Describe solution for user ownership of files

bash command

docker-compose build --build-arg DEV_USER=`id -u` my_project

Dockerfile

FROM elixir:1.6.5-alpine

ARG DEV_USER=1000

RUN apk add --no-cache \
  # bash terminal Support
	bash \
	# development - could be separated/virtual for removal, but lets just get the bin going -BJG
	inotify-tools wget curl smem tar gcc g++ libc-dev libffi-dev make \
	# utilities
	bzip2 unzip xz git \
	# bring in elixir
	elixir erlang-crypto erlang-inets erlang-xmerl erlang-syntax-tools \
	erlang-parsetools erlang-runtime-tools erlang-tools erlang-dev \
	# postgres
	postgresql-client \
	# NodeJS for compiling assets
	nodejs

# Expose port 5000 to the Docker host, so we can access it
# from the outside.
EXPOSE 5000

# Setup the assets directory and install the packages
RUN mkdir -p /app/assets
WORKDIR /app/assets
COPY assets/package.json assets/package-lock.json ./

# Create a user and group that has the same uid as the user running the host container
RUN addgroup -g ${DEV_USER} -S dev_user && \
		adduser -u ${DEV_USER} -S dev_user -G dev_user

# Activate the new user
USER ${DEV_USER}

# hex and rebar
RUN mix local.hex --force && \
    mix local.rebar --force

# Install the Phoenix framework itself
RUN mix archive.install --force https://github.com/phoenixframework/archives/raw/master/phoenix_new.ez

WORKDIR /app

CMD ["mix", "do", "deps.get", "deps.compile", "compile", "ecto.migrate", "phx.server"]