2.2.4.BUILD-SNAPSHOT

This project provides an API Gateway built on top of the Spring Ecosystem, including: Spring 5, Spring Boot 2 and Project Reactor. Spring Cloud Gateway aims to provide a simple, yet effective way to route to APIs and provide cross cutting concerns to them such as: security, monitoring/metrics, and resiliency.

1. How to Include Spring Cloud Gateway

To include Spring Cloud Gateway in your project, use the starter with a group ID of org.springframework.cloud and an artifact ID of spring-cloud-starter-gateway. See the Spring Cloud Project page for details on setting up your build system with the current Spring Cloud Release Train.

If you include the starter, but you do not want the gateway to be enabled, set spring.cloud.gateway.enabled=false.

Spring Cloud Gateway is built on Spring Boot 2.x, Spring WebFlux, and Project Reactor. As a consequence, many of the familiar synchronous libraries (Spring Data and Spring Security, for example) and patterns you know may not apply when you use Spring Cloud Gateway. If you are unfamiliar with these projects, we suggest you begin by reading their documentation to familiarize yourself with some of the new concepts before working with Spring Cloud Gateway.
Spring Cloud Gateway requires the Netty runtime provided by Spring Boot and Spring Webflux. It does not work in a traditional Servlet Container or when built as a WAR.

2. Glossary

  • Route: The basic building block of the gateway. It is defined by an ID, a destination URI, a collection of predicates, and a collection of filters. A route is matched if the aggregate predicate is true.

  • Predicate: This is a Java 8 Function Predicate. The input type is a Spring Framework ServerWebExchange. This lets you match on anything from the HTTP request, such as headers or parameters.

  • Filter: These are instances of Spring Framework GatewayFilter that have been constructed with a specific factory. Here, you can modify requests and responses before or after sending the downstream request.

3. How It Works

The following diagram provides a high-level overview of how Spring Cloud Gateway works:

Spring Cloud Gateway Diagram

Clients make requests to Spring Cloud Gateway. If the Gateway Handler Mapping determines that a request matches a route, it is sent to the Gateway Web Handler. This handler runs the request through a filter chain that is specific to the request. The reason the filters are divided by the dotted line is that filters can run logic both before and after the proxy request is sent. All “pre” filter logic is executed. Then the proxy request is made. After the proxy request is made, the “post” filter logic is run.

URIs defined in routes without a port get default port values of 80 and 443 for the HTTP and HTTPS URIs, respectively.

4. Configuring Route Predicate Factories and Gateway Filter Factories

There are two ways to configure predicates and filters: shortcuts and fully expanded arguments. Most examples below use the shortcut way.

The name and argument names will be listed as code in the first sentance or two of the each section. The arguments are typically listed in the order that would be needed for the shortcut configuration.

4.1. Shortcut Configuration

Shortcut configuration is recognized by the filter name, followed by an equals sign (=), followed by argument values separated by commas (,).

application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: after_route
        uri: https://example.org
        predicates:
        - Cookie=mycookie,mycookievalue

The previous sample defines the Cookie Route Predicate Factory with two arguments, the cookie name, mycookie and the value to match mycookievalue.

4.2. Fully Expanded Arguments

Fully expanded arguments appear more like standard yaml configuration with name/value pairs. Typically, there will be a name key and an args key. The args key is a map of key value pairs to configure the predicate or filter.

application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: after_route
        uri: https://example.org
        predicates:
        - name: Cookie
          args:
            name: mycookie
            regexp: mycookievalue

This is the full configuration of the shortcut configuration of the Cookie predicate shown above.

5. Route Predicate Factories

Spring Cloud Gateway matches routes as part of the Spring WebFlux HandlerMapping infrastructure. Spring Cloud Gateway includes many built-in route predicate factories. All of these predicates match on different attributes of the HTTP request. You can combine multiple route predicate factories with logical and statements.

5.1. The After Route Predicate Factory

The After route predicate factory takes one parameter, a datetime (which is a java ZonedDateTime). This predicate matches requests that happen after the specified datetime. The following example configures an after route predicate:

Example 1. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: after_route
        uri: https://example.org
        predicates:
        - After=2017-01-20T17:42:47.789-07:00[America/Denver]

This route matches any request made after Jan 20, 2017 17:42 Mountain Time (Denver).

5.2. The Before Route Predicate Factory

The Before route predicate factory takes one parameter, a datetime (which is a java ZonedDateTime). This predicate matches requests that happen before the specified datetime. The following example configures a before route predicate:

Example 2. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: before_route
        uri: https://example.org
        predicates:
        - Before=2017-01-20T17:42:47.789-07:00[America/Denver]

This route matches any request made before Jan 20, 2017 17:42 Mountain Time (Denver).

5.3. The Between Route Predicate Factory

The Between route predicate factory takes two parameters, datetime1 and datetime2 which are java ZonedDateTime objects. This predicate matches requests that happen after datetime1 and before datetime2. The datetime2 parameter must be after datetime1. The following example configures a between route predicate:

Example 3. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: between_route
        uri: https://example.org
        predicates:
        - Between=2017-01-20T17:42:47.789-07:00[America/Denver], 2017-01-21T17:42:47.789-07:00[America/Denver]

This route matches any request made after Jan 20, 2017 17:42 Mountain Time (Denver) and before Jan 21, 2017 17:42 Mountain Time (Denver). This could be useful for maintenance windows.

The Cookie route predicate factory takes two parameters, the cookie name and a regexp (which is a Java regular expression). This predicate matches cookies that have the given name and whose values match the regular expression. The following example configures a cookie route predicate factory:

Example 4. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: cookie_route
        uri: https://example.org
        predicates:
        - Cookie=chocolate, ch.p

This route matches requests that have a cookie named chocolate whose value matches the ch.p regular expression.

5.5. The Header Route Predicate Factory

The Header route predicate factory takes two parameters, the header name and a regexp (which is a Java regular expression). This predicate matches with a header that has the given name whose value matches the regular expression. The following example configures a header route predicate:

Example 5. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: header_route
        uri: https://example.org
        predicates:
        - Header=X-Request-Id, \d+

This route matches if the request has a header named X-Request-Id whose value matches the \d+ regular expression (that is, it has a value of one or more digits).

5.6. The Host Route Predicate Factory

The Host route predicate factory takes one parameter: a list of host name patterns. The pattern is an Ant-style pattern with . as the separator. This predicates matches the Host header that matches the pattern. The following example configures a host route predicate:

Example 6. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: host_route
        uri: https://example.org
        predicates:
        - Host=**.somehost.org,**.anotherhost.org

URI template variables (such as {sub}.myhost.org) are supported as well.

This route matches if the request has a Host header with a value of www.somehost.org or beta.somehost.org or www.anotherhost.org.

This predicate extracts the URI template variables (such as sub, defined in the preceding example) as a map of names and values and places it in the ServerWebExchange.getAttributes() with a key defined in ServerWebExchangeUtils.URI_TEMPLATE_VARIABLES_ATTRIBUTE. Those values are then available for use by GatewayFilter factories

5.7. The Method Route Predicate Factory

The Method Route Predicate Factory takes a methods argument which is one or more parameters: the HTTP methods to match. The following example configures a method route predicate:

Example 7. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: method_route
        uri: https://example.org
        predicates:
        - Method=GET,POST

This route matches if the request method was a GET or a POST.

5.8. The Path Route Predicate Factory

The Path Route Predicate Factory takes two parameters: a list of Spring PathMatcher patterns and an optional flag called matchOptionalTrailingSeparator. The following example configures a path route predicate:

Example 8. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: path_route
        uri: https://example.org
        predicates:
        - Path=/red/{segment},/blue/{segment}

This route matches if the request path was, for example: /red/1 or /red/blue or /blue/green.

