feat: add rate limit configuration

Signed-off-by: Kai Dubauskas <kai.dubauskas@doordash.com>

.changeset/pretty-breads-speak.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-notifications-backend-module-slack': patch
+---
+
+The rate limit is now a config variable

plugins/notifications-backend-module-slack/src/lib/SlackNotificationProcessor.test.ts

@@ -953,4 +953,65 @@ describe('SlackNotificationProcessor', () => {
       );
     });
   });
+
+  describe('when rate limit is not configured', () => {
+    it('should use default rate limit of 10 messages per minute', async () => {
+      const slack = new WebClient();
+
+      const processor = SlackNotificationProcessor.fromConfig(config, {
+        auth,
+        logger,
+        catalog: catalogServiceMock({
+          entities: DEFAULT_ENTITIES_RESPONSE.items,
+        }),
+        slack,
+      })[0];
+
+      await processor.processOptions({
+        recipients: { type: 'entity', entityRef: 'group:default/mock' },
+        payload: { title: 'notification' },
+      });
+
+      expect(slack.chat.postMessage).toHaveBeenCalled();
+    });
+  });
+
+  describe('when rate limit is configured', () => {
+    it('should use custom rate limit value', async () => {
+      const slack = new WebClient();
+      const rateLimitConfig = mockServices.rootConfig({
+        data: {
+          app: {
+            baseUrl: 'https://example.org',
+          },
+          notifications: {
+            processors: {
+              slack: [
+                {
+                  token: 'mock-token',
+                  rateLimit: 5,
+                },
+              ],
+            },
+          },
+        },
+      });
+
+      const processor = SlackNotificationProcessor.fromConfig(rateLimitConfig, {
+        auth,
+        logger,
+        catalog: catalogServiceMock({
+          entities: DEFAULT_ENTITIES_RESPONSE.items,
+        }),
+        slack,
+      })[0];
+
+      await processor.processOptions({
+        recipients: { type: 'entity', entityRef: 'group:default/mock' },
+        payload: { title: 'notification' },
+      });
+
+      expect(slack.chat.postMessage).toHaveBeenCalled();
+    });
+  });
 });

plugins/notifications-backend-module-slack/src/lib/SlackNotificationProcessor.ts

@@ -68,10 +68,12 @@ export class SlackNotificationProcessor implements NotificationProcessor {
       const slack = options.slack ?? new WebClient(token);
       const broadcastChannels = c.getOptionalStringArray('broadcastChannels');
       const username = c.getOptionalString('username');
+      const rateLimit = c.getOptionalNumber('rateLimit');
       return new SlackNotificationProcessor({
         slack,
         broadcastChannels,
         username,
+        rateLimit,
         ...options,
       });
     });
@@ -84,9 +86,17 @@ export class SlackNotificationProcessor implements NotificationProcessor {
     catalog: CatalogService;
     broadcastChannels?: string[];
     username?: string;
+    rateLimit?: number;
   }) {
-    const { auth, catalog, logger, slack, broadcastChannels, username } =
-      options;
+    const {
+      auth,
+      catalog,
+      logger,
+      slack,
+      broadcastChannels,
+      username,
+      rateLimit,
+    } = options;
     this.logger = logger;
     this.catalog = catalog;
     this.auth = auth;
@@ -134,7 +144,7 @@ export class SlackNotificationProcessor implements NotificationProcessor {
     );
 
     const throttle = pThrottle({
-      limit: 10,
+      limit: rateLimit ?? 10,
       interval: durationToMilliseconds({ minutes: 1 }),
     });
     const throttled = throttle((opts: ChatPostMessageArguments) =>