feat: allow throttling email sending

Signed-off-by: Heikki Hellgren <heikki.hellgren@op.fi>

plugins/notifications-backend-module-email/config.d.ts

@@ -91,6 +91,10 @@ export interface Config {
          * Concurrency limit for email sending, defaults to 2
          */
         concurrencyLimit?: number;
+        /**
+         * Throttle duration between email sending, defaults to 100ms
+         */
+        throttleInterval?: HumanDuration;
         /**
          * Configuration for broadcast notifications
          */

plugins/notifications-backend-module-email/package.json

@@ -45,7 +45,7 @@
     "@backstage/types": "workspace:^",
     "lodash": "^4.17.21",
     "nodemailer": "^6.9.13",
-    "p-limit": "^3.1.0"
+    "p-throttle": "^6.1.0"
   },
   "devDependencies": {
     "@backstage/backend-test-utils": "workspace:^",

plugins/notifications-backend-module-email/src/processor/NotificationsEmailProcessor.ts

@@ -39,7 +39,7 @@ import { compact } from 'lodash';
 import { DefaultAwsCredentialsManager } from '@backstage/integration-aws-node';
 import { NotificationTemplateRenderer } from '../extensions';
 import Mail from 'nodemailer/lib/mailer';
-import pLimit from 'p-limit';
+import pThrottle from 'p-throttle';
 
 export class NotificationsEmailProcessor implements NotificationProcessor {
   private transporter: any;
@@ -49,6 +49,7 @@ export class NotificationsEmailProcessor implements NotificationProcessor {
   private readonly replyTo?: string;
   private readonly cacheTtl: number;
   private readonly concurrencyLimit: number;
+  private readonly throttleInterval: number;
 
   constructor(
     private readonly logger: LoggerService,
@@ -68,6 +69,11 @@ export class NotificationsEmailProcessor implements NotificationProcessor {
     this.replyTo = emailProcessorConfig.getOptionalString('replyTo');
     this.concurrencyLimit =
       emailProcessorConfig.getOptionalNumber('concurrencyLimit') ?? 2;
+    const throttleConfig =
+      emailProcessorConfig.getOptionalConfig('throttleInterval');
+    this.throttleInterval = throttleConfig
+      ? durationToMilliseconds(readDurationFromConfig(throttleConfig))
+      : 100;
     const cacheConfig = emailProcessorConfig.getOptionalConfig('cache.ttl');
     this.cacheTtl = cacheConfig
       ? durationToMilliseconds(readDurationFromConfig(cacheConfig))
@@ -198,11 +204,14 @@ export class NotificationsEmailProcessor implements NotificationProcessor {
   }
 
   private async sendMails(options: Mail.Options, emails: string[]) {
-    const limit = pLimit(this.concurrencyLimit);
+    const throttle = pThrottle({
+      limit: this.concurrencyLimit,
+      interval: this.throttleInterval,
+    });
+
+    const throttled = throttle((opts: Mail.Options) => this.sendMail(opts));
     await Promise.all(
-      emails.map(email =>
-        limit(() => this.sendMail({ ...options, to: email })),
-      ),
+      emails.map(email => throttled({ ...options, to: email })),
     );
   }
 

yarn.lock

@@ -6051,7 +6051,7 @@ __metadata:
     "@types/nodemailer": ^6.4.14
     lodash: ^4.17.21
     nodemailer: ^6.9.13
-    p-limit: ^3.1.0
+    p-throttle: ^6.1.0
   languageName: unknown
   linkType: soft
 
@@ -33255,6 +33255,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"p-throttle@npm:^6.1.0":
+  version: 6.1.0
+  resolution: "p-throttle@npm:6.1.0"
+  checksum: c1947cca8844564c3d86f8c09067add5e7398b87898cb1f1aea5c48d2c211590d039a316d28a4b0d95364ffa0213c01dff6bf71175c468eab0e381f77715dbdb
+  languageName: node
+  linkType: hard
+
 "p-timeout@npm:^3.2.0":
   version: 3.2.0
   resolution: "p-timeout@npm:3.2.0"