This predicate extracts the URI template variables (such as segment, defined in the preceding example) as a map of names and values and places it in the ServerWebExchange.getAttributes() with a key defined in ServerWebExchangeUtils.URI_TEMPLATE_VARIABLES_ATTRIBUTE. Those values are then available for use by GatewayFilter factories

A utility method (called get) is available to make access to these variables easier. The following example shows how to use the get method:

Map<String, String> uriVariables = ServerWebExchangeUtils.getPathPredicateVariables(exchange);

String segment = uriVariables.get("segment");

5.9. The Query Route Predicate Factory

The Query route predicate factory takes two parameters: a required param and an optional regexp (which is a Java regular expression). The following example configures a query route predicate:

Example 9. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: query_route
        uri: https://example.org
        predicates:
        - Query=green

The preceding route matches if the request contained a green query parameter.

application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: query_route
        uri: https://example.org
        predicates:
        - Query=red, gree.

The preceding route matches if the request contained a red query parameter whose value matched the gree. regexp, so green and greet would match.

5.10. The RemoteAddr Route Predicate Factory

The RemoteAddr route predicate factory takes a list (min size 1) of sources, which are CIDR-notation (IPv4 or IPv6) strings, such as 192.168.0.1/16 (where 192.168.0.1 is an IP address and 16 is a subnet mask). The following example configures a RemoteAddr route predicate:

Example 10. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: remoteaddr_route
        uri: https://example.org
        predicates:
        - RemoteAddr=192.168.1.1/24

This route matches if the remote address of the request was, for example, 192.168.1.10.

5.11. The Weight Route Predicate Factory

The Weight route predicate factory takes two arguments: group and weight (an int). The weights are calculated per group. The following example configures a weight route predicate:

Example 11. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: weight_high
        uri: https://weighthigh.org
        predicates:
        - Weight=group1, 8
      - id: weight_low
        uri: https://weightlow.org
        predicates:
        - Weight=group1, 2

This route would forward ~80% of traffic to weighthigh.org and ~20% of traffic to weighlow.org

5.11.1. Modifying the Way Remote Addresses Are Resolved

By default, the RemoteAddr route predicate factory uses the remote address from the incoming request. This may not match the actual client IP address if Spring Cloud Gateway sits behind a proxy layer.

You can customize the way that the remote address is resolved by setting a custom RemoteAddressResolver. Spring Cloud Gateway comes with one non-default remote address resolver that is based off of the X-Forwarded-For header, XForwardedRemoteAddressResolver.

XForwardedRemoteAddressResolver has two static constructor methods, which take different approaches to security:

  • XForwardedRemoteAddressResolver::trustAll returns a RemoteAddressResolver that always takes the first IP address found in the X-Forwarded-For header. This approach is vulnerable to spoofing, as a malicious client could set an initial value for the X-Forwarded-For, which would be accepted by the resolver.

  • XForwardedRemoteAddressResolver::maxTrustedIndex takes an index that correlates to the number of trusted infrastructure running in front of Spring Cloud Gateway. If Spring Cloud Gateway is, for example only accessible through HAProxy, then a value of 1 should be used. If two hops of trusted infrastructure are required before Spring Cloud Gateway is accessible, then a value of 2 should be used.

Consider the following header value:

X-Forwarded-For: 0.0.0.1, 0.0.0.2, 0.0.0.3

The following maxTrustedIndex values yield the following remote addresses:

maxTrustedIndex result

[Integer.MIN_VALUE,0]

(invalid, IllegalArgumentException during initialization)

1

0.0.0.3

2

0.0.0.2

3

0.0.0.1

[4, Integer.MAX_VALUE]

0.0.0.1

The following example shows how to achieve the same configuration with Java:

Example 12. GatewayConfig.java
RemoteAddressResolver resolver = XForwardedRemoteAddressResolver
    .maxTrustedIndex(1);

...

.route("direct-route",
    r -> r.remoteAddr("10.1.1.1", "10.10.1.1/24")
        .uri("https://downstream1")
.route("proxied-route",
    r -> r.remoteAddr(resolver, "10.10.1.1", "10.10.1.1/24")
        .uri("https://downstream2")
)

6. GatewayFilter Factories

Route filters allow the modification of the incoming HTTP request or outgoing HTTP response in some manner. Route filters are scoped to a particular route. Spring Cloud Gateway includes many built-in GatewayFilter Factories.

For more detailed examples of how to use any of the following filters, take a look at the unit tests.

6.1. The AddRequestHeader GatewayFilter Factory

The AddRequestHeader GatewayFilter factory takes a name and value parameter. The following example configures an AddRequestHeader GatewayFilter:

Example 13. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: add_request_header_route
        uri: https://example.org
        filters:
        - AddRequestHeader=X-Request-red, blue

This listing adds X-Request-red:blue header to the downstream request’s headers for all matching requests.

AddRequestHeader is aware of the URI variables used to match a path or host. URI variables may be used in the value and are expanded at runtime. The following example configures an AddRequestHeader GatewayFilter that uses a variable:

Example 14. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: add_request_header_route
        uri: https://example.org
        predicates:
        - Path=/red/{segment}
        filters:
        - AddRequestHeader=X-Request-Red, Blue-{segment}

6.2. The AddRequestParameter GatewayFilter Factory

The AddRequestParameter GatewayFilter Factory takes a name and value parameter. The following example configures an AddRequestParameter GatewayFilter:

Example 15. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: add_request_parameter_route
        uri: https://example.org
        filters:
        - AddRequestParameter=red, blue

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

AddRequestParameter is aware of the URI variables used to match a path or host. URI variables may be used in the value and are expanded at runtime. The following example configures an AddRequestParameter GatewayFilter that uses a variable:

Example 16. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: add_request_parameter_route
        uri: https://example.org
        predicates:
        - Host: {segment}.myhost.org
        filters:
        - AddRequestParameter=foo, bar-{segment}

6.3. The AddResponseHeader GatewayFilter Factory

The AddResponseHeader GatewayFilter Factory takes a name and value parameter. The following example configures an AddResponseHeader GatewayFilter:

Example 17. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: add_response_header_route
        uri: https://example.org
        filters:
        - AddResponseHeader=X-Response-Red, Blue

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

AddResponseHeader is aware of URI variables used to match a path or host. URI variables may be used in the value and are expanded at runtime. The following example configures an AddResponseHeader GatewayFilter that uses a variable:

Example 18. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: add_response_header_route
        uri: https://example.org
        predicates:
        - Host: {segment}.myhost.org
        filters:
        - AddResponseHeader=foo, bar-{segment}

6.4. The DedupeResponseHeader GatewayFilter Factory

The DedupeResponseHeader GatewayFilter factory takes a name parameter and an optional strategy parameter. name can contain a space-separated list of header names. The following example configures a DedupeResponseHeader GatewayFilter:

Example 19. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: dedupe_response_header_route
        uri: https://example.org
        filters:
        - DedupeResponseHeader=Access-Control-Allow-Credentials Access-Control-Allow-Origin

This removes duplicate values of Access-Control-Allow-Credentials and Access-Control-Allow-Origin response headers in cases when both the gateway CORS logic and the downstream logic add them.

The DedupeResponseHeader filter also accepts an optional strategy parameter. The accepted values are RETAIN_FIRST (default), RETAIN_LAST, and RETAIN_UNIQUE.

6.5. The Hystrix GatewayFilter Factory

Netflix has put Hystrix in maintenance mode. We suggest you use the Spring Cloud CircuitBreaker Gateway Filter with Resilience4J, as support for Hystrix will be removed in a future release.

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

To enable Hystrix GatewayFilter instances 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. The following example configures a Hystrix GatewayFilter:

Example 20. 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 a command name of 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 is forwarded to the controller matched by the URI. The following example configures such a fallback:

Example 21. 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 (defined 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, you can also reroute the request to a controller or handler in an external application, as follows:

Example 22. 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 application, registered under localhost:9994.

In case of the request being forwarded to the fallback, the Hystrix Gateway filter also provides the Throwable that has caused it. It is added to the ServerWebExchange as the ServerWebExchangeUtils.HYSTRIX_EXECUTION_EXCEPTION_ATTR attribute, which you can use when handling the fallback within the gateway application.

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

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

To set a five-second timeout for the example route shown earlier, you could use the following configuration:

Example 23. application.yml
hystrix.command.fallbackcmd.execution.isolation.thread.timeoutInMilliseconds: 5000

6.6. 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 24. 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 25. 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 26. 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 27. 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 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.

