Resilience with Circuit Breakers and Retry Mechanisms (Resilience4j)[Java Spring Boot Mastery Series – Part 21]

In microservice architecture, failures are inevitable. One failing service should not bring down the entire system. That’s where Resilience4j comes in — a lightweight fault tolerance library for Java.

🧠 Why Resilience?

• Protects your app from cascading failures
• Improves fault tolerance with:
  • Circuit Breaker
  • Retry
  • Rate Limiter
  • Bulkhead
  • Time Limiter
  • Fallbacks

🔧 1. Add Resilience4j Dependencies

👉 pom.xml

<dependency>
  <groupId>io.github.resilience4j</groupId>
  <artifactId>resilience4j-spring-boot3</artifactId>
</dependency>

<dependency>
  <groupId>io.github.resilience4j</groupId>
  <artifactId>resilience4j-micrometer</artifactId>
</dependency>

<dependency>
  <groupId>io.github.resilience4j</groupId>
  <artifactId>resilience4j-all</artifactId>
</dependency>

🔌 2. Enable Resilience4j Circuit Breaker in a REST Client

Sample REST client with fallback

@RestController
@RequestMapping("/api/products")
public class ProductController {

  @Autowired
  private ProductService productService;

  @GetMapping
  @CircuitBreaker(name = "productService", fallbackMethod = "fallbackForGetProducts")
  public ResponseEntity<List<String>> getProducts() {
    return ResponseEntity.ok(productService.fetchProductList());
  }

  public ResponseEntity<List<String>> fallbackForGetProducts(Throwable ex) {
    return ResponseEntity.ok(List.of("DEFAULT_PRODUCT_1", "DEFAULT_PRODUCT_2"));
  }
}

Explanation:

• @CircuitBreaker watches the method.
• If failures exceed the threshold, it opens the circuit.
• Fallback method is triggered when the service is down.

⚙️ 3. Configure Circuit Breaker (application.yml)

resilience4j:
  circuitbreaker:
    instances:
      productService:
        registerHealthIndicator: true
        slidingWindowSize: 5
        minimumNumberOfCalls: 5
        failureRateThreshold: 50
        waitDurationInOpenState: 10s
        permittedNumberOfCallsInHalfOpenState: 2
        automaticTransitionFromOpenToHalfOpenEnabled: true

Description of config:

Property	Meaning
slidingWindowSize	No. of recent calls to consider
failureRateThreshold	% failure to open circuit
waitDurationInOpenState	Wait time before trying again
permittedNumberOfCallsInHalfOpenState	No. of test calls allowed
automaticTransitionFromOpenToHalfOpenEnabled	Auto reattempt after open

🔁 4. Add Retry Mechanism

@GetMapping("/retry")
@Retry(name = "productRetry", fallbackMethod = "retryFallback")
public String retryExample() {
  if (new Random().nextBoolean()) {
    throw new RuntimeException("Simulated failure");
  }
  return "Success after retry";
}

public String retryFallback(Exception ex) {
  return "Fallback after retries";
}

Configuration:

resilience4j:
  retry:
    instances:
      productRetry:
        maxAttempts: 3
        waitDuration: 2s

🧱 5. Rate Limiter

@GetMapping("/limited")
@RateLimiter(name = "productRateLimiter")
public String rateLimiterExample() {
  return "Allowed";
}

Config:

resilience4j:
  ratelimiter:
    instances:
      productRateLimiter:
        limitForPeriod: 5
        limitRefreshPeriod: 1s

This allows 5 calls per second.

🧊 6. Bulkhead (Concurrency Control)

@GetMapping("/bulkhead")
@Bulkhead(name = "productBulkhead", type = Bulkhead.Type.THREADPOOL)
public String bulkheadExample() {
  return "Access granted";
}

Config:

resilience4j:
  bulkhead:
    instances:
      productBulkhead:
        maxConcurrentCalls: 3
        maxWaitDuration: 1s

Restricts the number of concurrent requests.

📊 7. Monitoring with Actuator & Micrometer

Add Actuator and Micrometer

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-actuator</artifactId>
</dependency>

<dependency>
  <groupId>io.micrometer</groupId>
  <artifactId>micrometer-registry-prometheus</artifactId>
</dependency>

application.yml

management:
  endpoints:
    web:
      exposure:
        include: "*"
  endpoint:
    health:
      show-details: always

Metrics available at /actuator/metrics

Prometheus and Grafana can be added for visualization

🔄 8. Summary

Feature	Annotation	Use Case
Circuit Breaker	@CircuitBreaker	Fail fast when service is down
Retry	@Retry	Retry failed calls
Rate Limiter	@RateLimiter	Throttle excessive requests
Bulkhead	@Bulkhead	Limit concurrent executions
Time Limiter	@TimeLimiter	Timeout protection

🛠 Tools It Integrates With

• Spring Boot Actuator
• Micrometer (for monitoring)
• Prometheus & Grafana
• Spring Cloud Gateway (for filtering + retry)
• Spring Retry (alternate retry mechanism)

✅ Next Up: Part 22 – Spring Boot and Kafka Messaging for Event-Driven Architecture