The Convox router listens on ports 80 and 443 and handles SSL termination for you. You will need to define the port on which your application is listening.
services: web: port: 3000
Your service should listen for HTTP requests on this port.
You can specify that your application is listening on HTTPS:
services: web: port: https:3001
This syntax implies that your container is listening on HTTPS for requests between the router and the container.