6.7. The FallbackHeaders GatewayFilter Factory

The FallbackHeaders factory lets you add Hystrix or 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:

Example 28. 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
        filters:
        - name: FallbackHeaders
          args:
            executionExceptionTypeHeaderName: Test-Header

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 Hystrix GatewayFilter Factory section or Spring Cloud CircuitBreaker Factory section.

6.8. The MapRequestHeader GatewayFilter Factory

The MapRequestHeader GatewayFilter factory takes fromHeader and toHeader parameters. It creates a new named header (toHeader), and the value is extracted out of an existing named header (fromHeader) from the incoming http request. If the input header does not exist, the filter has no impact. If the new named header already exists, its values are augmented with the new values. The following example configures a MapRequestHeader:

Example 29. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: map_request_header_route
        uri: https://example.org
        filters:
        - MapRequestHeader=Blue, X-Request-Red

This adds X-Request-Red:<values> header to the downstream request with updated values from the incoming HTTP request’s Blue header.

6.9. The PrefixPath GatewayFilter Factory

The PrefixPath GatewayFilter factory takes a single prefix parameter. The following example configures a PrefixPath GatewayFilter:

Example 30. 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.

6.10. The PreserveHostHeader GatewayFilter Factory

The PreserveHostHeader GatewayFilter factory has no parameters. This filter sets a request attribute that the routing filter inspects to determine if the original host header should be sent, rather than the host header determined by the HTTP client. The following example configures a PreserveHostHeader GatewayFilter:

Example 31. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: preserve_host_route
        uri: https://example.org
        filters:
        - PreserveHostHeader

6.11. The RequestRateLimiter GatewayFilter Factory

The RequestRateLimiter GatewayFilter factory 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 (described later in this section).

keyResolver is a bean that implements the KeyResolver interface. In configuration, reference the bean by name using SpEL. #{@myKeyResolver} is a SpEL expression that references a bean named myKeyResolver. The following listing shows the KeyResolver interface:

Example 32. KeyResolver.java
public interface KeyResolver {
    Mono<String> resolve(ServerWebExchange exchange);
}

The KeyResolver interface lets pluggable strategies derive the key for limiting requests. In future milestone releases, 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 are denied. You can adjust this behavior by setting 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.

The RequestRateLimiter is not configurable with the "shortcut" notation. The following example below is invalid:

Example 33. application.properties
# INVALID SHORTCUT CONFIGURATION
spring.cloud.gateway.routes[0].filters[0]=RequestRateLimiter=2, 2, #{@userkeyresolver}

6.11.1. The Redis RateLimiter

The Redis implementation is based off of work done at Stripe. It requires the use of the spring-boot-starter-data-redis-reactive Spring Boot starter.

The algorithm used is the Token Bucket Algorithm.

The redis-rate-limiter.replenishRate property is how many requests per second you want a user to be allowed to do, without any dropped requests. This is the rate at which the token bucket is filled.

The redis-rate-limiter.burstCapacity property is the maximum number of requests a user is allowed to do in a single second. This is the number of tokens the token bucket can hold. Setting this value to zero blocks all requests.

The redis-rate-limiter.requestedTokens property is how many tokens a request costs. This is the number of tokens taken from the bucket for each request and defaults to 1.

A steady rate is accomplished by setting the same value in replenishRate and burstCapacity. Temporary bursts can be allowed by setting burstCapacity higher than replenishRate. In this case, the rate limiter needs to be allowed some time between bursts (according to replenishRate), as two consecutive bursts will result in dropped requests (HTTP 429 - Too Many Requests). The following listing configures a redis-rate-limiter:

Rate limits bellow 1 request/s are accomplished by setting replenishRate to the wanted number of requests, requestedTokens to the timespan in seconds and burstCapacity to the product of replenishRate and requestedTokens, e.g. setting replenishRate=1, requestedTokens=60 and burstCapacity=60 will result in a limit of 1 request/min.

Example 34. application.yml
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
            redis-rate-limiter.requestedTokens: 1

The following example configures a KeyResolver in Java:

Example 35. Config.java
@Bean
KeyResolver userKeyResolver() {
    return exchange -> Mono.just(exchange.getRequest().getQueryParams().getFirst("user"));
}

This defines a request rate limit of 10 per user. A burst of 20 is allowed, but, in the next second, only 10 requests are available. The KeyResolver is a simple one that gets the user request parameter (note that this is not recommended for production).

You can also define a rate limiter as a bean that implements the RateLimiter interface. In configuration, you can reference the bean by name using SpEL. #{@myRateLimiter} is a SpEL expression that references a bean with named myRateLimiter. The following listing defines a rate limiter that uses the KeyResolver defined in the previous listing:

Example 36. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: requestratelimiter_route
        uri: https://example.org
        filters:
        - name: RequestRateLimiter
          args:
            rate-limiter: "#{@myRateLimiter}"
            key-resolver: "#{@userKeyResolver}"

6.12. The RedirectTo GatewayFilter Factory

The RedirectTo GatewayFilter factory takes two parameters, status and url. The status parameter should be a 300 series redirect HTTP code, such as 301. The url parameter should be a valid URL. This is the value of the Location header. For relative redirects, you should use uri: no://op as the uri of your route definition. The following listing configures a RedirectTo GatewayFilter:

Example 37. 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.

6.13. The RemoveRequestHeader GatewayFilter Factory

The RemoveRequestHeader GatewayFilter factory takes a name parameter. It is the name of the header to be removed. The following listing configures a RemoveRequestHeader GatewayFilter:

Example 38. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: removerequestheader_route
        uri: https://example.org
        filters:
        - RemoveRequestHeader=X-Request-Foo

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

6.14. RemoveResponseHeader GatewayFilter Factory

The RemoveResponseHeader GatewayFilter factory takes a name parameter. It is the name of the header to be removed. The following listing configures a RemoveResponseHeader GatewayFilter:

Example 39. 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 for which you may want to do so. In addition, you can configure this filter once by using spring.cloud.gateway.default-filters and have it applied to all routes.

6.15. The RemoveRequestParameter GatewayFilter Factory

The RemoveRequestParameter GatewayFilter factory takes a name parameter. It is the name of the query parameter to be removed. The following example configures a RemoveRequestParameter GatewayFilter:

Example 40. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: removerequestparameter_route
        uri: https://example.org
        filters:
        - RemoveRequestParameter=red

This will remove the red parameter before it is sent downstream.

6.16. The RewritePath GatewayFilter Factory

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. The following listing configures a RewritePath GatewayFilter:

Example 41. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: rewritepath_route
        uri: https://example.org
        predicates:
        - Path=/red/**
        filters:
        - RewritePath=/red(?<segment>/?.*), $\{segment}

For a request path of /red/blue, this sets the path to /blue before making the downstream request. Note that the $ should be replaced with $\ because of the YAML specification.

6.17. RewriteLocationResponseHeader GatewayFilter Factory

The RewriteLocationResponseHeader GatewayFilter factory modifies the value of the Location response header, usually to get rid of backend-specific details. It takes stripVersionMode, locationHeaderName, hostValue, and protocolsRegex parameters. The following listing configures a RewriteLocationResponseHeader GatewayFilter:

Example 42. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: rewritelocationresponseheader_route
        uri: http://example.org
        filters:
        - RewriteLocationResponseHeader=AS_IN_REQUEST, Location, ,

For example, for a request of POST api.example.com/some/object/name, the Location response header value of object-service.prod.example.net/v2/some/object/id is rewritten as api.example.com/some/object/id.

The stripVersionMode parameter has the following possible values: NEVER_STRIP, AS_IN_REQUEST (default), and ALWAYS_STRIP.

  • NEVER_STRIP: The version is not stripped, even if the original request path contains no version.

  • AS_IN_REQUEST The version is stripped only if the original request path contains no version.

  • ALWAYS_STRIP The version is always stripped, even if the original request path contains version.

The hostValue parameter, if provided, is used to replace the host:port portion of the response Location header. If it is not provided, the value of the Host request header is used.

The protocolsRegex parameter must be a valid regex String, against which the protocol name is matched. If it is not matched, the filter does nothing. The default is http|https|ftp|ftps.

