Our current project requirement is to to route some requests to third-party external api servers. For this we are using spring zuul based router service.

zuul:
  routes
    test:
      path: /test/**
      serviceId: test
      url: http://my.api.server.com
    test2:
      path: /test2/**
      serviceId: test2
      url: http://my.api.server.com // but through an external proxy

Now the requirement is that for some endpoints, the requests to the external api server has be routed through some external proxy server, not owned by us,

How to do this via a curl is:

curl <external_api_server>/api/v1/user -k \
  -x tntqyhnhjym.sandbox.verygoodproxy.com:8080 \
  -H "Content-type: application/json" \
  -d '{"card_number": "tok_sandbox_t8VSoovCuHA779eJGZhKvg", ... }'

-x <proxy> redirects the request through the given proxy. How to do this via spring-zuul server?

There is one lead, I have gotten? https://github.com/spring-cloud/spring-cloud-netflix/issues/2320. Not clean, in the sense that I would need to extendSimpleHostRoutingFilter of zuul

Option 1 - Reverse Proxy Server ( that uses the proxy)

You could setup a reverse proxy - that is configured to go through the proxy. Your reverse proxy would be started with the parameters (either in e.g. java or nodejs) to use the external proxy. This reverse proxy would be a different process that would pass all requests through the proxy you want.

You could do it either through setting up a second zuul proxy application or through a nodejs reverse proxy (express or node-http-proxy).

Second zuul application (only for externals)

So if you used zuul, you would make a second application with the following:

   test2:
      path: /proxied-test2/**
      serviceId: test2
      url: http://my.api.server.com 

You would then start this server on the same server with the parameters of your proxy and on a specific port (something like e.g. 9200) so e.g.

-Dhttp.proxyHost=localhost -Dhttp.proxyPort=8888

Original Application

In your original application, you would replace your route to now be the following.

zuul:
  routes
    test:
      path: /test/**
      serviceId: test
      url: http://my.api.server.com
    test2:
      path: /test2/**
      serviceId: test2
      url: http://localhost:9200/proxied-test2/

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Option 2: Use a scriptable http proxy server

You could setup a proxy server and then setup some exceptions and rules about which requests should be routed through the proxy and which requests should work without the proxy.

The second step is to configure your application to use the local proxy server specified in step 1. For this you can use the the following command-line parameters:

-Dhttp.proxyHost=localhost -Dhttp.proxyPort=8888

I have configured exclude lists for proxy servers in the past, but I never configured/scripted include lists. In your case, it would make more sense to have include lists so I would test scriptable/programmable proxy servers, e.g.:

• https://mitmproxy.org/ - scriptable via mitmdump

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