Spring Forward Enters the Filter Again

6. Global Filters

The GlobalFilter interface has the same signature as GatewayFilter. These are special filters that are conditionally practical to all routes. (This interface and usage are subject area to alter in future milestones).

six.one Combined Global Filter and GatewayFilter Ordering

When a request comes in (and matches a Route) the Filtering Spider web Handler will add together all instances of GlobalFilter and all route specific instances of GatewayFilter to a filter concatenation. This combined filter chain is sorted past the org.springframework.core.Ordered interface, which tin be ready by implementing the getOrder() method or past using the @Order annotation.

As Spring Cloud Gateway distinguishes between "pre" and "post" phases for filter logic execution (encounter: How Information technology Works), the filter with the highest precedence will be the first in the "pre"-phase and the last in the "mail service"-phase.

ExampleConfiguration.coffee.

                          @Edible bean                                      @Order(-ane)                        public            GlobalFilter a() {            render            (exchange, chain) -> {         log.info("start pre filter");            return            chain.filter(exchange).and so(Mono.fromRunnable(() -> {             log.info("tertiary mail service filter");         }));     }; }                          @Bean                                      @Order(0)                        public            GlobalFilter b() {            return            (commutation, chain) -> {         log.info("second pre filter");            return            chain.filter(commutation).then(Mono.fromRunnable(() -> {             log.info("second mail filter");         }));     }; }                          @Bean                                      @Order(1)                        public            GlobalFilter c() {            return            (exchange, chain) -> {         log.info("third pre filter");            return            concatenation.filter(exchange).so(Mono.fromRunnable(() -> {             log.info("first post filter");         }));     }; }

half-dozen.2 Forward Routing Filter

The ForwardRoutingFilter looks for a URI in the exchange attribute ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR. If the url has a forrard scheme (ie forrard:///localendpoint), it will use the Spring DispatcherHandler to handler the request. The path function of the asking URL volition exist overridden with the path in the forrard URL. The unmodified original url is appended to the listing in the ServerWebExchangeUtils.GATEWAY_ORIGINAL_REQUEST_URL_ATTR attribute.

6.iii LoadBalancerClient Filter

The LoadBalancerClientFilter looks for a URI in the exchange attribute ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR. If the url has a lb scheme (ie lb://myservice), information technology will utilise the Bound Cloud LoadBalancerClient to resolve the name (myservice in the previous example) to an bodily host and port and replace the URI in the aforementioned attribute. The unmodified original url is appended to the list in the ServerWebExchangeUtils.GATEWAY_ORIGINAL_REQUEST_URL_ATTR attribute. The filter will as well wait in the ServerWebExchangeUtils.GATEWAY_SCHEME_PREFIX_ATTR attribute to encounter if it equals lb then the aforementioned rules apply.

application.yml.

            spring:                          deject:                          gateway:                          routes:                          - id: myRoute                          uri: lb://service                          predicates:                          - Path=/service/**

	Note
	By default when a service instance cannot be found in the LoadBalancer a 503 volition be returned. You can configure the Gateway to render a 404 by setting spring.cloud.gateway.loadbalancer.use404=true.

Notation

The isSecure value of the ServiceInstance returned from the LoadBalancer volition override the scheme specified in the asking made to the Gateway. For example, if the request comes into the Gateway over HTTPS but the ServiceInstance indicates it is non secure, and so the downstream request will be made over HTTP. The contrary situation tin can also utilise. All the same if GATEWAY_SCHEME_PREFIX_ATTR is specified for the road in the Gateway configuration, the prefix will be stripped and the resulting scheme from the route URL will override the ServiceInstance configuration.

six.4 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 brand the downstream proxy request. The response is put in the ServerWebExchangeUtils.CLIENT_RESPONSE_ATTR exchange attribute for use in a later filter. (There is an experimental WebClientHttpRoutingFilter that performs the same function, but does not require netty)

6.five Netty Write Response Filter

The NettyWriteResponseFilter runs if there is a Netty HttpClientResponse in the ServerWebExchangeUtils.CLIENT_RESPONSE_ATTR substitution aspect. It is run after all other filters have completed and writes the proxy response back to the gateway client response. (There is an experimental WebClientWriteResponseFilter that performs the aforementioned office, just does not require netty)

half-dozen.6 RouteToRequestUrl Filter

The RouteToRequestUrlFilter runs if there is a Road object in the ServerWebExchangeUtils.GATEWAY_ROUTE_ATTR exchange attribute. Information technology creates a new URI, based off of the request URI, only updated with the URI attribute of the Road object. The new URI is placed in the ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR exchange aspect`.

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.

half-dozen.7 Websocket Routing Filter

The Websocket Routing Filter runs if the url located in the ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR exchange aspect has a ws or wss scheme. It uses the Spring Web Socket infrastructure to forwards the Websocket asking downstream.

Websockets may be load-counterbalanced by prefixing the URI with lb, such equally lb:ws://serviceid.

	Notation
	If you are using SockJS as a fallback over normal http, you should configure a normal HTTP route as well as the Websocket Route.

application.yml.

            spring:                          cloud:                          gateway:                          routes:                                 - id: websocket_sockjs_route                          uri: http://localhost:3001                          predicates:                          - Path=/websocket/info/**                                 - id: websocket_route                          uri: ws://localhost:3001                          predicates:                          - Path=/websocket/**

half-dozen.eight Gateway Metrics Filter

To enable Gateway Metrics add together leap-kick-starter-actuator as a project dependency. Then, by default, the Gateway Metrics Filter runs as long as the belongings jump.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 that the API will be routed to
• outcome: Outcome equally classified past HttpStatus.Series
• status: Http Status of the asking returned to the customer

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

	Notation
	To enable the pometheus endpoint add micrometer-registry-prometheus as a projection dependency.

6.ix Marking An Exchange As Routed

Later the Gateway has routed a ServerWebExchange it will mark that exchange every bit "routed" by adding gatewayAlreadyRouted to the substitution attributes. Once a asking has been marked as routed, other routing filters will non road the request again, essentially skipping the filter. There are convenience methods that yous can use to mark an substitution 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 information technology as "routed"

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Source: https://cloud.spring.io/spring-cloud-gateway/multi/multi__global_filters.html

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