# distributed-tracing — detailed patterns and worked examples

## Distributed Tracing Concepts

### Trace Structure

```
Trace (Request ID: abc123)
  ↓
Span (frontend) [100ms]
  ↓
Span (api-gateway) [80ms]
  ├→ Span (auth-service) [10ms]
  └→ Span (user-service) [60ms]
      └→ Span (database) [40ms]
```

### Key Components

- **Trace** - End-to-end request journey
- **Span** - Single operation within a trace
- **Context** - Metadata propagated between services
- **Tags** - Key-value pairs for filtering
- **Logs** - Timestamped events within a span

## Jaeger Setup

### Kubernetes Deployment

```bash
# Deploy Jaeger Operator
kubectl create namespace observability
kubectl create -f https://github.com/jaegertracing/jaeger-operator/releases/download/v1.51.0/jaeger-operator.yaml -n observability

# Deploy Jaeger instance
kubectl apply -f - <<EOF
apiVersion: jaegertracing.io/v1
kind: Jaeger
metadata:
  name: jaeger
  namespace: observability
spec:
  strategy: production
  storage:
    type: elasticsearch
    options:
      es:
        server-urls: http://elasticsearch:9200
  ingress:
    enabled: true
EOF
```

### Docker Compose

```yaml
version: "3.8"
services:
  jaeger:
    image: jaegertracing/all-in-one:1.62
    ports:
      - "5775:5775/udp"
      - "6831:6831/udp"
      - "6832:6832/udp"
      - "5778:5778"
      - "16686:16686" # UI
      - "14268:14268" # Collector
      - "14250:14250" # gRPC
      - "9411:9411" # Zipkin
    environment:
      - COLLECTOR_ZIPKIN_HOST_PORT=:9411
```

**Reference:** See `references/jaeger-setup.md`

## Application Instrumentation

### OpenTelemetry (Recommended)

#### Python (Flask)

```python
from opentelemetry import trace
from opentelemetry.exporter.jaeger.thrift import JaegerExporter
from opentelemetry.sdk.resources import SERVICE_NAME, Resource
from opentelemetry.sdk.trace import TracerProvider
from opentelemetry.sdk.trace.export import BatchSpanProcessor
from opentelemetry.instrumentation.flask import FlaskInstrumentor
from flask import Flask

# Initialize tracer
resource = Resource(attributes={SERVICE_NAME: "my-service"})
provider = TracerProvider(resource=resource)
processor = BatchSpanProcessor(JaegerExporter(
    agent_host_name="jaeger",
    agent_port=6831,
))
provider.add_span_processor(processor)
trace.set_tracer_provider(provider)

# Instrument Flask
app = Flask(__name__)
FlaskInstrumentor().instrument_app(app)

@app.route('/api/users')
def get_users():
    tracer = trace.get_tracer(__name__)

    with tracer.start_as_current_span("get_users") as span:
        span.set_attribute("user.count", 100)
        # Business logic
        users = fetch_users_from_db()
        return {"users": users}

def fetch_users_from_db():
    tracer = trace.get_tracer(__name__)

    with tracer.start_as_current_span("database_query") as span:
        span.set_attribute("db.system", "postgresql")
        span.set_attribute("db.statement", "SELECT * FROM users")
        # Database query
        return query_database()
```

#### Node.js (Express)

```javascript
const { NodeTracerProvider } = require("@opentelemetry/sdk-trace-node");
const { JaegerExporter } = require("@opentelemetry/exporter-jaeger");
const { BatchSpanProcessor } = require("@opentelemetry/sdk-trace-base");
const { registerInstrumentations } = require("@opentelemetry/instrumentation");
const { HttpInstrumentation } = require("@opentelemetry/instrumentation-http");
const {
  ExpressInstrumentation,
} = require("@opentelemetry/instrumentation-express");

// Initialize tracer
const provider = new NodeTracerProvider({
  resource: { attributes: { "service.name": "my-service" } },
});

const exporter = new JaegerExporter({
  endpoint: "http://jaeger:14268/api/traces",
});

provider.addSpanProcessor(new BatchSpanProcessor(exporter));
provider.register();

// Instrument libraries
registerInstrumentations({
  instrumentations: [new HttpInstrumentation(), new ExpressInstrumentation()],
});

const express = require("express");
const app = express();

app.get("/api/users", async (req, res) => {
  const tracer = trace.getTracer("my-service");
  const span = tracer.startSpan("get_users");

  try {
    const users = await fetchUsers();
    span.setAttributes({ "user.count": users.length });
    res.json({ users });
  } finally {
    span.end();
  }
});
```

