`FallbackHeaders` Filter

The FallbackHeaders factory lets you add Spring Cloud CircuitBreaker execution exception details in the headers of a request forwarded to a fallbackUri in an external application, as in the following scenario:

application.yml

spring:
  cloud:
    gateway:
      mvc:
        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
          filters:
          - name: FallbackHeaders
            args:
              executionExceptionTypeHeaderName: Test-Header

GatewaySampleApplication.java

import static org.springframework.cloud.gateway.server.mvc.filter.CircuitBreakerFilterFunctions.circuitBreaker;
import static org.springframework.cloud.gateway.server.mvc.filter.BeforeFilterFunctions.fallbackHeaders;
import static org.springframework.cloud.gateway.server.mvc.filter.LoadBalancerFilterFunctions.lb;
import static org.springframework.cloud.gateway.server.mvc.handler.GatewayRouterFunctions.route;
import static org.springframework.cloud.gateway.server.mvc.handler.HandlerFunctions.http;

@Configuration
class RouteConfiguration {

    @Bean
    public RouterFunction<ServerResponse> gatewayRouterFunctionsCircuitBreakerFallbackToGatewayRoute() {
        return route("ingredients")
                .route(path("/ingredients/**"), http())
                .filter(lb("ingredients"))
                .filter(circuitBreaker("fetchIngredients", URI.create("forward:/fallback")))
                .build()
            .and(route("ingredients-fallback")
                .route(path("/fallback"), http("http://localhost:9994"))
                .before(fallbackHeaders())
                .build());
    }
}

In this example, after an execution exception occurs while running the circuit breaker, the request is forwarded to the fallback endpoint or handler in an application running on localhost:9994. The headers with the exception type, message and (if available) root cause exception type and message are added to that request by the FallbackHeaders filter.

You can overwrite the names of the headers in the configuration by setting the values of the following arguments (shown with their default values):

executionExceptionTypeHeaderName ("Execution-Exception-Type")
executionExceptionMessageHeaderName ("Execution-Exception-Message")
rootCauseExceptionTypeHeaderName ("Root-Cause-Exception-Type")
rootCauseExceptionMessageHeaderName ("Root-Cause-Exception-Message")

For more information on circuit breakers and the gateway see the Spring Cloud CircuitBreaker Filter section.

FallbackHeaders Filter

`FallbackHeaders` Filter