Minimal Guide to Resilience4j and Circuit Breaker in Spring Boot

What is a Circuit Breaker? ## 1. Resilience4j Configuration ## 2. Implementation with Annotations ## 2. Implementation with Annotations ## 3. Other Resilience4j Modules ## Conclusions ## Related Links Resilience4j is a library designed to guarantee application availability, mainly in high-load environments. With the rise of Microservices, it has become essential to control what happens when one of our services fails or is slow to respond, preventing a "cascading failure." The Circuit Breaker pattern works similarly to electrical breakers in a house. If it detects a failure, it "opens" the circuit to prevent further damage and "closes" it once the problem is resolved. A Circuit Breaker has three main states: To start, we create a Spring Boot project and add the following dependency: In our application.yml, we define the parameters that will govern the behavior of our Circuit Breaker: The easiest way to use it is by using the @CircuitBreaker annotation. We must specify the name of the instance we configured in the YAML and a fallback method. Note: The fallback method must have the same signature as the original method, but it must also receive a Throwable or Exception as an argument. The easiest way to use it is by using the @CircuitBreaker annotation. We must specify the name of the instance we configured in the YAML and a fallback method. Note: The fallback method must have the same signature as the original method, but it must also receive a Throwable or Exception as an argument. While the Circuit Breaker is the most famous, Resilience4j offers other tools to improve stability: TimeLimiter Used to set a maximum execution time for a request. If the service doesn't respond within the timeframe, it triggers a failure. Retry Allows us to automatically retry a failed operation a specific number of times before giving up. Bulkhead Limits the number of concurrent calls to a service to avoid saturating resources (like thread pools). Resilience4j is a powerful tool for building robust Microservices. By implementing the Circuit Breaker pattern, we ensure that our application can fail gracefully instead of crashing completely under pressure. Templates let you quickly answer FAQs or store snippets for re-use. Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink. Hide child comments as well For further actions, you may consider blocking this person and/or reporting abuse CODE_BLOCK: <dependency> <groupId>io.github.resilience4j</groupId> <artifactId>resilience4j-spring-boot2</artifactId> </dependency> Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: <dependency> <groupId>io.github.resilience4j</groupId> <artifactId>resilience4j-spring-boot2</artifactId> </dependency> CODE_BLOCK: <dependency> <groupId>io.github.resilience4j</groupId> <artifactId>resilience4j-spring-boot2</artifactId> </dependency> CODE_BLOCK: resilience4j: circuitbreaker: instances: mainService: registerHealthIndicator: true slidingWindowSize: 10 permittedNumberOfCallsInHalfOpenState: 3 slidingWindowType: COUNT_BASED minimumNumberOfCalls: 5 waitDurationInOpenState: 10s failureRateThreshold: 50 eventConsumerBufferSize: 10 Enter fullscreen mode Exit fullscreen mode CODE_BLOCK: resilience4j: circuitbreaker: instances: mainService: registerHealthIndicator: true slidingWindowSize: 10 permittedNumberOfCallsInHalfOpenState: 3 slidingWindowType: COUNT_BASED minimumNumberOfCalls: 5 waitDurationInOpenState: 10s failureRateThreshold: 50 eventConsumerBufferSize: 10 CODE_BLOCK: resilience4j: circuitbreaker: instances: mainService: registerHealthIndicator: true slidingWindowSize: 10 permittedNumberOfCallsInHalfOpenState: 3 slidingWindowType: COUNT_BASED minimumNumberOfCalls: 5 waitDurationInOpenState: 10s failureRateThreshold: 50 eventConsumerBufferSize: 10 COMMAND_BLOCK: @Service public class ProductService { @CircuitBreaker(name = "mainService", fallbackMethod = "fallbackGetProducts") public List<Product> getProducts() { // Logic that might fail (e.g., calling an external API) return externalApi.fetchProducts(); } // Fallback Method public List<Product> fallbackGetProducts(Throwable e) { return List.of(new Product("Default Product", 0.0)); } } Enter fullscreen mode Exit fullscreen mode COMMAND_BLOCK: @Service public class ProductService { @CircuitBreaker(name = "mainService", fallbackMethod = "fallbackGetProducts") public List<Product> getProducts() { // Logic that might fail (e.g., calling an external API) return externalApi.fetchProducts(); } // Fallback Method public List<Product> fallbackGetProducts(Throwable e) { return List.of(new Product("Default Product", 0.0)); } } COMMAND_BLOCK: @Service public class ProductService { @CircuitBreaker(name = "mainService", fallbackMethod = "fallbackGetProducts") public List<Product> getProducts() { // Logic that might fail (e.g., calling an external API) return externalApi.fetchProducts(); } // Fallback Method public List<Product> fallbackGetProducts(Throwable e) { return List.of(new Product("Default Product", 0.0)); } } - Closed: Everything is working correctly. Requests flow normally. - Open: Failures have exceeded the allowed threshold. Requests are blocked and a fallback is executed. - Half-Open: A trial period where a limited number of requests are allowed to check if the service has recovered. - slidingWindowSize: The number of calls to record when the circuit is closed. - failureRateThreshold: The percentage of failures (e.g., 50%) at which the circuit should open. - waitDurationInOpenState: How long the circuit stays "Open" before trying to recover. - permittedNumberOfCallsInHalfOpenState: Number of successful calls needed in "Half-Open" to close the circuit again . - Post in spanish