Context Propagation Patterns in Go
Go Concurrency Patterns Series: ← Circuit Breaker | Series Overview | Memory Model → What is Context Propagation? Context propagation is the practice of threading context.Context through your application to carry cancellation signals, deadlines, and request-scoped values across API boundaries, goroutines, and service boundaries. This is critical for building observable, responsive distributed systems. Key Capabilities: Distributed Tracing: Propagate trace IDs across services Cancellation Cascades: Cancel entire request trees Deadline Enforcement: Ensure requests complete within time budgets Request-Scoped Values: Carry metadata without polluting function signatures Real-World Use Cases Microservices: Trace requests across multiple services API Gateways: Propagate timeouts and user context Database Layers: Cancel queries when requests are abandoned Message Queues: Propagate processing deadlines HTTP Middleware: Extract and inject trace headers gRPC Services: Automatic context propagation Basic Context Propagation Propagating Through Function Calls package main import ( "context" "fmt" "time" ) // ServiceA calls ServiceB which calls ServiceC // Context propagates through all layers func ServiceA(ctx context.Context, userID string) error { // Add request-scoped value ctx = context.WithValue(ctx, "user_id", userID) ctx = context.WithValue(ctx, "request_id", generateRequestID()) fmt.Printf("[ServiceA] Processing request for user: %s\n", userID) // Propagate context to next service return ServiceB(ctx) } func ServiceB(ctx context.Context) error { // Retrieve values from context userID := ctx.Value("user_id").(string) requestID := ctx.Value("request_id").(string) fmt.Printf("[ServiceB] User: %s, Request: %s\n", userID, requestID) // Add timeout for downstream call ctx, cancel := context.WithTimeout(ctx, 2*time.Second) defer cancel() return ServiceC(ctx) } func ServiceC(ctx context.Context) error { userID := ctx.Value("user_id").(string) requestID := ctx.Value("request_id").(string) fmt.Printf("[ServiceC] Processing for User: %s, Request: %s\n", userID, requestID) // Simulate work select { case <-time.After(1 * time.Second): fmt.Println("[ServiceC] Work completed") return nil case <-ctx.Done(): fmt.Printf("[ServiceC] Cancelled: %v\n", ctx.Err()) return ctx.Err() } } func generateRequestID() string { return fmt.Sprintf("req-%d", time.Now().UnixNano()) } func main() { ctx := context.Background() err := ServiceA(ctx, "user-123") if err != nil { fmt.Printf("Error: %v\n", err) } } Output: ...