Logging is one of the three pillars of Observability (Logs, Metrics, Traces).
Today we go deep into how to design logs that are:

• Searchable

• Machine-readable

• Cost-efficient

• Correlated with traces

• Useful during incidents

• Helpful for RCA and SRE workflows

Logs are the most powerful but also the most expensive telemetry signal — so understanding them is critical.

Logging is the process of recording important events happening inside your system.

• Application logs

• System logs

• Access logs

• Security/Audit logs

• Transaction logs

• Cloud platform logs

• Container & Runtime logs

Logs explain why something happened inside your system.

User login failed for John due to invalid token

{
  "event": "login_failed",
  "user": "john",
  "reason": "invalid_token",
  "timestamp": "2025-01-01T12:22:10Z",
  "trace_id": "93ab12f1df",
  "service": "auth-service"
}

• Easy to index

• Easy to parse

• Easy to analyze

• Works with all tools (ELK, Datadog, Splunk, Loki)

• Enables ML-based anomaly detection

Every modern logging architecture uses JSON.

Use correct log levels:

Checkout API returns 502 errors.

payment-service timeout after 5000ms
retrying request...
circuit-breaker OPEN

• Traces → Payment service slow

• Metrics → DB latency high

• Deployment → new version deployed 30 mins ago

Slow external payment gateway → retry storm → DB saturation.

Logs + metrics + traces = instant RCA.

• What is structured logging?

• Why use JSON logs?

• What are log levels?

• How do you enrich logs with trace IDs?

• Explain why indexing affects log costs.

• What is a retention policy?

• Design a logging pipeline for a microservice architecture.

• How do you optimize logs for cost without losing insight?

• What fields should be indexed in an enterprise system?

• Build a multi-cloud logging architecture using OTel + FluentBit + ES + S3.

• Define governance rules for logging across 50+ teams.

• Explain the role of logs in SLOs and SLIs.

What I learned today:
My current logging anti-patterns:
Improvements I will apply:
My retention plan:
Tools I want to test: