Thanks a lot for the support 
You’re totally right, but the tricky part is also that I want to build the escript directly inside the container to make it totally dependent to it so that I can share just the built image.
Right now I’ve managed to accomplish something with the following Dockerfile but I’m sincerely not sure about the COPY . .
# Dockerfile
FROM elixir:1.7.3-alpine
# install build dependencies
RUN apk add --update git
# prepare build dir
RUN mkdir /app
WORKDIR /app
# install hex + rebar
RUN mix local.hex --force && \
mix local.rebar --force
# set build ENV
ENV MIX_ENV=prod
# install mix dependencies
# COPY mix.exs mix.lock ./
# COPY config ./
# COPY deps ./
# COPY lib ./
COPY . .
RUN mix deps.get && \
mix escript.build
ENTRYPOINT ["./myscript"]
