This key expects the port number to be exposed for this application. Every container port will be mapped outside to 80/443. Think of:
docker run -it -p 80:4000 -p 443:4000 ...
Please note: With our shared hosting plans you can only expose HTTP, and not TCP ports like 22 or 3306. For now, you can only expose one port per app.
If you are running several apps within one project, you do not need to expose ports between apps (e.g. exposing the mysql port to the apache container).
The following example exposes port 4000. From outside the service will be reachable at port 80 and 443: