How to Capture gRPC Traffic for Debugging, Testing, and Observability

gRPC (Google Remote Procedure Call) has become a popular framework for high-performance, language-agnostic communication between microservices. It uses HTTP/2 and Protocol Buffers, enabling faster and more efficient service-to-service communication. But with this speed and structure comes complexity—especially when it comes to debugging, testing, and analyzing network calls. Capturing gRPC traffic is crucial for observability, security, performance monitoring, and automated testing. This blog explores various ways to capture gRPC traffic effectively and why it’s important.

Why Capture gRPC Traffic?

Capturing gRPC traffic allows you to:

• Debug issues between client-server interactions.
  
  


• Generate automated test cases based on real-time traffic (e.g., using tools like Keploy).
  
  


• Monitor performance and latency.
  
  


• Detecting anomalies or security threats.
  
  


• Audit service usage and compliance.
  
  

Unlike traditional REST APIs, gRPC traffic is binary, making it harder to inspect using tools like curl or Postman. That’s why special tools and techniques are needed.

 

Methods to Capture gRPC Traffic

1. Using Proxies and Interceptors

a. Envoy Proxy

Envoy is a high-performance proxy that supports gRPC out of the box. By placing Envoy in front of your services, you can log all incoming and outgoing gRPC calls.

• How it works:
  Envoy acts as a sidecar or edge proxy and can be configured with access logs, filters, and tracing tools like Jaeger or Zipkin.
  
  


• Use cases:
  Production traffic analysis, observability, performance monitoring.
  
  


• Bonus:
  You can also export metrics to Prometheus for real-time analytics.
  
  

b. gRPC Interceptors

Interceptors are like middleware for gRPC. You can implement client-side or server-side interceptors to log request and response metadata, payloads, and timing.

// Example in Go

func UnaryLoggingInterceptor(

    ctx context.Context,

    req interface{},

    info *grpc.UnaryServerInfo,

    handler grpc.UnaryHandler,

) (interface{}, error) {

    log.Printf("gRPC Method: %s, Request: %+v", info.FullMethod, req)

    return handler(ctx, req)

}

 

• Use cases:
  Lightweight debugging and local traffic capture.
  
  

2. Using Packet Capture Tools (e.g., Wireshark, tcpdump)

Since gRPC runs on top of HTTP/2, tools like Wireshark can capture raw packets.

• Pros:
  Useful for low-level debugging and reverse engineering.
  
  


• Cons:
  gRPC messages are binary and compressed using Protocol Buffers, so you’ll need the .proto files to decode them.
  
  


• Tips:
  Use Wireshark’s HTTP/2 dissector and load the .proto definitions for better readability.
  
  

3. gRPC-Web for Browser-Based Inspection

If you're using gRPC-Web (common in frontend apps), you can inspect traffic using browser dev tools.

• Use cases:
  Helpful for developers building frontend apps with gRPC-Web and React/Angular.
  
  


• Limitations:
  Only works for gRPC-Web; does not apply to core gRPC in backend microservices.
  
  

4. Using Keploy for Automated Testing

Keploy is an open-source testing tool that captures API (including gRPC) traffic and converts it into test cases.

• How it works:
  Keploy acts as a proxy layer or hooks into your app to intercept gRPC requests/responses and generate mocks and test cases.
  
  


• Advantages:
  
  
  
  
  
  1. Zero manual test writing.
     
     
  
  
  2. Compatible with CI/CD pipelines.
     
     
  
  
  3. Ideal for shift-left testing.
     
     
  
  
  
  


• Example Workflow:
  
  
  
  
  
  1. Run your service with Keploy.
     
     
  
  
  2. Interact with the service.
     
     
  
  
  3. Keploy captures gRPC traffic and generates tests.
     
     
  
  
  4. Replay traffic in isolated test environments.
     
     
  
  
  
  

Best Practices for Capturing gRPC Traffic

• Use logging judiciously: Logging every payload in production may raise performance and security concerns.
  
  


• Mask sensitive data: Always scrub logs for PII or credentials.
  
  


• Integrate with observability tools: Tools like OpenTelemetry can help capture and export gRPC trace data.
  
  


• Automate with CI/CD: Incorporate captured traffic into test pipelines for regression testing.
  
  

Conclusion

Capturing gRPC traffic is essential in modern microservices architecture. Whether you're debugging, testing, or monitoring, understanding the communication between services is key to building resilient and observable systems. While traditional HTTP tools fall short, methods like using proxies (Envoy), interceptors, packet capture tools, and testing frameworks like Keploy can give you deep insight into your gRPC workloads.

By leveraging these techniques, you can ensure more secure, reliable, and testable gRPC applications.

Read more on- https://keploy.io/blog/technology/capture-grpc-traffic-going-out-from-a-server