Understand These 5 Microservices Questions for Interviews

We will discuss some critical interview questions related to Microservices.

1. How Do Microservices Communicate With Each Other?

Microservices can communicate with each other using either:

• Synchronous protocols like HTTP/REST
• Asynchronous protocols like RabbitMQ, Kafka

Communication Type	Description	Example Tools	Protocol
Synchronous	Real-time, blocking	REST, gRPC, Feign	HTTP, gRPC
Asynchronous	Event-driven, non-blocking	Kafka, RabbitMQ	AMQP, Kafka

So what are the differences between them?

Feature	REST (Synchronous)	Messaging (Asynchronous)
Timing	Real-time	Delayed, eventually consistent
Coupling	Tightly coupled	Loosely coupled
Failure handling	Retry logic or circuit breaker	Message retries, dead letter queues
Tools	Feign, RestTemplate	Kafka, RabbitMQ

Rest Template Examples

@Service
public class ProductClient {
    private final RestTemplate restTemplate = new RestTemplate();

    public String getProductById(Long productId) {
        String url = "http://localhost:8081/products/" + productId;
        return restTemplate.getForObject(url, String.class);
    }
}

Using Feign Client

@FeignClient(name = "product-service")
public interface ProductClient {

    @GetMapping("/products/{id}")
    String getProduct(@PathVariable("id") Long id);
}

2. How Can You Secure Microservices?

We can use OAuth2, JWT or API Keys to secure microservices.

JWT Example

@EnableWebSecurity
public class SecurityConfig {

    @Bean
    public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
        http
          .authorizeHttpRequests(auth -> auth
              .requestMatchers("/admin/**").hasRole("ADMIN")
              .anyRequest().authenticated())
          .oauth2ResourceServer(oauth2 -> oauth2.jwt());
        return http.build();
    }
}

3. What Are the Key Differences Between Monolithic and Microservices Architectures?

Feature	Monolithic Architecture	Microservices Architecture
Codebase	Single unified codebase	Multiple small, independent codebases
Deployment	Entire application deployed at once	Each service can be deployed independently
Scalability	Hard to scale specific features	Easy to scale individual services
Technology Stack	Typically a single tech stack	Can use different stacks per service
Fault Isolation	One failure can crash the entire app	Failures isolated to individual services

4. What Are the Common Microservices Patterns?

Pattern	Purpose	Example Library
API Gateway	Entry point for requests	Spring Cloud Gateway
Circuit Breaker	Fail fast on repeated failures	Resilience4j
Service Discovery	Dynamic registration and discovery	Eureka, Consul
Configuration Server	Central config management	Spring Cloud Config
Saga Pattern	Distributed transaction management	Kafka-based Orchestration

5. What Are the Different Ways to Handle Fault Tolerance?

Strategy	Description	Tools
Retry	Re-attempt failed calls	Spring Retry
Circuit Breaker	Prevent repeated failures	Resilience4j
Bulkhead	Isolate service failures	Resilience4j
Fallback	Provide default response	Resilience4j, Hystrix

Circuit Breaker with Fallback Example:

@CircuitBreaker(name = "productService", fallbackMethod = "fallback")
public String callProductService() {
    return restTemplate.getForObject("http://localhost:8081/products", String.class);
}

public String fallback(Throwable t) {
    return "Default product response";
}

Thanks for Reading.