6.18. The RewriteResponseHeader GatewayFilter Factory

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. The following example configures a RewriteResponseHeader GatewayFilter:

Example 43. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: rewriteresponseheader_route
        uri: https://example.org
        filters:
        - RewriteResponseHeader=X-Response-Red, , password=[^&]+, password=***

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

6.19. The SaveSession GatewayFilter Factory

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 you need to ensure the session state has been saved before making the forwarded call. The following example configures a SaveSession GatewayFilter:

Example 44. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: save_session
        uri: https://example.org
        predicates:
        - Path=/foo/**
        filters:
        - SaveSession

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

6.20. The SecureHeaders GatewayFilter Factory

The SecureHeaders GatewayFilter factory adds a number of headers to the response, per the recommendation made in this blog post.

The following headers (shown with their default values) are added:

  • X-Xss-Protection:1 (mode=block)

  • Strict-Transport-Security (max-age=631138519)

  • X-Frame-Options (DENY)

  • X-Content-Type-Options (nosniff)

  • Referrer-Policy (no-referrer)

  • Content-Security-Policy (default-src 'self' https:; font-src 'self' https: data:; img-src 'self' https: data:; object-src 'none'; script-src https:; style-src 'self' https: 'unsafe-inline)'

  • X-Download-Options (noopen)

  • X-Permitted-Cross-Domain-Policies (none)

To change the default values, set the appropriate property in the spring.cloud.gateway.filter.secure-headers namespace. The following properties are available:

  • xss-protection-header

  • strict-transport-security

  • x-frame-options

  • x-content-type-options

  • referrer-policy

  • content-security-policy

  • x-download-options

  • x-permitted-cross-domain-policies

To disable the default values set the spring.cloud.gateway.filter.secure-headers.disable property with comma-separated values. The following example shows how to do so:

spring.cloud.gateway.filter.secure-headers.disable=x-frame-options,strict-transport-security
The lowercase full name of the secure header needs to be used to disable it..

6.21. The SetPath GatewayFilter Factory

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. The following example configures a SetPath GatewayFilter:

Example 45. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: setpath_route
        uri: https://example.org
        predicates:
        - Path=/red/{segment}
        filters:
        - SetPath=/{segment}

For a request path of /red/blue, this sets the path to /blue before making the downstream request.

6.22. The SetRequestHeader GatewayFilter Factory

The SetRequestHeader GatewayFilter factory takes name and value parameters. The following listing configures a SetRequestHeader GatewayFilter:

Example 46. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: setrequestheader_route
        uri: https://example.org
        filters:
        - SetRequestHeader=X-Request-Red, Blue

This GatewayFilter replaces (rather than adding) all headers with the given name. So, if the downstream server responded with a X-Request-Red:1234, this would be replaced with X-Request-Red:Blue, which is what the downstream service would receive.

SetRequestHeader is aware of URI variables used to match a path or host. URI variables may be used in the value and are expanded at runtime. The following example configures an SetRequestHeader GatewayFilter that uses a variable:

Example 47. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: setrequestheader_route
        uri: https://example.org
        predicates:
        - Host: {segment}.myhost.org
        filters:
        - SetRequestHeader=foo, bar-{segment}

6.23. The SetResponseHeader GatewayFilter Factory

The SetResponseHeader GatewayFilter factory takes name and value parameters. The following listing configures a SetResponseHeader GatewayFilter:

Example 48. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: setresponseheader_route
        uri: https://example.org
        filters:
        - SetResponseHeader=X-Response-Red, Blue

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

SetResponseHeader is aware of URI variables used to match a path or host. URI variables may be used in the value and will be expanded at runtime. The following example configures an SetResponseHeader GatewayFilter that uses a variable:

Example 49. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: setresponseheader_route
        uri: https://example.org
        predicates:
        - Host: {segment}.myhost.org
        filters:
        - SetResponseHeader=foo, bar-{segment}

6.24. The SetStatus GatewayFilter Factory

The SetStatus GatewayFilter factory takes a single parameter, status. It must be a valid Spring HttpStatus. It may be the integer value 404 or the string representation of the enumeration: NOT_FOUND. The following listing configures a SetStatus GatewayFilter:

Example 50. 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 is set to 401.

You can configure the SetStatus GatewayFilter to return the original HTTP status code from the proxied request in a header in the response. The header is added to the response if configured with the following property:

Example 51. application.yml
spring:
  cloud:
    gateway:
      set-status:
        original-status-header-name: original-http-status

6.25. The StripPrefix GatewayFilter Factory

The StripPrefix GatewayFilter factory takes one parameter, parts. The parts parameter indicates the number of parts in the path to strip from the request before sending it downstream. The following listing configures a StripPrefix GatewayFilter:

Example 52. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: nameRoot
        uri: https://nameservice
        predicates:
        - Path=/name/**
        filters:
        - StripPrefix=2

When a request is made through the gateway to /name/blue/red, the request made to nameservice looks like nameservice/red.

6.26. The Retry GatewayFilter Factory

The Retry GatewayFilter factory supports the following parameters:

  • retries: The number of retries that should be attempted.

  • statuses: The HTTP status codes that should be retried, represented by using org.springframework.http.HttpStatus.

  • methods: The HTTP methods that should be retried, represented by using org.springframework.http.HttpMethod.

  • series: The series of status codes to be retried, represented by using org.springframework.http.HttpStatus.Series.

  • exceptions: A list of thrown exceptions that should be retried.

  • backoff: The configured exponential backoff for the retries. Retries are performed after a backoff interval of firstBackoff * (factor ^ n), where n is the iteration. If maxBackoff is configured, the maximum backoff applied is limited to maxBackoff. If basedOnPreviousValue is true, the backoff is calculated byusing prevBackoff * factor.

The following defaults are configured for Retry filter, if enabled:

  • retries: Three times

  • series: 5XX series

  • methods: GET method

  • exceptions: IOException and TimeoutException

  • backoff: disabled

The following listing configures a Retry GatewayFilter:

Example 53. 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
            methods: GET,POST
            backoff:
              firstBackoff: 10ms
              maxBackoff: 50ms
              factor: 2
              basedOnPreviousValue: false
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 (for example, through a Mono.error(ex) return value), which the retry filter can be configured to handle by retrying.
When using the retry filter with any HTTP method with a body, the body will be cached and the gateway will become memory constrained. The body is cached in a request attribute defined by ServerWebExchangeUtils.CACHED_REQUEST_BODY_ATTR. The type of the object is a org.springframework.core.io.buffer.DataBuffer.

6.27. The RequestSize GatewayFilter Factory

When the request size is greater than the permissible limit, the RequestSize GatewayFilter factory can restrict a request from reaching the downstream service. The filter takes a maxSize parameter. The maxSize is a `DataSize type, so values can be defined as a number followed by an optional DataUnit suffix such as 'KB' or 'MB'. The default is 'B' for bytes. It is the permissible size limit of the request defined in bytes. The following listing configures a RequestSize GatewayFilter:

Example 54. 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 sets the response status as 413 Payload Too Large with an additional header errorMessage when the request is rejected due to size. The following example shows such an errorMessage:

errorMessage` : `Request size is larger than permissible limit. Request size is 6.0 MB where permissible limit is 5.0 MB
The default request size is set to five MB if not provided as a filter argument in the route definition.

6.28. The SetRequestHost GatewayFilter Factory

There are certain situation when the host header may need to be overridden. In this situation, the SetRequestHost GatewayFilter factory can replace the existing host header with a specified vaue. The filter takes a host parameter. The following listing configures a SetRequestHost GatewayFilter:

Example 55. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: set_request_host_header_route
        uri: http://localhost:8080/headers
        predicates:
        - Path=/headers
        filters:
        - name: SetRequestHost
          args:
            host: example.org

The SetRequestHost GatewayFilter factory replaces the value of the host header with example.org.

6.29. Modify a Request Body GatewayFilter Factory

You can use the ModifyRequestBody filter filter to modify the request body before it is sent downstream by the gateway.

This filter can be configured only by using the Java DSL.

The following listing shows how to modify a request body GatewayFilter:

@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;
    }
}

6.30. Modify a Response Body GatewayFilter Factory

You can use the ModifyResponseBody filter to modify the response body before it is sent back to the client.

