Lesson 23 — Circuit breaker (half-open)

Let the breaker heal itself

An open breaker should not stay open forever. After a cooldown time it goes half-open: it lets one test call through. If that call succeeds, the breaker closes (back to normal); if it fails, it opens again and waits another cooldown.

States: closed → (too many fails) → open → (cooldown passed) → half → closed or open. We pass the time now in so the result is predictable.

Note: real DevOps tools (CI servers, load balancers, Docker, Kubernetes) cannot run in your browser, so this exercise is a small plain-JS simulation of the logic those tools use.

Why it matters: services recover without anyone restarting them by hand at 3 a.m.