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name: Observability & Monitoring description: Structured logging, metrics, distributed tracing, and alerting strategies version: 1.0.0 category: Operations & Reliability agents: [backend-system-architect, code-quality-reviewer, ai-ml-engineer] keywords: [observability, monitoring, logging, metrics, tracing, alerts, Prometheus, OpenTelemetry]

Observability & Monitoring Skill

Comprehensive frameworks for implementing observability including structured logging, metrics, distributed tracing, and alerting.

When to Use

• Setting up application monitoring
• Implementing structured logging
• Adding metrics and dashboards
• Configuring distributed tracing
• Creating alerting rules
• Debugging production issues

Three Pillars of Observability

┌─────────────────┬─────────────────┬─────────────────┐
│     LOGS        │     METRICS     │     TRACES      │
├─────────────────┼─────────────────┼─────────────────┤
│ What happened   │ How is system   │ How do requests │
│ at specific     │ performing      │ flow through    │
│ point in time   │ over time       │ services        │
└─────────────────┴─────────────────┴─────────────────┘

Structured Logging

Log Levels

Level	Use Case
ERROR	Unhandled exceptions, failed operations
WARN	Deprecated API, retry attempts
INFO	Business events, successful operations
DEBUG	Development troubleshooting

Best Practice

// Good: Structured with context
logger.info('User action completed', {
  action: 'purchase',
  userId: user.id,
  orderId: order.id,
  duration_ms: 150
});

// Bad: String interpolation
logger.info(`User ${user.id} completed purchase`);

See templates/structured-logging.ts for Winston setup and request middleware

Metrics Collection

RED Method (Rate, Errors, Duration)

Essential metrics for any service:

• Rate - Requests per second
• Errors - Failed requests per second
• Duration - Request latency distribution

Prometheus Buckets

// HTTP request latency
buckets: [0.01, 0.05, 0.1, 0.5, 1, 2, 5]

// Database query latency
buckets: [0.001, 0.01, 0.05, 0.1, 0.5, 1]

See templates/prometheus-metrics.ts for full metrics configuration

Distributed Tracing

OpenTelemetry Setup

Auto-instrument common libraries:

• Express/HTTP
• PostgreSQL
• Redis

Manual Spans

tracer.startActiveSpan('processOrder', async (span) => {
  span.setAttribute('order.id', orderId);
  // ... work
  span.end();
});

See templates/opentelemetry-tracing.ts for full setup

Alerting Strategy

Severity Levels

Level	Response Time	Examples
Critical (P1)	< 15 min	Service down, data loss
High (P2)	< 1 hour	Major feature broken
Medium (P3)	< 4 hours	Increased error rate
Low (P4)	Next day	Warnings

Key Alerts

Alert	Condition	Severity
ServiceDown	up == 0 for 1m	Critical
HighErrorRate	5xx > 5% for 5m	Critical
HighLatency	p95 > 2s for 5m	High
LowCacheHitRate	< 70% for 10m	Medium

See templates/alerting-rules.yml for Prometheus alerting rules

Health Checks

Kubernetes Probes

Probe	Purpose	Endpoint
Liveness	Is app running?	/health
Readiness	Ready for traffic?	/ready
Startup	Finished starting?	/startup

Readiness Response

{
  "status": "healthy|degraded|unhealthy",
  "checks": {
    "database": { "status": "pass", "latency_ms": 5 },
    "redis": { "status": "pass", "latency_ms": 2 }
  },
  "version": "1.0.0",
  "uptime": 3600
}

See templates/health-checks.ts for implementation

Observability Checklist

Implementation

• JSON structured logging
• Request correlation IDs
• RED metrics (Rate, Errors, Duration)
• Business metrics
• Distributed tracing
• Health check endpoints

Alerting

• Service outage alerts
• Error rate thresholds
• Latency thresholds
• Resource utilization alerts

Dashboards

• Service overview
• Error analysis
• Performance metrics

Extended Thinking Triggers

Use Opus 4.5 extended thinking for:

• Incident investigation - Correlating logs, metrics, traces
• Alert tuning - Reducing noise, catching real issues
• Architecture decisions - Choosing monitoring solutions
• Performance debugging - Cross-service latency analysis

Templates Reference

Template	Purpose
structured-logging.ts	Winston logger with request middleware
prometheus-metrics.ts	HTTP, DB, cache metrics with middleware
opentelemetry-tracing.ts	Distributed tracing setup
alerting-rules.yml	Prometheus alerting rules
health-checks.ts	Liveness, readiness, startup probes