5. GatewayFilter Factories

The AddRequestHeader GatewayFilter Factory takes a name and value parameter.

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: add_request_header_route
        uri: https://example.org
        filters:
        - AddRequestHeader=X-Request-Foo, Bar

This will add X-Request-Foo:Bar header to the downstream request’s headers for all matching requests.

The AddRequestParameter GatewayFilter Factory takes a name and value parameter.

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: add_request_parameter_route
        uri: https://example.org
        filters:
        - AddRequestParameter=foo, bar

This will add foo=bar to the downstream request’s query string for all matching requests.

The AddResponseHeader GatewayFilter Factory takes a name and value parameter.

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: add_request_header_route
        uri: https://example.org
        filters:
        - AddResponseHeader=X-Response-Foo, Bar

This will add X-Response-Foo:Bar header to the downstream response’s headers for all matching requests.

Hystrix is a library from Netflix that implements the circuit breaker pattern. The Hystrix GatewayFilter allows you to introduce circuit breakers to your gateway routes, protecting your services from cascading failures and allowing you to provide fallback responses in the event of downstream failures.

To enable Hystrix GatewayFilters in your project, add a dependency on spring-cloud-starter-netflix-hystrix from Spring Cloud Netflix.

The Hystrix GatewayFilter Factory requires a single name parameter, which is the name of the HystrixCommand.

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: hystrix_route
        uri: https://example.org
        filters:
        - Hystrix=myCommandName

This wraps the remaining filters in a HystrixCommand with command name myCommandName.

The Hystrix filter can also accept an optional fallbackUri parameter. Currently, only forward: schemed URIs are supported. If the fallback is called, the request will be forwarded to the controller matched by the URI.

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: hystrix_route
        uri: lb://backing-service:8088
        predicates:
        - Path=/consumingserviceendpoint
        filters:
        - name: Hystrix
          args:
            name: fallbackcmd
            fallbackUri: forward:/incaseoffailureusethis
        - RewritePath=/consumingserviceendpoint, /backingserviceendpoint

This will forward to the /incaseoffailureusethis URI when the Hystrix fallback is called. Note that this example also demonstrates (optional) Spring Cloud Netflix Ribbon load-balancing via the lb prefix on the destination URI.

The primary scenario is to use the fallbackUri to an internal controller or handler within the gateway app. However, it is also possible to reroute the request to a controller or handler in an external application, like so:

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: ingredients
        uri: lb://ingredients
        predicates:
        - Path=//ingredients/**
        filters:
        - name: Hystrix
          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 app, registered under http://localhost:9994.

In case of the request being forwarded to fallback, the Hystrix Gateway filter also provides the Throwable that has caused it. It’s added to the ServerWebExchange as the ServerWebExchangeUtils.HYSTRIX_EXECUTION_EXCEPTION_ATTR attribute that can be used when handling the fallback within the gateway app.

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

Hystrix settings (such as timeouts) can be configured with global defaults or on a route by route basis using application properties as explained on the Hystrix wiki.

To set a 5 second timeout for the example route above, the following configuration would be used:

application.yml. 

hystrix.command.fallbackcmd.execution.isolation.thread.timeoutInMilliseconds: 5000

The FallbackHeaders factory allows you to add Hystrix execution exception details in headers of a request forwarded to a fallbackUri in an external application, like in the following scenario:

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: ingredients
        uri: lb://ingredients
        predicates:
        - Path=//ingredients/**
        filters:
        - name: Hystrix
          args:
            name: fetchIngredients
            fallbackUri: forward:/fallback
      - id: ingredients-fallback
        uri: http://localhost:9994
        predicates:
        - Path=/fallback
        filters:
        - name: FallbackHeaders
          args:
            executionExceptionTypeHeaderName: Test-Header

In this example, after an execution exception occurs while running the HystrixCommand, the request will be forwarde to the fallback endpoint or handler in an app running on localhost:9994. The headers with the exception type, message and -if available- root cause exception type and message will be added to that request by the FallbackHeaders filter.

The names of the headers can be overwritten in the config by setting the values of the arguments listed below, along with their default values:

You can find more information on how Hystrix works with Gateway in the Hystrix GatewayFilter Factory section.

The PrefixPath GatewayFilter Factory takes a single prefix parameter.

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: prefixpath_route
        uri: https://example.org
        filters:
        - PrefixPath=/mypath

This will prefix /mypath to the path of all matching requests. So a request to /hello, would be sent to /mypath/hello.

The PreserveHostHeader GatewayFilter Factory has not parameters. This filter, sets a request attribute that the routing filter will inspect to determine if the original host header should be sent, rather than the host header determined by the http client.

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: preserve_host_route
        uri: https://example.org
        filters:
        - PreserveHostHeader

The RequestRateLimiter GatewayFilter Factory is uses a RateLimiter implementation to determine if the current request is allowed to proceed. If it is not, a status of HTTP 429 - Too Many Requests (by default) is returned.

