Spring Cloud Gateway

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

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

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.

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

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:

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

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:

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

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:

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:

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

The Header route predicate factory takes two parameters, the header 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:

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).

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:

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

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:

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

The Path Route Predicate Factory takes two parameters: a list of Spring PathMatcher patterns and an optional flag called matchTrailingSlash (defaults to true). The following example configures a path route predicate:

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

If matchTrailingSlash is set to false, then request path /red/1/ will not be matched.

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:

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:

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

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

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:

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

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:

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

The XForwarded Remote Addr 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).

This route predicate allows requests to be filtered based on the X-Forwarded-For HTTP header.

This can be used with reverse proxies such as load balancers or web application firewalls where the request should only be allowed if it comes from a trusted list of IP addresses used by those reverse proxies.

The following example configures a XForwardedRemoteAddr route predicate:

This route matches if the X-Forwarded-For header contains, for example, 192.168.1.10.

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

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:

The AddRequestHeadersIfNotPresent GatewayFilter factory takes a collection of name and value pairs separated by colon. The following example configures an AddRequestHeadersIfNotPresent GatewayFilter:

This listing adds 2 headers X-Request-Color-1:blue and X-Request-Color-2:green to the downstream request’s headers for all matching requests. This is similar to how AddRequestHeader works, but unlike AddRequestHeader it will do it only if the header is not already there. Otherwise, the original value in the client request is sent.

Additionally, to set a multi-valued header, use the header name multiple times like AddRequestHeadersIfNotPresent=X-Request-Color-1:blue,X-Request-Color-1:green.

AddRequestHeadersIfNotPresent also supports 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 AddRequestHeadersIfNotPresent GatewayFilter that uses a variable:

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

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:

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

This adds X-Response-Red:Blue 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:

The Spring Cloud CircuitBreaker GatewayFilter factory uses the Spring Cloud CircuitBreaker APIs to wrap Gateway routes in a circuit breaker. Spring Cloud CircuitBreaker supports multiple libraries that can be used with Spring Cloud Gateway. Spring Cloud supports Resilience4J out of the box.

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

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:

The following listing does the same thing in Java:

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

CircuitBreaker also supports URI variables in the fallbackUri. This allows more complex routing options, like forwarding sections of the original host or url path using PathPattern expression.

In the example below the call consumingServiceEndpoint/users/1 will be redirected to inCaseOfFailureUseThis/users/1.

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:

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.

Some situations necessitate reading the request body. Since the request can be read only once, we need to cache the request body. You can use the CacheRequestBody filter to cache the request body before sending it downstream and getting the body from exchange attribute.

The following listing shows how to cache the request body GatewayFilter:

CacheRequestBody extracts the request body and converts it to a body class (such as java.lang.String, defined in the preceding example). CacheRequestBody then places it in the attributes available from ServerWebExchange.getAttributes(), with a key defined in ServerWebExchangeUtils.CACHED_REQUEST_BODY_ATTR.

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:

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.

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

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):

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

The JSONToGRPCFilter GatewayFilter Factory converts a JSON payload to a gRPC request.

The filter takes the following arguments:

This file can be generated using protoc and specifying the --descriptor_set_out flag:

application.yml.

When a request is made through the gateway to /json/hello, the request is transformed by using the definition provided in hello.proto, sent to com.example.grpcserver.hello.HelloService/hello, and the response back is transformed to JSON.

By default, it creates a NettyChannel by using the default TrustManagerFactory. However, you can customize this TrustManager by creating a bean of type GrpcSslConfigurer:

This filter allows caching the response body and headers to follow these rules:

This filter (which configures the local response cache per route) is available only if the local response global cache is enabled.

It accepts the first parameter to override the time to expire a cache entry (expressed in s for seconds, m for minutes, and h for hours) and a second parameter to set the maximum size of the cache to evict entries for this route (KB, MB, or GB).

The following listing shows how to add local response cache GatewayFilter:

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:

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

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

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

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

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

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

This prefixes /mypath to the path of all matching requests. So a request to /hello is sent to /mypath/hello.

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:

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:

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

The RemoveJsonAttributesResponseBody GatewayFilter factory takes a collection of attribute names to search for, an optional last parameter from the list can be a boolean to remove the attributes just at root level (that’s the default value if not present at the end of the parameter configuration, false) or recursively (true). It provides a convenient method to apply a transformation to JSON body content by deleting attributes from it.

The following example configures an RemoveJsonAttributesResponseBody GatewayFilter:

This removes attributes "id" and "color" from the JSON content body at root level.

The following example configures an RemoveJsonAttributesResponseBody GatewayFilter that uses the optional last parameter:

This removes attributes "id" and "color" from the JSON content body at any level.

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:

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

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:

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

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:

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.

