Circuit Breaker with Resilience4j

1. pom.xml

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-circuitbreaker-resilience4j</artifactId>
</dependency>

2. application.yml (Resilience4j Config)

resilience4j:
  circuitbreaker:
    instances:
      paymentServiceCB:
        failure-rate-threshold: 50 # Open circuit if 50% of calls fail
        wait-duration-in-open-state: 10s # Stay open for 10 seconds
        sliding-window-size: 4 # Look at last 4 calls

3. The Service Code with Fallback (PaymentService.java)

package com.devinhyderabad;

import io.github.resilience4j.circuitbreaker.annotation.CircuitBreaker;
import org.springframework.stereotype.Service;

@Service
public class PaymentService {

    private final PaymentClient paymentClient;

    public PaymentService(PaymentClient paymentClient) {
        this.paymentClient = paymentClient;
    }

    // 1. If this method fails, route to fallbackPayment
    @CircuitBreaker(name = "paymentServiceCB", fallbackMethod = "fallbackPayment")
    public String processPayment(Long userId) {
        return paymentClient.getPaymentStatus(userId); // Might fail
    }

    // 2. Fallback method (Must have same signature + Exception param)
    public String fallbackPayment(Long userId, Exception e) {
        return "Payment service is currently down. Please try again later. (Fallback)";
    }
}