#### Go

```go
package main

import (
    "context"
    "go.opentelemetry.io/otel"
    "go.opentelemetry.io/otel/exporters/jaeger"
    "go.opentelemetry.io/otel/sdk/resource"
    sdktrace "go.opentelemetry.io/otel/sdk/trace"
    semconv "go.opentelemetry.io/otel/semconv/v1.4.0"
)

func initTracer() (*sdktrace.TracerProvider, error) {
    exporter, err := jaeger.New(jaeger.WithCollectorEndpoint(
        jaeger.WithEndpoint("http://jaeger:14268/api/traces"),
    ))
    if err != nil {
        return nil, err
    }

    tp := sdktrace.NewTracerProvider(
        sdktrace.WithBatcher(exporter),
        sdktrace.WithResource(resource.NewWithAttributes(
            semconv.SchemaURL,
            semconv.ServiceNameKey.String("my-service"),
        )),
    )

    otel.SetTracerProvider(tp)
    return tp, nil
}

func getUsers(ctx context.Context) ([]User, error) {
    tracer := otel.Tracer("my-service")
    ctx, span := tracer.Start(ctx, "get_users")
    defer span.End()

    span.SetAttributes(attribute.String("user.filter", "active"))

    users, err := fetchUsersFromDB(ctx)
    if err != nil {
        span.RecordError(err)
        return nil, err
    }

    span.SetAttributes(attribute.Int("user.count", len(users)))
    return users, nil
}
```

**Reference:** See `references/instrumentation.md`

## Context Propagation

### HTTP Headers

```
traceparent: 00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01
tracestate: congo=t61rcWkgMzE
```

### Propagation in HTTP Requests

#### Python

```python
from opentelemetry.propagate import inject

headers = {}
inject(headers)  # Injects trace context

response = requests.get('http://downstream-service/api', headers=headers)
```

#### Node.js

```javascript
const { propagation } = require("@opentelemetry/api");

const headers = {};
propagation.inject(context.active(), headers);

axios.get("http://downstream-service/api", { headers });
```

## Tempo Setup (Grafana)

### Kubernetes Deployment

```yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: tempo-config
data:
  tempo.yaml: |
    server:
      http_listen_port: 3200

    distributor:
      receivers:
        jaeger:
          protocols:
            thrift_http:
            grpc:
        otlp:
          protocols:
            http:
            grpc:

    storage:
      trace:
        backend: s3
        s3:
          bucket: tempo-traces
          endpoint: s3.amazonaws.com

    querier:
      frontend_worker:
        frontend_address: tempo-query-frontend:9095
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: tempo
spec:
  replicas: 1
  template:
    spec:
      containers:
        - name: tempo
          image: grafana/tempo:2.7
          args:
            - -config.file=/etc/tempo/tempo.yaml
          volumeMounts:
            - name: config
              mountPath: /etc/tempo
      volumes:
        - name: config
          configMap:
            name: tempo-config
```

**Reference:** See `assets/jaeger-config.yaml.template`

## Sampling Strategies

### Probabilistic Sampling

```yaml
# Sample 1% of traces
sampler:
  type: probabilistic
  param: 0.01
```

### Rate Limiting Sampling

```yaml
# Sample max 100 traces per second
sampler:
  type: ratelimiting
  param: 100
```

### Adaptive Sampling

```python
from opentelemetry.sdk.trace.sampling import ParentBased, TraceIdRatioBased

# Sample based on trace ID (deterministic)
sampler = ParentBased(root=TraceIdRatioBased(0.01))
```

## Trace Analysis

### Finding Slow Requests

**Jaeger Query:**

```
service=my-service
duration > 1s
```

### Finding Errors

**Jaeger Query:**

```
service=my-service
error=true
tags.http.status_code >= 500
```

### Service Dependency Graph

Jaeger automatically generates service dependency graphs showing:

- Service relationships
- Request rates
- Error rates
- Average latencies