This filter can be configured only by using the Java DSL.

The following listing shows how to modify a response body GatewayFilter:

@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();
}

6.31. Default Filters

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. The following listing defines a set of default filters:

Example 56. application.yml
spring:
  cloud:
    gateway:
      default-filters:
      - AddResponseHeader=X-Response-Default-Red, Default-Blue
      - PrefixPath=/httpbin

7. Global Filters

The GlobalFilter interface has the same signature as GatewayFilter. These are special filters that are conditionally applied to all routes.

This interface and its usage are subject to change in future milestone releases.

7.1. Combined Global Filter and GatewayFilter Ordering

When a request matches a route, the filtering web handler adds all instances of GlobalFilter and all route-specific instances of GatewayFilter to a filter chain. This combined filter chain is sorted by the org.springframework.core.Ordered interface, which you can set by implementing the getOrder() method.

As Spring Cloud Gateway distinguishes between “pre” and “post” phases for filter logic execution (see How it Works), the filter with the highest precedence is the first in the “pre”-phase and the last in the “post”-phase.

The following listing configures a filter chain:

Example 57. ExampleConfiguration.java
@Bean
public GlobalFilter customFilter() {
    return new CustomGlobalFilter();
}

public class CustomGlobalFilter implements GlobalFilter, Ordered {

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        log.info("custom global filter");
        return chain.filter(exchange);
    }

    @Override
    public int getOrder() {
        return -1;
    }
}

7.2. Forward Routing Filter

The ForwardRoutingFilter looks for a URI in the exchange attribute ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR. If the URL has a forward scheme (such as forward:///localendpoint), it uses the Spring DispatcherHandler to handle the request. The path part of the request URL is overridden with the path in the forward URL. The unmodified original URL is appended to the list in the ServerWebExchangeUtils.GATEWAY_ORIGINAL_REQUEST_URL_ATTR attribute.

7.3. The LoadBalancerClient Filter

The LoadBalancerClientFilter looks for a URI in the exchange attribute named ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR. If the URL has a scheme of lb (such as lb://myservice), it uses the Spring Cloud LoadBalancerClient to resolve the name (myservice in this case) to an actual host and port and replaces the URI in the same attribute. The unmodified original URL is appended to the list in the ServerWebExchangeUtils.GATEWAY_ORIGINAL_REQUEST_URL_ATTR attribute. The filter also looks in the ServerWebExchangeUtils.GATEWAY_SCHEME_PREFIX_ATTR attribute to see if it equals lb. If so, the same rules apply. The following listing configures a LoadBalancerClientFilter:

Example 58. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: myRoute
        uri: lb://service
        predicates:
        - Path=/service/**
By default, when a service instance cannot be found in the LoadBalancer, a 503 is returned. You can configure the Gateway to return a 404 by setting spring.cloud.gateway.loadbalancer.use404=true.
The isSecure value of the ServiceInstance returned from the LoadBalancer overrides the scheme specified in the request made to the Gateway. For example, if the request comes into the Gateway over HTTPS but the ServiceInstance indicates it is not secure, the downstream request is made over HTTP. The opposite situation can also apply. However, if GATEWAY_SCHEME_PREFIX_ATTR is specified for the route in the Gateway configuration, the prefix is stripped and the resulting scheme from the route URL overrides the ServiceInstance configuration.
LoadBalancerClientFilter uses a blocking ribbon LoadBalancerClient under the hood. We suggest you use ReactiveLoadBalancerClientFilter instead. You can switch to it by setting the value of the spring.cloud.loadbalancer.ribbon.enabled to false.

7.4. The ReactiveLoadBalancerClientFilter

The ReactiveLoadBalancerClientFilter looks for a URI in the exchange attribute named ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR. If the URL has a lb scheme (such as lb://myservice), it uses the Spring Cloud ReactorLoadBalancer to resolve the name (myservice in this example) to an actual host and port and replaces the URI in the same attribute. The unmodified original URL is appended to the list in the ServerWebExchangeUtils.GATEWAY_ORIGINAL_REQUEST_URL_ATTR attribute. The filter also looks in the ServerWebExchangeUtils.GATEWAY_SCHEME_PREFIX_ATTR attribute to see if it equals lb. If so, the same rules apply. The following listing configures a ReactiveLoadBalancerClientFilter:

Example 59. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: myRoute
        uri: lb://service
        predicates:
        - Path=/service/**
By default, when a service instance cannot be found by the ReactorLoadBalancer, a 503 is returned. You can configure the gateway to return a 404 by setting spring.cloud.gateway.loadbalancer.use404=true.
The isSecure value of the ServiceInstance returned from the ReactiveLoadBalancerClientFilter overrides the scheme specified in the request made to the Gateway. For example, if the request comes into the Gateway over HTTPS but the ServiceInstance indicates it is not secure, the downstream request is made over HTTP. The opposite situation can also apply. However, if GATEWAY_SCHEME_PREFIX_ATTR is specified for the route in the Gateway configuration, the prefix is stripped and the resulting scheme from the route URL overrides the ServiceInstance configuration.

7.5. The Netty Routing Filter

The Netty routing filter runs if the URL located in the ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR exchange attribute has a http or https scheme. It uses the Netty HttpClient to make the downstream proxy request. The response is put in the ServerWebExchangeUtils.CLIENT_RESPONSE_ATTR exchange attribute for use in a later filter. (There is also an experimental WebClientHttpRoutingFilter that performs the same function but does not require Netty.)

7.6. The Netty Write Response Filter

The NettyWriteResponseFilter runs if there is a Netty HttpClientResponse in the ServerWebExchangeUtils.CLIENT_RESPONSE_ATTR exchange attribute. It runs after all other filters have completed and writes the proxy response back to the gateway client response. (There is also an experimental WebClientWriteResponseFilter that performs the same function but does not require Netty.)

7.7. The RouteToRequestUrl Filter

If there is a Route object in the ServerWebExchangeUtils.GATEWAY_ROUTE_ATTR exchange attribute, the RouteToRequestUrlFilter runs. It creates a new URI, based off of the request URI but updated with the URI attribute of the Route object. The new URI is placed in the ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR exchange attribute`.

If the URI has a scheme prefix, such as lb:ws://serviceid, the lb scheme is stripped from the URI and placed in the ServerWebExchangeUtils.GATEWAY_SCHEME_PREFIX_ATTR for use later in the filter chain.

7.8. The Websocket Routing Filter

If the URL located in the ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR exchange attribute has a ws or wss scheme, the websocket routing filter runs. It uses the Spring WebSocket infrastructure to forward the websocket request downstream.

You can load-balance websockets by prefixing the URI with lb, such as lb:ws://serviceid.

If you use SockJS as a fallback over normal HTTP, you should configure a normal HTTP route as well as the websocket Route.

The following listing configures a websocket routing filter:

Example 60. application.yml
spring:
  cloud:
    gateway:
      routes:
      # SockJS route
      - id: websocket_sockjs_route
        uri: http://localhost:3001
        predicates:
        - Path=/websocket/info/**
      # Normal Websocket route
      - id: websocket_route
        uri: ws://localhost:3001
        predicates:
        - Path=/websocket/**

7.9. The Gateway Metrics Filter

To enable gateway metrics, add spring-boot-starter-actuator as a project dependency. Then, by default, the gateway metrics filter runs as long as the property spring.cloud.gateway.metrics.enabled is not set to false. This filter adds a timer metric named gateway.requests with the following tags:

  • routeId: The route ID.

  • routeUri: The URI to which the API is routed.

  • outcome: The outcome, as classified by HttpStatus.Series.

  • status: The HTTP status of the request returned to the client.

  • httpStatusCode: The HTTP Status of the request returned to the client.

  • httpMethod: The HTTP method used for the request.

These metrics are then available to be scraped from /actuator/metrics/gateway.requests and can be easily integrated with Prometheus to create a Grafana dashboard.

To enable the prometheus endpoint, add micrometer-registry-prometheus as a project dependency.

7.10. Marking An Exchange As Routed

After the gateway has routed a ServerWebExchange, it marks that exchange as “routed” by adding gatewayAlreadyRouted to the exchange attributes. Once a request has been marked as routed, other routing filters will not route the request again, essentially skipping the filter. There are convenience methods that you can use to mark an exchange as routed or check if an exchange has already been routed.

