Service Resilience using Resilience4j Circuit Breaker – Microservices Essentials

In a microservices environment, a single failing service can cascade and cause other services to fail. To prevent this, we use Resilience4j to implement Circuit Breaker patterns that provide graceful degradation and stability. Service Resilience — ensuring that your system remains responsive and fault-tolerant under failure conditions

In this tutorial,

🛠️ Step 1: Setup Prerequisites

✅ Prerequisites:

• Java 17 installed
• Maven installed
• IDE (IntelliJ / VS Code / Eclipse)
• Postman or browser to test API

📁 Step 2: Create product-service Microservice

2.1 Create Spring Boot Project

Use Spring Initializr:

• Project: Maven
• Language: Java
• Spring Boot: 3.1.8
• Group: com.example
• Artifact: product-service
• Dependencies:
  • Spring Web
  • Spring Boot Actuator

Click Generate, extract ZIP, and open in IDE.

2.3 ProductController.java

package com.example.productservice.controller;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class ProductController {
    @GetMapping("/products")
    public String getProducts() {
        return "List of products from PRODUCT-SERVICE";
    }
}

2.4 application.properties

server.port=8082
spring.application.name=product-service

📁 Step 3: Create user-service Microservice

3.1 Create Another Spring Boot Project

Use Spring Initializr:

• Artifact: user-service
• Dependencies:
  • Spring Web
  • Spring Boot Actuator
  • Resilience4j
  • Spring Boot Starter AOP (required by Resilience4j)

3.2 pom.xml for user-service

<dependencies>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-web</artifactId>
	</dependency>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-actuator</artifactId>
	</dependency>
	<dependency>
		<groupId>io.github.resilience4j</groupId>
		<artifactId>resilience4j-spring-boot3</artifactId>
	</dependency>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-aop</artifactId>
	</dependency>
</dependencies>

3.3 UserController.java

package com.example.userservice.controller;

import io.github.resilience4j.circuitbreaker.annotation.CircuitBreaker;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

@RestController
public class UserController {

    private final RestTemplate restTemplate;

    @Value("${product.service.url}")
    private String productServiceUrl;

    public UserController() {
        this.restTemplate = new RestTemplate();
    }

    @GetMapping("/users")
    @CircuitBreaker(name = "productServiceBreaker", fallbackMethod = "productFallback")
    public String getUsers() {
        String productResponse = restTemplate.getForObject(productServiceUrl + "/products", String.class);
        return "User Data + " + productResponse;
    }

    public String productFallback(Throwable t) {
        return "Product Service is down. Please try again later.";
    }
}

3.4 application.properties

server.port=8081
spring.application.name=user-service
product.service.url=http://localhost:8082

Step 4: Test Without Circuit Breaker

1. Start product-service (port 8082)
2. Start user-service (port 8081)
3. Call: http://localhost:8081/users
   → You should see User Data + List of products from PRODUCT-SERVICE

Step 5: Test Circuit Breaker

1. Stop product-service
2. Call: http://localhost:8081/users
   → You should now see:
   "Product Service is down. Please try again later."

Step 6: Enable Actuator for Circuit Breaker Monitoring (Optional)

Add to application.properties:

management.endpoints.web.exposure.include=*

You can then check:

http://localhost:8081/actuator/circuitbreakers
http://localhost:8081/actuator/health

Github code : https://github.com/infotechseo/resilience4j-circuit-breaker