This filter takes an optional keyResolver parameter and parameters specific to the rate limiter (see below).

keyResolver is a bean that implements the KeyResolver interface. In configuration, reference the bean by name using SpEL. #{@myKeyResolver} is a SpEL expression referencing a bean with the name myKeyResolver.

KeyResolver.java. 

public interface KeyResolver {
	Mono<String> resolve(ServerWebExchange exchange);
}

The KeyResolver interface allows pluggable strategies to derive the key for limiting requests. In future milestones, there will be some KeyResolver implementations.

The default implementation of KeyResolver is the PrincipalNameKeyResolver which retrieves the Principal from the ServerWebExchange and calls Principal.getName().

By default, if the KeyResolver does not find a key, requests will be denied. This behavior can be adjust with the spring.cloud.gateway.filter.request-rate-limiter.deny-empty-key (true or false) and spring.cloud.gateway.filter.request-rate-limiter.empty-key-status-code properties.

	Note
	The RequestRateLimiter is not configurable via the "shortcut" notation. The example below is invalid

application.properties. 

# INVALID SHORTCUT CONFIGURATION
spring.cloud.gateway.routes[0].filters[0]=RequestRateLimiter=2, 2, #{@userkeyresolver}

spring:
  cloud:
    gateway:
      routes:
      - id: requestratelimiter_route
        uri: https://example.org
        filters:
        - name: RequestRateLimiter
          args:
            redis-rate-limiter.replenishRate: 10
            redis-rate-limiter.burstCapacity: 20

@Bean
KeyResolver userKeyResolver() {
    return exchange -> Mono.just(exchange.getRequest().getQueryParams().getFirst("user"));
}

spring:
  cloud:
    gateway:
      routes:
      - id: requestratelimiter_route
        uri: https://example.org
        filters:
        - name: RequestRateLimiter
          args:
            rate-limiter: "#{@myRateLimiter}"
            key-resolver: "#{@userKeyResolver}"

The RedirectTo GatewayFilter Factory takes a status and a url parameter. The status should be a 300 series redirect http code, such as 301. The url should be a valid url. This will be the value of the Location header.

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: prefixpath_route
        uri: https://example.org
        filters:
        - RedirectTo=302, https://acme.org

This will send a status 302 with a Location:https://acme.org header to perform a redirect.

The RemoveHopByHopHeadersFilter GatewayFilter Factory removes headers from forwarded requests. The default list of headers that is removed comes from the IETF.

To change this, set the spring.cloud.gateway.filter.remove-non-proxy-headers.headers property to the list of header names to remove.

The RemoveRequestHeader GatewayFilter Factory takes a name parameter. It is the name of the header to be removed.

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: removerequestheader_route
        uri: https://example.org
        filters:
        - RemoveRequestHeader=X-Request-Foo

This will remove the X-Request-Foo header before it is sent downstream.

The RemoveResponseHeader GatewayFilter Factory takes a name parameter. It is the name of the header to be removed.

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: removeresponseheader_route
        uri: https://example.org
        filters:
        - RemoveResponseHeader=X-Response-Foo

This will remove the X-Response-Foo header from the response before it is returned to the gateway client.

To remove any kind of sensitive header you should configure this filter for any routes that you may want to do so. In addition you can configure this filter once using spring.cloud.gateway.default-filters and have it applied to all routes.

The RewritePath GatewayFilter Factory takes a path regexp parameter and a replacement parameter. This uses Java regular expressions for a flexible way to rewrite the request path.

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: rewritepath_route
        uri: https://example.org
        predicates:
        - Path=/foo/**
        filters:
        - RewritePath=/foo/(?<segment>.*), /$\{segment}

For a request path of /foo/bar, this will set the path to /bar before making the downstream request. Notice the $\ which is replaced with $ because of the YAML spec.

The RewriteResponseHeader GatewayFilter Factory takes name, regexp, and replacement parameters. It uses Java regular expressions for a flexible way to rewrite the response header value.

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: rewriteresponseheader_route
        uri: https://example.org
        filters:
        - RewriteResponseHeader=X-Response-Foo, , password=[^&]+, password=***

For a header value of /42?user=ford&password=omg!what&flag=true, it will be set to /42?user=ford&password=***&flag=true after making the downstream request. Please use $\ to mean $ because of the YAML spec.

The SaveSession GatewayFilter Factory forces a WebSession::save operation before forwarding the call downstream. This is of particular use when using something like Spring Session with a lazy data store and need to ensure the session state has been saved before making the forwarded call.

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: save_session
        uri: https://example.org
        predicates:
        - Path=/foo/**
        filters:
        - SaveSession

If you are integrating Spring Security with Spring Session, and want to ensure security details have been forwarded to the remote process, this is critical.

The SecureHeaders GatewayFilter Factory adds a number of headers to the response at the reccomendation from this blog post.

