+ * Copyright 2020 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 {
+  EntityProvider,
+  EntityProviderConnection,
+} from '@backstage/plugin-catalog-node';
+import { EventParams, EventSubscriber } from '@backstage/plugin-events-node';
+import { Logger } from 'winston';
+import { PluginEnvironment } from '../types';
+
+class DemoEventBasedEntityProvider implements EntityProvider, EventSubscriber {
+  constructor(
+    private readonly logger: Logger,
+    private readonly topics: string[],
+  ) {}
+
+  async onEvent(params: EventParams): Promise<void> {
+    this.logger.info(
+      `onEvent: topic=${params.topic}, metadata=${JSON.stringify(
+        params.metadata,
+      )}, payload=${JSON.stringify(params.eventPayload)}`,
+    );
+  }
+
+  supportsEventTopics(): string[] {
+    return this.topics;
+  }
+
+  async connect(_: EntityProviderConnection): Promise<void> {
+    // not doing anything here
+  }
+
+  getProviderName(): string {
+    return DemoEventBasedEntityProvider.name;
+  }
+}
+
+export default async function createCatalogEventBasedProviders(
+  env: PluginEnvironment,
+): Promise<Array<EntityProvider & EventSubscriber>> {
+  const providers: Array<
+    (EntityProvider & EventSubscriber) | Array<EntityProvider & EventSubscriber>
+  > = [];
+  providers.push(new DemoEventBasedEntityProvider(env.logger, ['example']));
+  // add your event-based entity providers here
+  return providers.flat();
+}

yarn.lock

@@ -22340,6 +22340,7 @@ __metadata:
     "@backstage/plugin-azure-sites-backend": "workspace:^"
     "@backstage/plugin-badges-backend": "workspace:^"
     "@backstage/plugin-catalog-backend": "workspace:^"
+    "@backstage/plugin-catalog-node": "workspace:^"
     "@backstage/plugin-code-coverage-backend": "workspace:^"
     "@backstage/plugin-events-backend": "workspace:^"
     "@backstage/plugin-events-node": "workspace:^"