You can use :code.priv_dir(app) to get the priv directory directly as well, it’s what I typically use in my applications.

Thank you @michalmuskala. I’m going to try this and report back!

EDIT: Michal’s answer does work. Marking it as the solution.

New versions of your application will have a slightly different path (as the path includes the version of your app in a release), but the same version will always be the same path, regardless of OTP version, Elixir version, etc.

Yeah my general advice along these lines is to use priv for anything version-specific and/or static data/assets and to rely on something more well-known of your own creation in the filesystem for stateful data, i.e. /var/myapp/. You could also use the var directory created by the release, which you can obtain via the RELEASE_MUTABLE_DIR environment variable exposed to the release (which is used for temporary files like pipes, generated configs, and log files). That said, I would still tend towards using a directory like /var/myapp myself, since you can avoid clutter and manage it’s permissions and so on separately.