Request Tracing

Every request needs: a span, RED metrics, and trace context propagation.

Required Attributes

| Attribute | Example | Note | |-----------|---------|------| | http.method | GET, POST | Required | | http.route | /api/orders/:id | Template, not actual path! | | http.status_code | 200, 500 | Required | | user.tier | premium | Recommended (not user_id!) |

RED Metrics

Rate:     http.requests.count{method, route, status}
Errors:   http.requests.errors{method, route, error_type}
Duration: http.request.duration{method, route} (histogram p50/p95/p99)

Middleware Flow

Request → Extract trace context (W3C traceparent)
        → Start span (method + route)
        → Start timer
        → Call handler
        → Set status_code
        → Record duration histogram
        → If 4xx/5xx: increment error counter
        → End span
        → Inject trace context into response

Context Propagation

Critical: Always propagate to downstream services:

// Outgoing request
propagator.inject(ctx, headers)

Common Mistakes

1. Using actual path → /api/orders/12345 creates millions of unique values
2. Missing propagation → Traces break at service boundaries
3. Only tracking success → Must track errors with error_type

References

• references/methodology/red-methodology.md
• references/platforms/{platform}/http.md