  • ServerWebExchangeUtils.isAlreadyRouted takes a ServerWebExchange object and checks if it has been “routed”.

  • ServerWebExchangeUtils.setAlreadyRouted takes a ServerWebExchange object and marks it as “routed”.

8. HttpHeadersFilters

HttpHeadersFilters are applied to requests before sending them downstream, such as in the NettyRoutingFilter.

8.1. Forwarded Headers Filter

The Forwarded Headers Filter creates a Forwarded header to send to the downstream service. It adds the Host header, scheme and port of the current request to any existing Forwarded header.

8.2. RemoveHopByHop Headers Filter

The RemoveHopByHop Headers Filter removes headers from forwarded requests. The default list of headers that is removed comes from the IETF.

The default removed headers are:
  • Connection

  • Keep-Alive

  • Proxy-Authenticate

  • Proxy-Authorization

  • TE

  • Trailer

  • Transfer-Encoding

  • Upgrade

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

8.3. XForwarded Headers Filter

The XForwarded Headers Filter creates various a X-Forwarded-* headers to send to the downstream service. It users the Host header, scheme, port and path of the current request to create the various headers.

Creating of individual headers can be controlled by the following boolean properties (defaults to true):

  • spring.cloud.gateway.x-forwarded.for-enabled

  • spring.cloud.gateway.x-forwarded.host-enabled

  • spring.cloud.gateway.x-forwarded.port-enabled

  • spring.cloud.gateway.x-forwarded.proto-enabled

  • spring.cloud.gateway.x-forwarded.prefix-enabled

Appending multiple headers can be controlled by the following boolean properties (defaults to true):

  • spring.cloud.gateway.x-forwarded.for-append

  • spring.cloud.gateway.x-forwarded.host-append

  • spring.cloud.gateway.x-forwarded.port-append

  • spring.cloud.gateway.x-forwarded.proto-append

  • spring.cloud.gateway.x-forwarded.prefix-append

9. TLS and SSL

The gateway can listen for requests on HTTPS by following the usual Spring server configuration. The following example shows how to do so:

Example 61. application.yml
server:
  ssl:
    enabled: true
    key-alias: scg
    key-store-password: scg1234
    key-store: classpath:scg-keystore.p12
    key-store-type: PKCS12

You can route gateway routes to both HTTP and HTTPS backends. If you are routing to an HTTPS backend, you can configure the gateway to trust all downstream certificates with the following configuration:

Example 62. application.yml
spring:
  cloud:
    gateway:
      httpclient:
        ssl:
          useInsecureTrustManager: true

Using an insecure trust manager is not suitable for production. For a production deployment, you can configure the gateway with a set of known certificates that it can trust with the following configuration:

Example 63. application.yml
spring:
  cloud:
    gateway:
      httpclient:
        ssl:
          trustedX509Certificates:
          - cert1.pem
          - cert2.pem

If the Spring Cloud Gateway is not provisioned with trusted certificates, the default trust store is used (which you can override by setting the javax.net.ssl.trustStore system property).

9.1. TLS Handshake

The gateway maintains a client pool that it uses to route to backends. When communicating over HTTPS, the client initiates a TLS handshake. A number of timeouts are associated with this handshake. You can configure these timeouts can be configured (defaults shown) as follows:

Example 64. application.yml
spring:
  cloud:
    gateway:
      httpclient:
        ssl:
          handshake-timeout-millis: 10000
          close-notify-flush-timeout-millis: 3000
          close-notify-read-timeout-millis: 0

10. Configuration

Configuration for Spring Cloud Gateway is driven by a collection of RouteDefinitionLocator instances. The following listing shows the definition of the RouteDefinitionLocator interface:

Example 65. RouteDefinitionLocator.java
public interface RouteDefinitionLocator {
    Flux<RouteDefinition> getRouteDefinitions();
}

By default, a PropertiesRouteDefinitionLocator loads properties by using Spring Boot’s @ConfigurationProperties mechanism.

The earlier configuration examples all use a shortcut notation that uses positional arguments rather than named ones. The following two examples are equivalent:

Example 66. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: setstatus_route
        uri: https://example.org
        filters:
        - name: SetStatus
          args:
            status: 401
      - id: setstatusshortcut_route
        uri: https://example.org
        filters:
        - SetStatus=401

For some usages of the gateway, properties are adequate, but some production use cases benefit from loading configuration from an external source, such as a database. Future milestone versions will have RouteDefinitionLocator implementations based off of Spring Data Repositories, such as Redis, MongoDB, and Cassandra.

11. Route Metadata Configuration

You can configure additional parameters for each route by using metadata, as follows:

Example 67. application.yml
spring:
  cloud:
    gateway:
      routes:
      - id: route_with_metadata
        uri: https://example.org
        metadata:
          optionName: "OptionValue"
          compositeObject:
            name: "value"
          iAmNumber: 1

You could acquire all metadata properties from an exchange, as follows:

Route route = exchange.getAttribute(GATEWAY_ROUTE_ATTR);
// get all metadata properties
route.getMetadata();
// get a single metadata property
route.getMetadata(someKey);

12. Http timeouts configuration

Http timeouts (response and connect) can be configured for all routes and overridden for each specific route.

12.1. Global timeouts

To configure Global http timeouts:
connect-timeout must be specified in milliseconds.
response-timeout must be specified as a java.time.Duration

global http timeouts example
spring:
  cloud:
    gateway:
      httpclient:
        connect-timeout: 1000
        response-timeout: 5s

12.2. Per-route timeouts

To configure per-route timeouts:
connect-timeout must be specified in milliseconds.
response-timeout must be specified in milliseconds.

per-route http timeouts configuration via configuration
      - id: per_route_timeouts
        uri: https://example.org
        predicates:
          - name: Path
            args:
              pattern: /delay/{timeout}
        metadata:
          response-timeout: 200
          connect-timeout: 200
per-route timeouts configuration using Java DSL
import static org.springframework.cloud.gateway.support.RouteMetadataUtils.CONNECT_TIMEOUT_ATTR;
import static org.springframework.cloud.gateway.support.RouteMetadataUtils.RESPONSE_TIMEOUT_ATTR;

      @Bean
      public RouteLocator customRouteLocator(RouteLocatorBuilder routeBuilder){
         return routeBuilder.routes()
               .route("test1", r -> {
                  return r.host("*.somehost.org").and().path("/somepath")
                        .filters(f -> f.addRequestHeader("header1", "header-value-1"))
                        .uri("http://someuri")
                        .metadata(RESPONSE_TIMEOUT_ATTR, 200)
                        .metadata(CONNECT_TIMEOUT_ATTR, 200);
               })
               .build();
      }

12.3. Fluent Java Routes API

To allow for simple configuration in Java, the RouteLocatorBuilder bean includes a fluent API. The following listing shows how it works:

Example 68. GatewaySampleApplication.java
// static imports from GatewayFilters and RoutePredicates
@Bean
public RouteLocator customRouteLocator(RouteLocatorBuilder builder, ThrottleGatewayFilterFactory throttle) {
    return builder.routes()
            .route(r -> r.host("**.abc.org").and().path("/image/png")
                .filters(f ->
                        f.addResponseHeader("X-TestHeader", "foobar"))
                .uri("http://httpbin.org:80")
            )
            .route(r -> r.path("/image/webp")
                .filters(f ->
                        f.addResponseHeader("X-AnotherHeader", "baz"))
                .uri("http://httpbin.org:80")
                .metadata("key", "value")
            )
            .route(r -> r.order(-1)
                .host("**.throttle.org").and().path("/get")
                .filters(f -> f.filter(throttle.apply(1,
                        1,
                        10,
                        TimeUnit.SECONDS)))
                .uri("http://httpbin.org:80")
                .metadata("key", "value")
            )
            .build();
}

This style also allows for more custom predicate assertions. The predicates defined by RouteDefinitionLocator beans are combined using logical and. By using the fluent Java API, you can use the and(), or(), and negate() operators on the Predicate class.

