Build a Docker image without a GitHub account?

I experimented this weekend with cloning Gladys to tinker with elements that are not intended to enrich the project. For example, I wanted to add the « Last 4h » option in the graphs, even though I know (and accept) that Pierre-Gilles does not want to add it to the official Gladys release.

And I do this also because I’m curious to explore Gladys’s code, and to take on the small technical challenge (at least for me it is one) of customizing Gladys by coding…

I managed to clone from GitHub, to modify the right files, to run the server and front-end parts (outside of Docker, just with the ‹ npm start ›), and it works. Now I’d like to do a build to install this customized version on my real instance, in Docker. But the information I found for this seems to involve adding my changes to a project on GitHub. And I’m not sure of the point of doing it that way, since I won’t need to share this version for others to test…

So my question is: How do I make a ‹ local › build? Then how do I deploy the result of that build to my production Docker?

But if that’s not possible or not simple, I’ll look at how to do it by going through a GitHub project…