Working example

Signed-off-by: sblausten <sam@roadie.io>

packages/backend/package.json

@@ -40,6 +40,7 @@
     "@backstage/plugin-azure-sites-backend": "workspace:^",
     "@backstage/plugin-badges-backend": "workspace:^",
     "@backstage/plugin-catalog-backend": "workspace:^",
+    "@backstage/plugin-catalog-backend-module-github": "workspace:^",
     "@backstage/plugin-catalog-node": "workspace:^",
     "@backstage/plugin-code-coverage-backend": "workspace:^",
     "@backstage/plugin-entity-feedback-backend": "workspace:^",

packages/backend/src/index.ts

@@ -38,11 +38,10 @@ import {
 import { TaskScheduler } from '@backstage/backend-tasks';
 import { Config } from '@backstage/config';
 import healthcheck from './plugins/healthcheck';
-import { metricsInit, metricsHandler } from './metrics';
+import { metricsHandler, metricsInit } 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 entityFeedback from './plugins/entityFeedback';
 import events from './plugins/events';
@@ -68,6 +67,7 @@ import linguist from './plugins/linguist';
 import { PluginEnvironment } from './types';
 import { ServerPermissionClient } from '@backstage/plugin-permission-node';
 import { DefaultIdentityClient } from '@backstage/plugin-auth-node';
+import createCatalogEventBasedProviders from './plugins/catalogEventBasedProviders';
 
 function makeCreateEnv(config: Config) {
   const root = getRootLogger();
@@ -156,7 +156,7 @@ async function main() {
   const exploreEnv = useHotMemoize(module, () => createEnv('explore'));
   const lighthouseEnv = useHotMemoize(module, () => createEnv('lighthouse'));
 
-  const eventBasedEntityProviders = await catalogEventBasedProviders(
+  const eventBasedEntityProviders = await createCatalogEventBasedProviders(
     catalogEnv,
   );
   const linguistEnv = useHotMemoize(module, () => createEnv('linguist'));

packages/backend/src/plugins/catalog.ts

@@ -21,6 +21,7 @@ import { Router } from 'express';
 import { PluginEnvironment } from '../types';
 import { InMemoryEventBroker } from '@backstage/plugin-events-backend';
 import { GithubEntityProvider } from '@backstage/plugin-catalog-backend-module-github';
+import { ConflictEventSubscriber } from './conflictEventSubscriber';
 
 export default async function createPlugin(
   env: PluginEnvironment,
@@ -40,6 +41,9 @@ export default async function createPlugin(
   builder.addProcessor(new ScaffolderEntitiesProcessor());
   builder.addEntityProvider(providers ?? []);
   const conflictBroker = new InMemoryEventBroker(env.logger);
+  conflictBroker.subscribe(
+    new ConflictEventSubscriber(env.logger, ['conflicts']),
+  );
   builder.setConflictEventBroker(conflictBroker);
   const { processingEngine, router } = await builder.build();
   await processingEngine.start();

packages/backend/src/plugins/conflictEventSubscriber.ts

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2023 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';
+
+export class ConflictEventSubscriber
+  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 ConflictEventSubscriber.name;
+  }
+}

plugins/catalog-backend/src/database/DefaultProcessingDatabase.ts

@@ -359,8 +359,8 @@ export class DefaultProcessingDatabase implements ProcessingDatabase {
           `Detected conflicting entityRef ${entityRef} already referenced by ${conflictingKey} and now also ${locationKey}`,
         );
         if (this.options.conflictEventBroker) {
-          this.options.conflictEventBroker?.publish({
-            topic: 'conflicting-entities',
+          await this.options.conflictEventBroker?.publish({
+            topic: 'conflicts',
             eventPayload: {
               ...entity,
               entityRef,