Spring Boot Circuit Breaker is a fault-tolerance mechanism used to prevent cascading failures in a microservices architecture. It helps applications handle failures gracefully by detecting failures and stopping excessive requests to unhealthy services. This guide will walk you through implementing Circuit Breaker using Resilience4j in Spring Boot.
In this section, we clarify Why Use Circuit Breaker? and summarize the key points you will apply in implementation.
Ensure you have the following:
In this section, we clarify Step 1: Add Dependencies and summarize the key points you will apply in implementation.
Maven:
<dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-circuitbreaker-resilience4j</artifactId> </dependency>
Gradle:
implementation 'org.springframework.cloud:spring-cloud-starter-circuitbreaker-resilience4j'
Define Circuit Breaker settings in application.yml.
resilience4j: circuitbreaker: instances: externalService: failure-rate-threshold: 50 slow-call-rate-threshold: 50 slow-call-duration-threshold: 2000ms permitted-number-of-calls-in-half-open-state: 3 sliding-window-size: 10 minimum-number-of-calls: 5 wait-duration-in-open-state: 5s
In this section, we clarify Step 3: Implement Circuit Breaker in a REST Service and summarize the key points you will apply in implementation.
The following example gives practical context for Create a Service to Call an External API and can be applied directly.
Start the application:
./mvnw spring-boot:run
or using Gradle:
gradle bootRun
Test the Circuit Breaker:
curl -X GET http://localhost:8080/api/data
You now have a practical Spring Boot Circuit Breaker implementation with a clear, production-friendly Spring Boot structure. As a next step, adapt configuration and tests to your own domain, then validate behavior under realistic traffic and failure scenarios.
package com.example.circuitbreaker.service; import io.github.resilience4j.circuitbreaker.annotation.CircuitBreaker; import org.springframework.stereotype.Service; import org.springframework.web.client.RestTemplate; @Service public class ExternalService { private final RestTemplate restTemplate = new RestTemplate(); @CircuitBreaker(name = "externalService", fallbackMethod = "fallbackResponse") public String callExternalAPI() { return restTemplate.getForObject("http://unreliable-service/api/data", String.class); } public String fallbackResponse(Exception e) { return "Fallback response: Service is unavailable!"; } }
package com.example.circuitbreaker.service import io.github.resilience4j.circuitbreaker.annotation.CircuitBreaker import org.springframework.stereotype.Service import org.springframework.web.client.RestTemplate @Service class ExternalService { private val restTemplate = RestTemplate() @CircuitBreaker(name = "externalService", fallbackMethod = "fallbackResponse") fun callExternalAPI(): String { return restTemplate.getForObject("http://unreliable-service/api/data", String::class.java) ?: "" } fun fallbackResponse(e: Exception): String { return "Fallback response: Service is unavailable!" } }
package com.example.circuitbreaker.controller; import com.example.circuitbreaker.service.ExternalService; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RestController; @RestController @RequestMapping("/api") public class CircuitBreakerController { private final ExternalService externalService; public CircuitBreakerController(ExternalService externalService) { this.externalService = externalService; } @GetMapping("/data") public String fetchData() { return externalService.callExternalAPI(); } }
package com.example.circuitbreaker.controller import com.example.circuitbreaker.service.ExternalService import org.springframework.web.bind.annotation.GetMapping import org.springframework.web.bind.annotation.RequestMapping import org.springframework.web.bind.annotation.RestController @RestController @RequestMapping("/api") class CircuitBreakerController(private val externalService: ExternalService) { @GetMapping("/data") fun fetchData(): String { return externalService.callExternalAPI() } }
