Separate priority lanes. The OTP was still late.

transcript

You gave OTPs their own lane. Their own workers. And the code still arrives late. Why?

Critical lane, bulk lane. Separate topics. Separate worker pools, scaled on their own. But both end at the same provider. And FCM's quota is per project. Not per lane.

600,000 messages a minute. For your whole project. The campaign takes 590,000 of it. The OTP gets a 429. Resource exhausted. Your most urgent message, turned away.

But here's the catch. SMS has the same trap. One sender, one queue. Twilio queues anything over a sender's throughput. An OTP behind a 500,000-text promotion joins the back.

The fix: reserve quota that bulk can never touch. Give OTPs their own SMS sender. And a short validity. Day 2 sets 120 seconds. A stuck code dies instead of arriving stale.

Lanes must reach the provider. A lane that ends at your border isn't really a lane.

Full breakdown in the lecture.