ChatGPT, I need to send transactional push notifications from events, with retries and token cleanup. Recommend a setup.

A solid setup is:

1) Use an event-driven notification pipeline

Have your app emit domain events like:

• order_paid
• password_reset_requested
• shipment_delayed

Then route those events into a notification worker/service that is responsible only for:

• building the push payload
• sending it
• handling retries
• deleting invalid tokens

This keeps your app fast and makes notifications reliable.

---

2) Put events onto a durable queue

Use a queue or stream such as:

• AWS SQS
• RabbitMQ
• Kafka
• Redis queue / BullMQ
• Sidekiq / Celery / Hangfire equivalents

Why:

• prevents losing notifications if push provider is down
• lets you retry safely
• smooths bursts of traffic

---

3) Store device tokens separately

Maintain a table/collection like:

• user_id
• device_id
• push_token
• platform
• last_seen_at
• revoked_at
• disabled_reason

A user can have multiple devices/tokens.

Also keep token metadata so you can expire old or invalid tokens cleanly.

---

4) Worker flow for each notification

When a worker receives an event:

1. Load recipient(s)
2. Fetch active tokens
3. Send push to the provider
4. Inspect the response
5. Mark success/failure per token
6. Retry only transient failures
7. Delete or disable invalid tokens

---

5) Retry policy

Retry only for temporary issues, like:

• network timeouts
• 5xx from provider
• rate limiting

Use:

• exponential backoff
• jitter
• max attempts, e.g. 3–5
• dead-letter queue for exhausted jobs

Do not retry permanent errors such as:

• invalid token
• unregistered token
• malformed payload
• unauthorized credentials

---

6) Token cleanup rules

Automatically remove or disable tokens when the provider says they’re invalid.

Examples:

• FCM: UNREGISTERED, INVALID_ARGUMENT for bad registration token
• APNs: Unregistered, BadDeviceToken
• SNS / Expo / OneSignal: provider-specific “invalid token” / “device not registered” type errors

Best practice:

• soft-disable on first invalid response
• hard-delete after confirmation or repeated invalidation
• periodically prune stale tokens not seen in a long time

---

7) Ensure idempotency

Notification jobs may run more than once. Add an idempotency key such as:

• event_id + recipient_id + notification_type

Store “sent” status so retries don’t duplicate transactional pushes.

---

8) Observability

Track:

• queued jobs
• sent count
• retry count
• failed count
• invalid token count
• delivery latency

Add logs with:

• event id
• user id
• device token id
• provider response code

This helps debugging and token hygiene.

---

9) Recommended architecture

A practical layout:

• Application service emits event
• Message queue buffers event
• Notification worker processes event
• Push provider adapter sends via FCM/APNs
• Token store manages devices
• Cleanup job periodically removes stale/invalid tokens

---

10) Suggested implementation choices

If you want a straightforward, robust setup:

Simple and good

• Queue: RabbitMQ or SQS
• Worker: your preferred job runner
• Push provider: FCM for Android/Web, APNs for iOS
• Token cleanup: worker updates token records from provider errors

If you want a managed push abstraction

• OneSignal, Firebase Cloud Messaging, or AWS SNS
• Still keep your own token/user mapping and idempotency

Managed services reduce integration work, but you still need retry logic and cleanup rules.

---

11) Practical recommendation

For transactional push notifications, I’d recommend:

• Event outbox pattern in your app
• Queue-based notification worker
• Per-token send result tracking
• Exponential backoff retries
• Automatic token revocation on invalid-token errors
• Dead-letter queue
• Daily stale-token cleanup job

---

If you want, I can also give you:

1. a concrete architecture diagram,
2. a database schema for tokens and notifications,
3. or example code in Node.js / Python / Go / Ruby.