The RequestHeaderSize GatewayFilter factory takes maxSize and errorHeaderName parameters. The maxSize parameter is the maximum data size allowed by the request header (including key and value). The errorHeaderName parameter sets the name of the response header containing an error message, by default it is "errorMessage". The following listing configures a RequestHeaderSize GatewayFilter:

This will send a status 431 if size of any request header is greater than 1000 Bytes.

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:

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

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.

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.

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:

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.

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:

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.

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:

If you integrate 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, per the recommendation made in this blog post.

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

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

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:

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:

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

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

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:

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

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:

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:

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:

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:

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

The Retry GatewayFilter factory supports the following parameters:

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

The following listing configures a Retry GatewayFilter:

A simplified "shortcut" notation can be added with a single status and method.

The following two examples are equivalent:

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:

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:

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

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

A Token Relay is where an OAuth2 consumer acts as a Client and forwards the incoming token to outgoing resource requests. The consumer can be a pure Client (like an SSO application) or a Resource Server.

Spring Cloud Gateway can forward OAuth2 access tokens downstream to the services it is proxying. To add this functionality to the gateway, you need to add the TokenRelayGatewayFilterFactory like this:

or this

and it will (in addition to logging the user in and grabbing a token) pass the authentication token downstream to the services (in this case /resource).

To enable this for Spring Cloud Gateway add the following dependencies

How does it work? The {githubmaster}/src/main/java/org/springframework/cloud/gateway/security/TokenRelayGatewayFilterFactory.java[filter] extracts an access token from the currently authenticated user, and puts it in a request header for the downstream requests.

For a full working sample see this project.

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:

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:

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 spring.cloud.gateway.metrics.enabled property is not set to false. This filter adds a timer metric named spring.cloud.gateway.requests with the following tags:

In addition, through the spring.cloud.gateway.metrics.tags.path.enabled property (by default, false), you can activate an extra metric with the path tag:

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

The LocalResponseCache runs if its associated property is enabled (spring.cloud.gateway.filter.local-response-cache.enabled) and activates a local cache for all responses that meet the following criteria: - The request is a bodiless GET. - The response has one of the following status codes: HTTP 200 (OK), HTTP 206 (Partial Content), or HTTP 301 (Moved Permanently). - The HTTP Cache-Control header allows caching (that means it does not have any of the following values: no-store present in the request and no-store or private present in the response).

It accepts two configuration parameters: - spring.cloud.gateway.filter.local-response-cache.size: Sets the maximum size of the cache to evict entries for this route (in KB, MB and GB). - spring.cloud.gateway.filter.local-response-cache.timeToLive Sets the time to expire a cache entry (expressed in s for seconds, m for minutes, and h for hours). If none of these parameters are configured but the global filter is enabled, by default, it configures 5 minutes of time to live for the cached response.

This filter also implements the automatic calculation of the max-age value in the HTTP `Cache-Control header. If max-age is present on the original response, the value is rewritten with the number of seconds set in the timeToLive configuration parameter. In subsequent calls, this value is recalculated with the number of seconds left until the response expires.

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.

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.)

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.)

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:

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.

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.

The following listing configures a websocket routing filter:

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.

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.

The RemoveHopByHop Headers Filter 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-hop-by-hop.headers property to the list of header names to remove.

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):

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

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:

To enable RouteDefinition metrics, add spring-boot-starter-actuator as a project dependency. Then, by default, the metrics will be available as long as the property spring.cloud.gateway.metrics.enabled is set to true. A gauge metric named spring.cloud.gateway.routes.count will be added, whose value is the number of RouteDefinitions. This metric will be available from /actuator/metrics/spring.cloud.gateway.routes.count.

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

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

A per-route response-timeout with a negative value will disable the global response-timeout value.

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

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.

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.

The “global” CORS configuration is a map of URL patterns to Spring Framework CorsConfiguration. The following example configures CORS:

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 evaluate to true because the HTTP method is options.

The “route” configuration allows applying CORS directly to a route as metadata with key cors. Like in the case of global configuration, the properties belong to Spring Framework CorsConfiguration.

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:

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

This will default to true in a future release.

This section details how to retrieve route filters, including:

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

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

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:

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:

The following table describes the structure of the response:

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}.

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

Spring Cloud Gateway offers two RouteDefinitionRepository implementations. The first one is the InMemoryRouteDefinitionRepository which only lives within the memory of one Gateway instance. This type of Repository is not suited to populate Routes across multiple Gateway instances.

In order to share Routes across a cluster of Spring Cloud Gateway instances, RedisRouteDefinitionRepository can be used. To enable this kind of repository, the following property has to set to true: spring.cloud.gateway.redis-route-definition-repository.enabled Likewise to the RedisRateLimiter Filter Factory it requires the use of the spring-boot-starter-data-redis-reactive Spring Boot starter.

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

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.

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

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

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

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