12.4. The DiscoveryClient Route Definition Locator

You can configure the gateway to create routes based on services registered with a DiscoveryClient compatible service registry.

To enable this, set spring.cloud.gateway.discovery.locator.enabled=true and make sure a DiscoveryClient implementation (such as Netflix Eureka, Consul, or Zookeeper) is on the classpath and enabled.

12.4.1. Configuring Predicates and Filters For DiscoveryClient Routes

By default, the gateway defines a single predicate and filter for routes created with a DiscoveryClient.

The default predicate is a path predicate defined with the pattern /serviceId/**, where serviceId is the ID of the service from the DiscoveryClient.

The default filter is a rewrite path filter with the regex /serviceId/(?<remaining>.*) and the replacement /${remaining}. This strips the service ID from the path before the request is sent downstream.

If you want to customize the predicates or filters used by the DiscoveryClient routes, set spring.cloud.gateway.discovery.locator.predicates[x] and spring.cloud.gateway.discovery.locator.filters[y]. When doing so, you need to make sure to include the default predicate and filter shown earlier, if you want to retain that functionality. The following example shows what this looks like:

Example 69. application.properties
spring.cloud.gateway.discovery.locator.predicates[0].name: Path
spring.cloud.gateway.discovery.locator.predicates[0].args[pattern]: "'/'+serviceId+'/**'"
spring.cloud.gateway.discovery.locator.predicates[1].name: Host
spring.cloud.gateway.discovery.locator.predicates[1].args[pattern]: "'**.foo.com'"
spring.cloud.gateway.discovery.locator.filters[0].name: Hystrix
spring.cloud.gateway.discovery.locator.filters[0].args[name]: serviceId
spring.cloud.gateway.discovery.locator.filters[1].name: RewritePath
spring.cloud.gateway.discovery.locator.filters[1].args[regexp]: "'/' + serviceId + '/(?<remaining>.*)'"
spring.cloud.gateway.discovery.locator.filters[1].args[replacement]: "'/${remaining}'"

13. Reactor Netty Access Logs

To enable Reactor Netty access logs, set -Dreactor.netty.http.server.accessLogEnabled=true.

It must be a Java System Property, not a Spring Boot property.

You can configure the logging system to have a separate access log file. The following example creates a Logback configuration:

Example 70. logback.xml
    <appender name="accessLog" class="ch.qos.logback.core.FileAppender">
        <file>access_log.log</file>
        <encoder>
            <pattern>%msg%n</pattern>
        </encoder>
    </appender>
    <appender name="async" class="ch.qos.logback.classic.AsyncAppender">
        <appender-ref ref="accessLog" />
    </appender>

    <logger name="reactor.netty.http.server.AccessLog" level="INFO" additivity="false">
        <appender-ref ref="async"/>
    </logger>

14. CORS Configuration

You can configure the gateway to control CORS behavior. The “global” CORS configuration is a map of URL patterns to Spring Framework CorsConfiguration. The following example configures CORS:

Example 71. application.yml
spring:
  cloud:
    gateway:
      globalcors:
        cors-configurations:
          '[/**]':
            allowedOrigins: "https://docs.spring.io"
            allowedMethods:
            - GET

In the preceding example, CORS requests are allowed from requests that originate from docs.spring.io for all GET requested paths.

To provide the same CORS configuration to requests that are not handled by some gateway route predicate, set the spring.cloud.gateway.globalcors.add-to-simple-url-handler-mapping property to true. This is useful when you try to support CORS preflight requests and your route predicate does not evalute to true because the HTTP method is options.

15. Actuator API

The /gateway actuator endpoint lets you monitor and interact with a Spring Cloud Gateway application. To be remotely accessible, the endpoint has to be enabled and exposed over HTTP or JMX in the application properties. The following listing shows how to do so:

Example 72. application.properties
management.endpoint.gateway.enabled=true # default value
management.endpoints.web.exposure.include=gateway

15.1. Verbose Actuator Format

A new, more verbose format has been added to Spring Cloud Gateway. It adds more detail to each route, letting you view the predicates and filters associated with each route along with any configuration that is available. The following example configures /actuator/gateway/routes:

[
  {
    "predicate": "(Hosts: [**.addrequestheader.org] && Paths: [/headers], match trailing slash: true)",
    "route_id": "add_request_header_test",
    "filters": [
      "[[AddResponseHeader X-Response-Default-Foo = 'Default-Bar'], order = 1]",
      "[[AddRequestHeader X-Request-Foo = 'Bar'], order = 1]",
      "[[PrefixPath prefix = '/httpbin'], order = 2]"
    ],
    "uri": "lb://testservice",
    "order": 0
  }
]

This feature is enabled by default. To disable it, set the following property:

Example 73. application.properties
spring.cloud.gateway.actuator.verbose.enabled=false

This will default to true in a future release.

15.2. Retrieving Route Filters

This section details how to retrieve route filters, including:

15.2.1. Global Filters

To retrieve the global filters applied to all routes, make a GET request to /actuator/gateway/globalfilters. The resulting response is similar to the following:

{
  "or[email protected]77856cc5": 10100,
  "org.springframework.cloud.gateway.filter.RouteToRequestU[email protected]": 10000,
  "or[email protected]32d22650": -1,
  "[email protected]6459d9": 2147483647,
  "[email protected]5e0": 2147483647,
  "[email protected]d23": 0,
  "org.s[email protected]135064ea": 2147483637,
  "[email protected]23c05889": 2147483646
}

The response contains the details of the global filters that are in place. For each global filter, there is a string representation of the filter object (for example, or[email protected]77856cc5) and the corresponding order in the filter chain.}

15.2.2. Route Filters

To retrieve the GatewayFilter factories applied to routes, make a GET request to /actuator/gateway/routefilters. The resulting response is similar to the following:

{
  "[[email protected] configClass = AbstractNameValueGatewayFilterFactory.NameValueConfig]": null,
  "[[email protected] configClass = Object]": null,
  "[[email protected] configClass = Object]": null
}

The response contains the details of the GatewayFilter factories applied to any particular route. For each factory there is a string representation of the corresponding object (for example, [[email protected] configClass = Object]). Note that the null value is due to an incomplete implementation of the endpoint controller, because it tries to set the order of the object in the filter chain, which does not apply to a GatewayFilter factory object.

15.3. Refreshing the Route Cache

To clear the routes cache, make a POST request to /actuator/gateway/refresh. The request returns a 200 without a response body.

15.4. Retrieving the Routes Defined in the Gateway

To retrieve the routes defined in the gateway, make a GET request to /actuator/gateway/routes. The resulting response is similar to the following:

[{
  "route_id": "first_route",
  "route_object": {
    "predicate": "org.springframework.cloud.gateway.handler.predicate.PathRoutePredicateFactory$$Lambda$432/[email protected]",
    "filters": [
      "OrderedGatewayFilter{delegate=org.springframework.cloud.gateway.filter.factory.PreserveHostHeaderGatewayFilterFactory$$Lambda$436/[email protected], order=0}"
    ]
  },
  "order": 0
},
{
  "route_id": "second_route",
  "route_object": {
    "predicate": "org.springframework.cloud.gateway.handler.predicate.PathRoutePredicateFactory$$Lambda$432/[email protected]",
    "filters": []
  },
  "order": 0
}]

The response contains the details of all the routes defined in the gateway. The following table describes the structure of each element (each is a route) of the response:

Path Type Description

route_id

String

The route ID.

route_object.predicate

Object

The route predicate.

route_object.filters

Array

The GatewayFilter factories applied to the route.

order

Number

The route order.

15.5. Retrieving Information about a Particular Route

To retrieve information about a single route, make a GET request to /actuator/gateway/routes/{id} (for example, /actuator/gateway/routes/first_route). The resulting response is similar to the following:

{
  "id": "first_route",
  "predicates": [{
    "name": "Path",
    "args": {"_genkey_0":"/first"}
  }],
  "filters": [],
  "uri": "https://www.uri-destination.org",
  "order": 0
}]

The following table describes the structure of the response:

Path Type Description

id

String

The route ID.

predicates

Array

The collection of route predicates. Each item defines the name and the arguments of a given predicate.

filters

Array

The collection of filters applied to the route.

uri

String

The destination URI of the route.

order

Number

The route order.

