Gosu usage in Docker

docker-entrypoint.sh

#!/bin/bash
set -e

# Change uid and gid of node user so it matches ownership of current dir
if [ "$MAP_NODE_UID" != "no" ]; then
    if [ ! -d "$MAP_NODE_UID" ]; then
        MAP_NODE_UID=$PWD
    fi

    uid=$(stat -c '%u' "$MAP_NODE_UID")
    gid=$(stat -c '%g' "$MAP_NODE_UID")

    echo "dev ---> UID = $uid / GID = $gid"

    export USER=dev

    usermod -u $uid dev 2> /dev/null && {
      groupmod -g $gid dev 2> /dev/null || usermod -a -G $gid dev
    }
fi

echo "**** GOSU dev $@ ..."

exec /usr/local/bin/gosu dev "$@"

Dockerfile

FROM ubuntu

RUN apt-get install ...

# grab gosu for easy step-down from root
ENV GOSU_VERSION 1.10
RUN set -x \
  && curl -sSLo /usr/local/bin/gosu "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$(dpkg --print-architecture)" \
  && curl -sSLo /usr/local/bin/gosu.asc "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$(dpkg --print-architecture).asc" \
  && export GNUPGHOME="$(mktemp -d)" \
  && gpg --keyserver ha.pool.sks-keyservers.net --recv-keys B42F6819007F00F88E364FD4036A9C25BF357DD4 \
  && gpg --batch --verify /usr/local/bin/gosu.asc /usr/local/bin/gosu \
  && rm -r "$GNUPGHOME" /usr/local/bin/gosu.asc \
  && chmod +x /usr/local/bin/gosu \
  && gosu nobody true

# Add local user 'dev'
RUN groupadd -r dev --gid=9001 && useradd -r -g dev --uid=9001 dev
# Grant him sudo privileges
RUN echo "dev ALL=(root) NOPASSWD:ALL" > /etc/sudoers.d/dev && \
    chmod 0440 /etc/sudoers.d/dev
    
# Do stuff with this user if needed
USER dev
ENV HOME /home/dev
WORKDIR $HOME
RUN ...

# Repass root 
USER root

# Copy entrypoint
COPY docker-entrypoint.sh /usr/local/bin/docker-entrypoint.sh
ENTRYPOINT ["/usr/local/bin/docker-entrypoint.sh"]

CMD ["bash"]

entrypoint.sh

#!/bin/bash

# Add local user
# Either use the LOCAL_USER_ID if passed in at runtime or
# fallback

USER_ID=${LOCAL_USER_ID:-9001}

echo "Starting with UID : $USER_ID"
useradd --shell /bin/bash -u $USER_ID -o -c "" -m user
export HOME=/home/user

exec /usr/local/bin/gosu user "$@"

su-exec_alpine

FROM alpine

RUN apk add --update --no-cache su-exec && \
    rm -rf /var/cache/apk/*

# Add entrypoint to dynamically change user uid when a container is started
COPY entrypoint.sh /usr/local/bin/entrypoint.sh

ENTRYPOINT ["/usr/local/bin/entrypoint.sh"]