Logging, Monitoring & Incident Readiness
Diagnose production failures without leaking user data.
Learning objectives
By the end of this lesson, you should be able to:
- Explain the key concepts and when they are useful.
- Apply the concepts to a realistic engineering scenario.
- Identify common failure modes and choose a practical mitigation.
- Complete the assignment and explain your design decisions.
Core concepts
Production readiness includes structured logs, request IDs, error rates, latency percentiles, dependency health, and actionable alerts. Logs explain individual events; metrics reveal trends; traces connect work across service boundaries. Instrument important user outcomes, not just server uptime.
Worked example
Record event names, request IDs, duration, outcome, and safe identifiers. Redact credentials, authorization headers, payment data, and unnecessary personal information. Alerts should have an owner and a runbook, and should avoid paging on harmless noise.
Engineering principles
- Make assumptions explicit. Document expected inputs, outputs, ownership, and failure behavior.
- Validate at boundaries. Treat user input, files, messages, and third-party responses as untrusted.
- Design for failure. Decide what happens when dependencies time out, data is malformed, or a process is retried.
- Prefer observable behavior. Log meaningful outcomes and expose enough diagnostics to debug without leaking secrets.
- Test the invariant. A test should prove a property that must remain true, not merely repeat the implementation.
Practical assignment
Write a short runbook for elevated API 5xx responses and a database latency spike. Include first checks, rollback criteria, and post-incident follow-up.
Suggested solution and reasoning
Check recent deploys, error distribution, dependency health, and p95 latency; mitigate by rollback or traffic reduction; communicate impact; preserve evidence; then add a regression test and an owner for each follow-up.
Use this as a reference design, not the only possible answer. A strong submission states assumptions, includes failure cases, and demonstrates how correctness will be tested.
Knowledge check
- What problem does this design solve, and what simpler alternative did you consider?
- Which input or dependency is most likely to fail?
- What invariant must remain true after a retry?
- How would you test the unhappy path?
Completion checklist
- I can explain the concepts without reading the lesson.
- I completed the practical assignment.
- I tested at least one failure scenario.
- I documented trade-offs and next steps.