15.6. Creating and Deleting a Particular Route

To create a route, make a POST request to /gateway/routes/{id_route_to_create} with a JSON body that specifies the fields of the route (see Retrieving Information about a Particular Route).

To delete a route, make a DELETE request to /gateway/routes/{id_route_to_delete}.

15.7. Recap: The List of All endpoints

The folloiwng table below summarizes the Spring Cloud Gateway actuator endpoints (note that each endpoint has /actuator/gateway as the base-path):

ID HTTP Method Description

globalfilters

GET

Displays the list of global filters applied to the routes.

routefilters

GET

Displays the list of GatewayFilter factories applied to a particular route.

refresh

POST

Clears the routes cache.

routes

GET

Displays the list of routes defined in the gateway.

routes/{id}

GET

Displays information about a particular route.

routes/{id}

POST

Adds a new route to the gateway.

routes/{id}

DELETE

Removes an existing route from the gateway.

16. Troubleshooting

This section covers common problems that may arise when you use Spring Cloud Gateway.

16.1. Log Levels

The following loggers may contain valuable troubleshooting information at the DEBUG and TRACE levels:

  • org.springframework.cloud.gateway

  • org.springframework.http.server.reactive

  • org.springframework.web.reactive

  • org.springframework.boot.autoconfigure.web

  • reactor.netty

  • redisratelimiter

16.2. Wiretap

The Reactor Netty HttpClient and HttpServer can have wiretap enabled. When combined with setting the reactor.netty log level to DEBUG or TRACE, it enables the logging of information, such as headers and bodies sent and received across the wire. To enable wiretap, set spring.cloud.gateway.httpserver.wiretap=true or spring.cloud.gateway.httpclient.wiretap=true for the HttpServer and HttpClient, respectively.

17. Developer Guide

These are basic guides to writing some custom components of the gateway.

17.1. Writing Custom Route Predicate Factories

In order to write a Route Predicate you will need to implement RoutePredicateFactory. There is an abstract class called AbstractRoutePredicateFactory which you can extend.

MyRoutePredicateFactory.java
public class MyRoutePredicateFactory extends AbstractRoutePredicateFactory<HeaderRoutePredicateFactory.Config> {

    public MyRoutePredicateFactory() {
        super(Config.class);
    }

    @Override
    public Predicate<ServerWebExchange> apply(Config config) {
        // grab configuration from Config object
        return exchange -> {
            //grab the request
            ServerHttpRequest request = exchange.getRequest();
            //take information from the request to see if it
            //matches configuration.
            return matches(config, request);
        };
    }

    public static class Config {
        //Put the configuration properties for your filter here
    }

}

17.2. Writing Custom GatewayFilter Factories

To write a GatewayFilter, you must implement GatewayFilterFactory. You can extend an abstract class called AbstractGatewayFilterFactory. The following examples show how to do so:

Example 74. PreGatewayFilterFactory.java
public class PreGatewayFilterFactory extends AbstractGatewayFilterFactory<PreGatewayFilterFactory.Config> {

    public PreGatewayFilterFactory() {
        super(Config.class);
    }

    @Override
    public GatewayFilter apply(Config config) {
        // grab configuration from Config object
        return (exchange, chain) -> {
            //If you want to build a "pre" filter you need to manipulate the
            //request before calling chain.filter
            ServerHttpRequest.Builder builder = exchange.getRequest().mutate();
            //use builder to manipulate the request
            return chain.filter(exchange.mutate().request(builder.build()).build());
        };
    }

    public static class Config {
        //Put the configuration properties for your filter here
    }

}
PostGatewayFilterFactory.java
public class PostGatewayFilterFactory extends AbstractGatewayFilterFactory<PostGatewayFilterFactory.Config> {

    public PostGatewayFilterFactory() {
        super(Config.class);
    }

    @Override
    public GatewayFilter apply(Config config) {
        // grab configuration from Config object
        return (exchange, chain) -> {
            return chain.filter(exchange).then(Mono.fromRunnable(() -> {
                ServerHttpResponse response = exchange.getResponse();
                //Manipulate the response in some way
            }));
        };
    }

    public static class Config {
        //Put the configuration properties for your filter here
    }

}

17.2.1. Naming Custom Filters And References In Configuration

Custom filters class names should end in GatewayFilterFactory.

For example, to reference a filter named Something in configuration files, the filter must be in a class named SomethingGatewayFilterFactory.

It is possible to create a gateway filter named without the GatewayFilterFactory suffix, such as class AnotherThing. This filter could be referenced as AnotherThing in configuration files. This is not a supported naming convention and this syntax may be removed in future releases. Please update the filter name to be compliant.

17.3. Writing Custom Global Filters

To write a custom global filter, you must implement GlobalFilter interface. This applies the filter to all requests.

The following examples show how to set up global pre and post filters, respectively:

@Bean
public GlobalFilter customGlobalFilter() {
    return (exchange, chain) -> exchange.getPrincipal()
        .map(Principal::getName)
        .defaultIfEmpty("Default User")
        .map(userName -> {
          //adds header to proxied request
          exchange.getRequest().mutate().header("CUSTOM-REQUEST-HEADER", userName).build();
          return exchange;
        })
        .flatMap(chain::filter);
}

@Bean
public GlobalFilter customGlobalPostFilter() {
    return (exchange, chain) -> chain.filter(exchange)
        .then(Mono.just(exchange))
        .map(serverWebExchange -> {
          //adds header to response
          serverWebExchange.getResponse().getHeaders().set("CUSTOM-RESPONSE-HEADER",
              HttpStatus.OK.equals(serverWebExchange.getResponse().getStatusCode()) ? "It worked": "It did not work");
          return serverWebExchange;
        })
        .then();
}

18. Building a Simple Gateway by Using Spring MVC or Webflux

The following describes an alternative style gateway. None of the prior documentation applies to what follows.

Spring Cloud Gateway provides a utility object called ProxyExchange. You can use it inside a regular Spring web handler as a method parameter. It supports basic downstream HTTP exchanges through methods that mirror the HTTP verbs. With MVC, it also supports forwarding to a local handler through the forward() method. To use the ProxyExchange, include the right module in your classpath (either spring-cloud-gateway-mvc or spring-cloud-gateway-webflux).

The following MVC example proxies a request to /test downstream to a remote server:

@RestController
@SpringBootApplication
public class GatewaySampleApplication {

    @Value("${remote.home}")
    private URI home;

    @GetMapping("/test")
    public ResponseEntity<?> proxy(ProxyExchange<byte[]> proxy) throws Exception {
        return proxy.uri(home.toString() + "/image/png").get();
    }

}

The following example does the same thing with Webflux:

@RestController
@SpringBootApplication
public class GatewaySampleApplication {

    @Value("${remote.home}")
    private URI home;

    @GetMapping("/test")
    public Mono<ResponseEntity<?>> proxy(ProxyExchange<byte[]> proxy) throws Exception {
        return proxy.uri(home.toString() + "/image/png").get();
    }

}

Convenience methods on the ProxyExchange enable the handler method to discover and enhance the URI path of the incoming request. For example, you might want to extract the trailing elements of a path to pass them downstream:

@GetMapping("/proxy/path/**")
public ResponseEntity<?> proxyPath(ProxyExchange<byte[]> proxy) throws Exception {
  String path = proxy.path("/proxy/path/");
  return proxy.uri(home.toString() + "/foos/" + path).get();
}

All the features of Spring MVC and Webflux are available to gateway handler methods. As a result, you can inject request headers and query parameters, for instance, and you can constrain the incoming requests with declarations in the mapping annotation. See the documentation for @RequestMapping in Spring MVC for more details of those features.

You can add headers to the downstream response by using the header() methods on ProxyExchange.

You can also manipulate response headers (and anything else you like in the response) by adding a mapper to the get() method (and other methods). The mapper is a Function that takes the incoming ResponseEntity and converts it to an outgoing one.

First-class support is provided for “sensitive” headers (by default, cookie and authorization), which are not passed downstream, and for “proxy” (x-forwarded-*) headers.

19. Configuration properties

To see the list of all Spring Cloud Gateway related configuration properties, see the appendix.