Real-time delivery: one notification platform, five days

Week 6 designs one real system end to end: a notification platform for a fintech super-app in India, with two halves, store and forward through push, SMS and email providers, and a real-time tier that pushes to about 10 million live connections in under a second. The brief and its numbers, why the gateways are sized by connections, how every Week 1 to 5 idea finds a job, one payment notification as you'd say it in an interview, the zombie socket, and the five days ahead.