Docker Copy and change owner

A --chown flag has finally been added to COPY:

COPY --chown=patrick hostPath containerPath

This new syntax seems to work on Docker 17.09.

See the PR for more information.

I think I found a solution, which works. Using a data volume container will do the trick. First I create the Data Volume Container, which contains the copy of my external directory:

FROM busybox
RUN mkdir /data
VOLUME /data
COPY /test /data/test
CMD /bin/sh

In my application container, where I have my users, which could look something like this

FROM ubuntu
RUN groupadd mygroup
RUN useradd -ms /bin/bash -G mygroup john
COPY setpermissions.sh /root/setpermissions.sh
CMD /root/setpermissions.sh && /bin/bash

The setpermissions script does the job of setting the user permissions:

#!/bin/bash

if [ ! -e /data/.bootstrapped ] ; then
  chown -R john:mygroup /data
  touch /data/.bootstrapped
fi

Now I just have to use the --volumes-from <myDataContainerId> when running the application container.