Service state and recovery

15-minute session: read for 3 minutes, trace for 3, experiment for 7, and complete the check for 2. Spend longer whenever you need.

A service can be stopped, starting, ready, failed, or restarting. Readiness means it can serve its intended workload, not merely that a PID exists. A restart policy needs backoff and a limit to avoid an endless crash loop. Model startup failure and a dependency becoming available.

Practice and evidence: Predict the example or draw its state transitions. Change one assumption, test the boundary, and record the actual result. Explain what this small model does not establish about a production system.

delays=[min(2**attempt,30) for attempt in range(6)]
print(delays)

Expected result: [1, 2, 4, 8, 16, 30]

Practice and evidence

Keep three notes: your prediction, the actual result, and why they match or differ. The completion check grades understanding; the practice task builds skill.