Docker container file permissions

Question

I have a java application that saves a CSV file to the root folder of the application. I am trying to create a docker image of this and run it as a container. However, I want a non-root user with ID of 1010 to be able to access this file and not root. I get errors when trying to specify USER 1010 in my dockerfile

FROM adoptjdk (placeholder)
COPY ./myapp.jar /app/
USER 1010
WORKDIR /opt
EXPOSE PORTNO

That's just the basics of the dockerfile, essentially I want user 1010 to be able to access the CSV file that my java application creates. I am not sure where it saves my CSV file when it is run through docker.

Answer 1

If your application shall write to / inside the container, and your application shall be running as user id 1010, then just set the filesystem privileges accordingly. I chime in that it may not be the recommended setup, but it is not impossible.

So put in your Dockerfile lines like

RUN chmod 777 /

or to be a bit smoother check the GID of / with

RUN ls -ln /
RUN chmod 775 /

then ensure your java application runs with uid 1010 and the GID you saw from the filesystem. In short, such things are the same, be it inside the container or outside.