How to test a distributed system?

Conducting testing of a distributed system requires a comprehensive approach that considers the interaction features of components and possible failures.

Main stages:

1. Testing individual services (Unit/Integration Testing):

   • Checking the logic of each microservice in isolation.
   • Testing interaction between individual modules within a single service.

   func TestMyServiceLogic(t *testing.T) {
       // Testing a specific service function
       result := calculateTotal(10, 20)
       if result != 30 {
           t.Errorf("Expected 30, but got %d", result)
       }
   }
   

2. Service integration testing:

   • Checking the correctness of interaction between different services.
   • Using test environments that simulate a real environment.

   // Example of testing HTTP interaction between services
   resp, err := http.Get("http://order-service/api/orders/123")
   // Checking response status and body
   

3. API testing:

   • Testing the public API available to external consumers or other services.
   • Using tools like Postman, Swagger Codegen.

4. Performance and scalability testing:

   • Assessing throughput, delays, and resource usage under load.
   • Using tools like Gatling, JMeter. Checking system behavior under increased load.

5. Fault tolerance and reliability testing (Chaos Engineering):

   • Simulating failures (service shutdowns, network delays, overloads) to test system reactions.
   • Using tools like Chaos Monkey.

   Failure type	Example
   Service shutdown	Stopping a microservice instance
   Network delay	Introducing delay in network packets
   Packet loss	Simulating network packet loss
   High CPU load	Using 100% CPU on the server

6. Security testing:

   • Checking authorization, authentication, protection against common attacks (CSRF, XSS).
   • Using penetration testing.

7. Monitoring and logging:

   • Important for debugging and understanding system behavior in testing and production environments.
   • Using tools like Prometheus, Grafana, ELK Stack.

   // Example of logging in a service
   log.Printf("INFO: Processing order %d", orderID)
   

8. Deployment and configuration testing:

   • Checking the correctness of service deployment and application of configuration files in different environments.

Continuous testing (Continuous Testing) within the CI/CD pipeline is essential, automating the execution of tests at all stages of development.