Observability Design

Design comprehensive observability across metrics, logs, and traces to understand system behavior and debug issues.

Context

You are building observability for a system. The user struggles to debug production issues or wants better visibility. Read their current monitoring setup.

Domain Context

Based on Google's SRE practices and observability research:

• Metrics: Quantitative measurements (latency, error rate, QPS). Fast queries, low cardinality.
• Logs: Event records with context (error messages, user actions). High volume, searchable.
• Traces: Request flow across services. Shows dependencies and latency breakdown.
• Correlation IDs: Link logs and traces across services. Essential for debugging.
• Cardinality: Unique values for metric labels. High cardinality (millions of unique values) breaks storage.

Instructions

1. Define Key Metrics: For each critical path, specify SLI metrics (success rate, latency, saturation). Example: order checkout: success rate >99.9%, p99 latency <500ms.

2. Design Metrics Collection: Instrument code with metrics (request count, latency histogram, error count). Use metrics library (Prometheus, StatsD). Keep cardinality low.

3. Configure Logging: Log key events (authentication, errors, deployments). Include correlation ID in every log. Aggregate logs centrally (ELK, Datadog).

4. Implement Distributed Tracing: Every request gets trace ID at entry point. Pass to every downstream service. Record span (service name, operation, latency, result).

5. Build Dashboards & Alerts: Dashboard shows health overview (SLI status). Alerts on SLI violation. Alert requires runbook (action to resolve).

Anti-Patterns

• High Cardinality Metrics: Emit metric with user ID as label. Result: millions of unique metrics, breaks storage. Guard: Use low-cardinality labels (service, endpoint); never user ID or request ID.
• Logging Everything: Log every request, every database call. Result: petabytes of data, can't find signal. Guard: Log sparingly; focus on errors and critical paths.
• No Correlation IDs: Cannot trace request across services. Guard: Correlation ID generated at entry point, passed to all downstream services.
• Alerts Without Runbooks: Alert fires but nobody knows what to do. Result: ignored alerts. Guard: Every alert must have clear runbook explaining cause and fix.

Further Reading

• Google's Site Reliability Engineering — observability practices at scale
• The Art of Monitoring by James Turnbull — comprehensive monitoring and alerting strategy
• Observability Engineering by Gundeck and Ligus — modern observability with traces and logs