Push an Express server and Deplo builds it and starts it, on a server you own, with HTTPS in front.
Detection runs on every deploy and is never stored, so a change to the project is picked up by the next push.
Short answers to what comes up before moving a Express app onto your own server.
Read the PORT variable: Deplo sets it to the app's port, and you can change that port in the settings.
In the app's settings, per environment. They are available during the build too, and secret values are write only: nothing reads them back.
No. The new container has to pass its health check before the old one is retired.
Answer three questions and pick a host, or install Deplo on a server you already have. It's free, and leaving is as easy as arriving. What you do with the money you save is your business.