I think most of the ideas are presented here: https://github.com/martensson/nixy

In essence there is a wrapper that:

- reads service information and current backend instances out of service catalog (either Marathon or Consul)

- writes nginx configuration

- runs nginx configtest

- tells nginx to reload its configuration

Nixy referenced above takes service information directly from Marathon event stream but I usually have Consul so I use homebaked consul-template + nginx solution.