Dockerized executable read/write on host filesyste

Question

I just dockerized an executable that reads from a file and creates a new file in the very directory that file came from.

I want to use Docker in that setup, so that I avoid installing numerous third-party libraries in the production environment.

My problem now: I have file /this/is/a.file on my underlying (host) file system and my executable is supposed to create /this/is/b.file.

As far as I see it, the only chance to get this done is by mapping a volume that points to /this/is and then let the executable know where I mounted it to in the docker, container.

Am I right? Or is there a way that I just pass docker run mydockerizedstuff /this/is/a.file without using Docker volumes?

Answer 1

You're correct, you need to pass in /this/is as a volume and the executable will write to that location.

If you want to constrain the thing even more, you can pass /this/is/b.file as a volume. You need to create it (simply via touch) beforehand, otherwise Docker will consider it a directory and create it as such for you, but you'll know that the thing won't be able to create /this/is/c.file or any other thing.