2.1.1 Logging
Logs are timestamped events: request id, user, route, status, duration, error. Prefer JSON lines over free-text.
Why it matters
You cannot SSH into every container in production. Logs are how you reconstruct a failure.
How it is used
Log at info for requests and warn/error for failures. Include a correlation / request id. Never log passwords, tokens, or full card numbers. Ship logs to a central store (ELK, Loki, Cloud Logging).