Circuit Breaker

1. The Incident

It is 2:15 PM on Black Friday. Your checkout page calls a recommendation service to show "customers also bought" items. It is an optional widget. Nobody's purchase depends on it.

At 2:15, the recommendation service's database starts failing. Queries that took 20 ms now take 30 seconds, or never return at all.

Here is the part that surprises people. The recommendation service does not take down recommendations. It takes down checkout.

Why? Run the Timeout lesson's math again