To change the default values set the appropriate property in the spring.cloud.gateway.filter.secure-headers namespace:

The SetPath GatewayFilter Factory takes a path template parameter. It offers a simple way to manipulate the request path by allowing templated segments of the path. This uses the uri templates from Spring Framework. Multiple matching segments are allowed.

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: setpath_route
        uri: https://example.org
        predicates:
        - Path=/foo/{segment}
        filters:
        - SetPath=/{segment}

For a request path of /foo/bar, this will set the path to /bar before making the downstream request.

The SetResponseHeader GatewayFilter Factory takes name and value parameters.

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: setresponseheader_route
        uri: https://example.org
        filters:
        - SetResponseHeader=X-Response-Foo, Bar

This GatewayFilter replaces all headers with the given name, rather than adding. So if the downstream server responded with a X-Response-Foo:1234, this would be replaced with X-Response-Foo:Bar, which is what the gateway client would receive.

The SetStatus GatewayFilter Factory takes a single status parameter. It must be a valid Spring HttpStatus. It may be the integer value 404 or the string representation of the enumeration NOT_FOUND.

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: setstatusstring_route
        uri: https://example.org
        filters:
        - SetStatus=BAD_REQUEST
      - id: setstatusint_route
        uri: https://example.org
        filters:
        - SetStatus=401

In either case, the HTTP status of the response will be set to 401.

The StripPrefix GatewayFilter Factory takes one paramter, parts. The parts parameter indicated the number of parts in the path to strip from the request before sending it downstream.

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: nameRoot
        uri: http://nameservice
        predicates:
        - Path=/name/**
        filters:
        - StripPrefix=2

When a request is made through the gateway to /name/bar/foo the request made to nameservice will look like http://nameservice/foo.

The Retry GatewayFilter Factory takes retries, statuses, methods, and series as parameters.

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: retry_test
        uri: http://localhost:8080/flakey
        predicates:
        - Host=*.retry.com
        filters:
        - name: Retry
          args:
            retries: 3
            statuses: BAD_GATEWAY

	Note
	The retry filter does not currently support retrying with a body (e.g. for POST or PUT requests with a body).

Note

When using the retry filter with a forward: prefixed URL, the target endpoint should be written carefully so that in case of an error it does not do anything that could result in a response being sent to the client and committed. For example, if the target endpoint is an annotated controller, the target controller method should not return ResponseEntity with an error status code. Instead it should throw an Exception, or signal an error, e.g. via a Mono.error(ex) return value, which the retry filter can be configured to handle by retrying.

The RequestSize GatewayFilter Factory can restrict a request from reaching the downstream service , when the request size is greater than the permissible limit. The filter takes RequestSize as parameter which is the permissible size limit of the request defined in bytes.

application.yml. 

spring:
  cloud:
    gateway:
      routes:
      - id: request_size_route
      uri: http://localhost:8080/upload
      predicates:
      - Path=/upload
      filters:
      - name: RequestSize
        args:
          maxSize: 5000000

The RequestSize GatewayFilter Factory set the response status as 413 Payload Too Large with a additional header errorMessage when the Request is rejected due to size. Following is an example of such an errorMessage .

errorMessage : Request size is larger than permissible limit. Request size is 6.0 MB where permissible limit is 5.0 MB

	Note
	The default Request size will be set to 5 MB if not provided as filter argument in route definition.

This filter is considered BETA and the API may change in the future

This filter can be used to modify the request body before it is sent downstream by the Gateway.

	Note
	This filter can only be configured using the Java DSL

@Bean
public RouteLocator routes(RouteLocatorBuilder builder) {
    return builder.routes()
        .route("rewrite_request_obj", r -> r.host("*.rewriterequestobj.org")
            .filters(f -> f.prefixPath("/httpbin")
                .modifyRequestBody(String.class, Hello.class, MediaType.APPLICATION_JSON_VALUE,
                    (exchange, s) -> return Mono.just(new Hello(s.toUpperCase())))).uri(uri))
        .build();
}

static class Hello {
    String message;

    public Hello() { }

    public Hello(String message) {
        this.message = message;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }
}

This filter is considered BETA and the API may change in the future

This filter can be used to modify the response body before it is sent back to the Client.

	Note
	This filter can only be configured using the Java DSL

@Bean
public RouteLocator routes(RouteLocatorBuilder builder) {
    return builder.routes()
        .route("rewrite_response_upper", r -> r.host("*.rewriteresponseupper.org")
            .filters(f -> f.prefixPath("/httpbin")
        		.modifyResponseBody(String.class, String.class,
        		    (exchange, s) -> Mono.just(s.toUpperCase()))).uri(uri)
        .build();
}

If you would like to add a filter and apply it to all routes you can use spring.cloud.gateway.default-filters. This property takes a list of filters

application.yml. 

spring:
  cloud:
    gateway:
      default-filters:
      - AddResponseHeader=X-Response-Default-Foo, Default-Bar
      - PrefixPath=/httpbin