Structured Logging Done Right – Best Practices and Interview Guide

Example

{"ts":"2025-03-10T12:00:00Z","level":"INFO","event":"user_login","user_id":"u123","request_id":"r-98","latency_ms":42}

Tip: Always include correlation IDs like request_id or trace_id to connect logs across services.

Want to level up?

• Grokking System Design Fundamentals
• Grokking the System Design Interview
• Grokking Database Fundamentals for Tech Interviews
• Grokking the Coding Interview
• Or practice with Mock Interviews with ex-FAANG engineers

Why Is It Important

• Enables fast filtering, alerting, and visualization
• Reduces MTTR during outages
• Turns logs into metrics for proactive monitoring
• Boosts observability in large-scale systems

Interview Tips

• Define it clearly and mention key fields (timestamp, level, event, service, schema version)
• Talk about redacting PII/secrets
• Highlight log levels, sampling, correlation with traces

Trade-offs

• Pros: consistent schema, automation-friendly, great for monitoring
• Cons: more storage, serialization overhead, strict schema management

Pitfalls

• Free-text logs with no structure
• Missing correlation IDs
• Logging sensitive data
• Using high-cardinality fields (e.g., unique user IDs in metrics)
• Excessive payload sizes and timezone mismatches