How to make Zuul dynamic routing based on HTTP method and resolve target host by 'serviceId'?

Question

How to make Zuul dynamic routing based on HTTP method (GET/POST/PUT...)? For example, when you need to route the POST request to the different host instead of the default one described in 'zuul.routes.*'...

zuul:
  routes:
    first-service:
      path: /first/**
      serviceId: first-service
      stripPrefix: false

    second-service:
      path: /second/**
      serviceId: second-service
      stripPrefix: false

I.e. when we request 'GET /first' then Zuul route the request to the 'first-service', but if we request 'POST /first' then Zuul route the request to the 'second-service'.

Tania

Answer 1

To implement dynamic routing based on HTTP method we can create a custom 'route' type ZuulFilter and resolve 'serviceId' through DiscoveryClient. Fore example:

@Component
public class PostFilter extends ZuulFilter {

    private static final String REQUEST_PATH = "/first";
    private static final String TARGET_SERVICE = "second-service";
    private static final String HTTP_METHOD = "POST";

    private final DiscoveryClient discoveryClient;

    public PostOrdersFilter(DiscoveryClient discoveryClient) {
        this.discoveryClient = discoveryClient;
    }

    @Override
    public String filterType() {
        return "route";
    }

    @Override
    public int filterOrder() {
        return 0;
    }

    @Override
    public boolean shouldFilter() {
        RequestContext context = RequestContext.getCurrentContext();
        HttpServletRequest request = context.getRequest();
        String method = request.getMethod();
        String requestURI = request.getRequestURI();
        return HTTP_METHOD.equalsIgnoreCase(method) && requestURI.startsWith(REQUEST_PATH);
    }

    @Override
    public Object run() {

        RequestContext context = RequestContext.getCurrentContext();
        List<ServiceInstance> instances = discoveryClient.getInstances(TARGET_SERVICE);
        try {
            if (instances != null && instances.size() > 0) {
                context.setRouteHost(instances.get(0).getUri().toURL());
            } else {
                throw new IllegalStateException("Target service instance not found!");
            }
        } catch (Exception e) {
            throw new IllegalArgumentException("Couldn't get service URL!", e);
        }
        return null;
    }
}

Tania

@Cepro, how do I do it that it will cater not just POST request but all kinds of request? Thanks. – Liquate

For 'all kinds of requests' you should simply use the standard Zuul functionality that works for every HTTP methods based on their request path. – Tania

ok. By the way, is context.setRouteHost(...) needs the full URL or this just the host name e.g localhost or IP? – Liquate

It's a full URL. Try to take a look in doc... – Tania

@Cepr0, what about load balancing the second-service? Is it doable that way? – Roguery

@Roguery Maybe, if you implement for example Round-robin algorithm. Why not?.. – Tania

Answer 2

@Cepr0's solution is right. Here I am proposing just a simpler way (without service discovery). Assuming you have that route:

zuul:
    routes:
        first:
            path: /first/**
            # No need for service id or url

Then you can route requests for '/first' route in 'route' type filter just by setting location to request context.

@Component
    public class RoutingFilter extends ZuulFilter {

    @Override
    public String filterType() {
        return ROUTE_TYPE;
    }

    @Override
    public int filterOrder() {
        return 0;
    }

    @Override
    public boolean shouldFilter() {
        return true;
    }

    @Override
    public Object run() throws ZuulException {
        /* Routing logic goes here */
        URL location = getRightLocationForRequest();
        ctx.setRouteHost(location);

        return null;
    }
}

Parenthood