Jon Chery
2.1 KiB
2.1 KiB
Logging — Derived Rules
Derives from
domains/observability/first-principles.mdP1 (Structured by Default), P3 (Sufficient Context), P6 (No Secrets in Observability).
Structured by Default (P1)
- Logs are JSON (or structured key-value). Free-form text is for humans; machines need fields.
- Every log entry has:
timestamp,level,message,request_id, plus domain-specific fields. - A log you cannot query is a log you cannot use. Structure is the query API.
Levels (P3 Sufficient Context)
| Level | When |
|---|---|
| ERROR | Something failed; an operator must look |
| WARN | Something unexpected; not a failure but notable |
| INFO | Significant application events (start, stop, deploy, user signup) |
| DEBUG | Diagnostic detail; off in production by default |
- ERROR is not for "this branch ran." ERROR is for "this failed and someone should know."
- Logging everything at ERROR means nothing is an error. Alert fatigue is a defect (observability P7).
Context (P3)
- Every log in a request includes
request_id(correlation ID). Trace the request across services. - Include the user ID, the action, the resource. "What was the user doing?" is answerable.
- A log that says
"failed"with no context is worse than no log. It is noise.
No Secrets (P6, domains/security P9)
- Never log tokens, passwords, API keys, session IDs, PII.
- Redact: replace the secret with
[REDACTED]or a hash. Log the hash, not the value. - Never log the full request body. It may contain a token, a password, or PII.
Volume (P4 Cardinality Discipline, core C8 Economy)
- Don't log every request at INFO. Log significant events.
- A million logs a minute is not "good observability"; it is a storage bill and a signal-to-noise problem.
- Sample high-volume logs (P5 Sampling with Intent). Sample deliberately, not randomly.
What Violates Logging Discipline
| Violation | Principle |
|---|---|
console.log("here") |
P1 (not structured) |
logger.error("done") |
P3 (wrong level) |
logger.info(req.body) |
P6 (secrets), volume |
A log with no request_id |
P3 (no correlation) |
| 10M logs/day at INFO | P4, C8 |