Roll your own Elm Docker container

Dockerfile

# Build image with Node.js, Elm and Nginx
FROM debian:latest

# prepare
RUN apt-get -y update
RUN apt-get -y install apt-utils

# install curl, http://stackoverflow.com/questions/27273412/cannot-install-packages-inside-docker-ubuntu-image
RUN apt-get -y install curl

# node + npm, https://nodejs.org/en/download/package-manager/ (no sudo on debian)
RUN curl -sL https://deb.nodesource.com/setup_4.x | bash
RUN apt-get install -y nodejs # check with node: --version

# elm, https://www.npmjs.com/package/elm, https://github.com/rtfeldman/node-test-runner
RUN npm install -g elm
RUN npm install -g elm-test

# nginx, https://www.linode.com/docs/websites/nodejs/how-to-install-nodejs-and-nginx-on-debian
RUN apt-get install -y nginx

# make elm reactor and nginx accessible
EXPOSE 8000 80


# check installations with:
#   node --version
#   elm --version
#   elm-test --version
#   nginx -v

# run web servers:
#   elm reactor
#   service nginx start

this is helpful. thanks!

This doesn't make sense and I think violates the principles of Docker.
Why are you installing nginx? elm doesn't require node or npm either. So why are you install these?