in ring id specify the port like this

(defn -main []
  (run-jetty app {:port (or (env/env :port)
                            9303)}))

@plins c-api emits justs a ring handler, which is, in your case the app. For production, I would recommend taking a look either at Luminus template (with +swagger) http://www.luminusweb.net/ or an example app https://github.com/yogthos/memory-hole/tree/master/src/clj/memory_hole. Both contain a main function where you can set the port easily. Hope this helps.