# Distributed Tracing Specification

## Overview

Distributed tracing for request tracking across services.

## Distributed Tracing Strategy

**Solution**: OpenTelemetry or Jaeger

**Implementation**:
- Instrument services with tracing
- Propagate trace context
- Collect and store traces
- Visualize in UI

## Trace Sampling

### Sampling Strategy

**Head-Based Sampling**:
- Sample rate: 1% of requests
- Always sample errors
- Always sample slow requests (> 1s)

**Tail-Based Sampling** (optional):
- Sample based on trace characteristics
- More efficient storage

## Trace Correlation Across Services

### Trace Context Propagation

**Headers**: 
- `traceparent` (W3C Trace Context)
- `tracestate` (W3C Trace Context)

**Propagation**: HTTP headers, message queue metadata

### Trace Structure

```
Trace (request)
  ├── Span (API Gateway)
  │   ├── Span (Explorer API)
  │   │   ├── Span (Database Query)
  │   │   └── Span (Cache Lookup)
  │   └── Span (Search Service)
  └── Span (Response)
```

## Performance Analysis Workflows

### Analysis Steps

1. Identify slow requests
2. Trace request path
3. Identify bottlenecks
4. Optimize slow components
5. Verify improvements

## References

- Logging: See `logging.md`
- Metrics: See `metrics-monitoring.md`