Create a Docker container which runs the CMD as a limited user but also allow that user access to become root using sudo. Useful for our internal container manager which only allows access to running containers service user.

Dockerfile

FROM ubuntu:xenial
RUN apt-get update && \
    apt-get -y --no-install-recommends upgrade && \
    rm -rf /var/lib/apt/lists/*

# Create a limited user, allow sudo access (requiring a password) and set an encrypted password for the user.
# Password hash created using:
# $ mkpasswd  -m sha-512 -S saltsalt -s <<< pa$$w0rd
RUN addgroup  limited-user && \
    adduser --system -gid 1000 limited-user && \
    usermod -p '$6$saltsalt$xzjaZOYawx.Y3cAmj0pmAXjaj7649kiuKFuYSdjRuvxatA1QcXiiybXrqGf4iLUKNnB5i0TPCgwo4kcjHUrO/0' limited-user && \
    echo "limited-user	ALL=(ALL:ALL) ALL" >> /etc/sudoers

USER limited-user

CMD ["bash"]