Lesson 25 — Ultimate: deploy pipeline

Boss level: deploy or roll back

A full deploy pipeline runs stages in order — build, test, deploy, smoke test. If a stage fails, it must roll back: undo the stages that already ran, in reverse order (the last thing done is undone first). [...done].reverse() makes a reversed copy without changing done.

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: this is the core logic of every CI/CD system — and why a failed release leaves production as it was.