Introduction

1. What This Module Covers

Every arrow between two boxes in a system diagram is a promise that will sometimes be broken. A call across a network can hang, fail, or half-succeed. It can also succeed so slowly that it is worse than failing.

None of that is unusual. It is the normal operating environment.

The mistake is thinking failures are rare. At scale, rare means constantly.

Run the numbers. At 100,000 orders a day, a failure rate of "only" 1 in 200 is 500 failures every day. Hoping does not solve that.