Spring Cloud CircuitBreaker GatewayFilter Factory

The Spring Cloud CircuitBreaker GatewayFilter factory uses the Spring Cloud CircuitBreaker APIs to wrap Gateway routes in a circuit breaker. Spring Cloud CircuitBreaker supports two libraries that can be used with Spring Cloud Gateway, Hystrix and Resilience4J. Since Netflix has placed Hystrix in maintenance-only mode, we suggest that you use Resilience4J.

To enable the Spring Cloud CircuitBreaker filter, you need to place either spring-cloud-starter-circuitbreaker-reactor-resilience4j or spring-cloud-starter-netflix-hystrix on the classpath. The following example configures a Spring Cloud CircuitBreaker GatewayFilter:

Example 1. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: circuitbreaker_route
        uri: https://example.org
        filters:
        - CircuitBreaker=myCircuitBreaker

To configure the circuit breaker, see the configuration for the underlying circuit breaker implementation you are using.

The Spring Cloud CircuitBreaker filter can also accept an optional fallbackUri parameter. Currently, only forward: schemed URIs are supported. If the fallback is called, the request is forwarded to the controller matched by the URI. The following example configures such a fallback:

Example 2. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: circuitbreaker_route
        uri: lb://backing-service:8088
        predicates:
        - Path=/consumingServiceEndpoint
        filters:
        - name: CircuitBreaker
          args:
            name: myCircuitBreaker
            fallbackUri: forward:/inCaseOfFailureUseThis
        - RewritePath=/consumingServiceEndpoint, /backingServiceEndpoint

The following listing does the same thing in Java:

Example 3. Application.java
@Bean
public RouteLocator routes(RouteLocatorBuilder builder) {
    return builder.routes()
        .route("circuitbreaker_route", r -> r.path("/consumingServiceEndpoint")
            .filters(f -> f.circuitBreaker(c -> c.name("myCircuitBreaker").fallbackUri("forward:/inCaseOfFailureUseThis"))
                .rewritePath("/consumingServiceEndpoint", "/backingServiceEndpoint")).uri("lb://backing-service:8088")
        .build();
}

This example forwards to the /inCaseofFailureUseThis URI when the circuit breaker fallback is called. Note that this example also demonstrates the (optional) Spring Cloud Netflix Ribbon load-balancing (defined by the lb prefix on the destination URI).

The primary scenario is to use the fallbackUri to define an internal controller or handler within the gateway application. However, you can also reroute the request to a controller or handler in an external application, as follows:

Example 4. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: ingredients
        uri: lb://ingredients
        predicates:
        - Path=//ingredients/**
        filters:
        - name: CircuitBreaker
          args:
            name: fetchIngredients
            fallbackUri: forward:/fallback
      - id: ingredients-fallback
        uri: http://localhost:9994
        predicates:
        - Path=/fallback

In this example, there is no fallback endpoint or handler in the gateway application. However, there is one in another application, registered under http://localhost:9994.

In case of the request being forwarded to fallback, the Spring Cloud CircuitBreaker Gateway filter also provides the Throwable that has caused it. It is added to the ServerWebExchange as the ServerWebExchangeUtils.CIRCUITBREAKER_EXECUTION_EXCEPTION_ATTR attribute that can be used when handling the fallback within the gateway application.

For the external controller/handler scenario, headers can be added with exception details. You can find more information on doing so in the FallbackHeaders GatewayFilter Factory section.