Spring Boot + Resilience4j is a popular combo for building fault-tolerant, resilient microservices.
Resilience4j provides resilience patterns like:
- CircuitBreaker – prevents cascading failures by stopping calls when downstream is unhealthy.
- Retry – automatically retries failed calls.
- RateLimiter – limits number of requests.
- Bulkhead – limits concurrent calls.
- TimeLimiter – sets timeouts for calls.
✅ Step 1: Add Dependencies
In your pom.xml (Maven):
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<!-- Resilience4j -->
<dependency>
<groupId>io.github.resilience4j</groupId>
<artifactId>resilience4j-spring-boot2</artifactId>
<version>2.2.0</version>
</dependency>
<!-- For circuit breaker metrics (optional with Actuator) -->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
</dependencies>
✅ Step 2: Configure Resilience4j in application.yml
resilience4j:
circuitbreaker:
instances:
myServiceCB:
registerHealthIndicator: true
slidingWindowSize: 5
failureRateThreshold: 50
waitDurationInOpenState: 10s
permittedNumberOfCallsInHalfOpenState: 3
retry:
instances:
myServiceRetry:
maxAttempts: 3
waitDuration: 2s
✅ Step 3: Create a Service with CircuitBreaker + Retry
import io.github.resilience4j.circuitbreaker.annotation.CircuitBreaker;
import io.github.resilience4j.retry.annotation.Retry;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;
@Service
public class MyService {
private final RestTemplate restTemplate = new RestTemplate();
private static final String SERVICE_NAME = "myServiceCB";
@CircuitBreaker(name = SERVICE_NAME, fallbackMethod = "fallbackResponse")
@Retry(name = "myServiceRetry")
public String callExternalService() {
String url = "http://localhost:8081/external/api";
return restTemplate.getForObject(url, String.class);
}
// Fallback method
public String fallbackResponse(Throwable t) {
return "External service unavailable. Please try later.";
}
}
✅ Step 4: Expose an API Endpoint
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class MyController {
private final MyService myService;
public MyController(MyService myService) {
this.myService = myService;
}
@GetMapping("/test")
public String test() {
return myService.callExternalService();
}
}
✅ Step 5: Run and Test
- Start your Spring Boot app.
- Call
/test. - If the external service is up → returns response.
- If down → it will retry 3 times, then trigger the fallback.