How to dynamically route an incoming request by using a URL->responsible-backend-service mapping service? - spring-cloud

Question

I am new to spring-cloud-gateway and I can't answer the question if I solved my problem the intended way. I hope someone can point me into the right direction, give advice or provide some exemplary sample code.
Requirement:
An incoming request at my spring-cloud-gateway service shall be forwarded to the correct backend service (there are X of such backend services, each responsible for a specific task).
The request itself does not contain enough information to decide which backend service to route to.
An additional REST-service exists that maps an arbitrary URL-to-responsible-backend-service-name. The response format is some small JSON, containing the name of the backend-service to forward to.
What would be the easiest/best/smartest/intended solution to implement this functionality with spring-cloud-gateway?
I tried implementing a GatewayFilter that first calls the mapping-service and depending on the result set GATEWAY_REQUEST_URL_ATTRfor the exchange.
This works ok. But I have additional questions.
Is it possible to omit the .uri("not://needed")) part in the route setup?
Why does the order value need to be higher than 9999? (see code example)
#SpringBootApplication
#RestController
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
#Bean
public RouteLocator myRoutes(RouteLocatorBuilder builder) {
return builder.routes().route(r -> r
.alwaysTrue()
.filters(f -> f.filter(new CustomRequestFilter()))
.uri("not://needed")) // how to omit ?
.build();
}
public static class CustomRequestFilter implements GatewayFilter, Ordered {
#Override
public int getOrder() {
return 10000; // why order > 9999 ? (below 10000 does not work)
}
#Override
public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
return getBackendServiceMappingResult(exchange.getRequest().getURI().toString()) //async call to REST service mapping URL->backend service name
.flatMap(mappingResult -> {
URI uri = mapServiceNameToBackendService(mappingResult.getServiceName());
exchange.getAttributes().put(ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR, uri);
return chain.filter(exchange);
});
}
private URI mapServiceNameToBackendService(String serviceName) {
try {
switch (serviceName) {
case "serviceA": return new URI("http://httpbin.org:80/get");
case "serviceB": return new URI("https://someotherhost:443/");
}
} catch (URISyntaxException e) {
//ignore
}
return null;
}
}
static class MappingResult {
String serviceName;
public String getServiceName() {
return serviceName;
}
}
static Mono<MappingResult> getBackendServiceMappingResult(String uri) {
WebClient client = WebClient.create("http://localhost:8080");
return client.get().uri(uriBuilder -> uriBuilder.path("/mapping").queryParam("uri", uri).build()).retrieve().bodyToMono(MappingResult.class);
}
}
Is there a better approach (with spring-cloud-gateway) to solve the requirement?

Answer 1

You can use this
#Bean
public RouteLocator myRoutes(RouteLocatorBuilder builder) {
return builder.routes().route(r ->
r.alwaysTrue()
.filters(f-> {
f.changeRequestUri(serverWebExchange -> buildRequestUri(serverWebExchange, CustomRequestFilter));
return f;
})
.uri(env.getProperty("birdeye.platform.url")))
.build();
private Optional buildRequestUri(ServerWebExchange exchange,CustomRequestFilter customRequestFilter ){
boolean updateuri = true;
if(updateuri) {
ServerHttpRequest request = exchange.getRequest();
String path = request.getPath().pathWithinApplication().value();
try {
uriBiulder = UriComponentsBuilder.fromUri(new URI(backendUri)).path(backendPath)
} catch (URISyntaxException e) {
e.printStackTrace();
}
}else {
uriBiulder = new URI("https://paytm.com:8080/category/create")
}
return Optional.of(uriBiulder);
}