NestJS Observability

Structured Logging

• Standard: Use nestjs-pino for high-performance JSON logging.
  • Why: Node's built-in console.log is blocking and unstructured.
• Configuration:
  • Redaction: Mandatory masking of sensitive fields (password, token, email).
  • Context: Always inject Logger and set the context (LoginService).

Tracing (Correlation)

• Request ID: Every log line must include a reqId (Request ID).
  • nestjs-pino handles this automatically using AsyncLocalStorage.
  • Propagation: Pass x-request-id to downstream microservices/database queries key to trace flows.

Metrics

• Exposure: Use @willsoto/nestjs-prometheus to expose /metrics for Prometheus scraping.
• Key Metrics:
  1. http_request_duration_seconds (Histogram)
  2. db_query_duration_seconds (Histogram)
  3. memory_usage_bytes (Gauge)

Health Checks

• Terminus: Implement explicit logic for "Liveness" (I'm alive) vs "Readiness" (I can take traffic).
  • DB Check: TypeOrmHealthIndicator / PrismaHealthIndicator.
  • Memory Check: Fail if Heap > 300MB (prevent crash loops).