The Page at 3 a.m. (Incident Response)

The tower that watches every ship in the harbour without boarding one. That board ends when the bell rings. This lesson is what the harbour does next.

Before you start. From The Watchtower (Observability) you need one idea: a pager is an alarm that wakes a person when a number that users feel, like the share of failing requests, goes bad. From The Assembly Line (CI/CD) you need another: a rollback puts the previous version back, the one that was working an hour ago.