Add ejabberd development container

ejabberd-mix/Dockerfile

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+FROM alpine:3.4
+MAINTAINER ProcessOne <contact@process-one.net>
+
+# Install elixir from apk
+RUN apk --update add build-base zlib-dev openssl-dev yaml-dev expat-dev \
+   elixir erlang-crypto erlang-syntax-tools erlang-eunit erlang-mnesia && rm -rf /var/cache/apk/*
+
+# Install Hex+Rebar
+RUN mix local.hex --force && \
+    mix local.rebar --force
+
+EXPOSE 5222 5280
+
+ENTRYPOINT ["/usr/bin/mix"]
+
+CMD ["compile"]

ejabberd-mix/README.md

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+# ejabberd image for developers
+
+Thanks to this image, you can build ejabberd with dependencies provided in
+Docker image, without the need to install build software
+(despite Docker) directly on your own machine.
+
+Please note that this image can likely be reused as is to build other Erlang or
+Elixir software.
+
+## Building ejabberd from source 
+
+You can build ejabberd from source with all dependencies, with the following
+commands:
+
+```bash
+git clone https://github.com/processone/ejabberd.git
+docker run --rm -v $(pwd):$(pwd) -w $(pwd) ejabberd/mix do deps.get, deps.compile, compile
+```
+
+# Run ejabberd with mix command-line tool attached
+
+```bash
+docker run --rm -it -p 5222:5222 -p 5280:5280 -v $(pwd):$(pwd) -w $(pwd) --entrypoint="/usr/bin/iex" ejabberd/mix -S mix
+```
+
+You can then create a user from Elixir and connect with an XMPP client.
+
+# Get into the container
+
+If you want to run Erlang command line, you can do so by opening a shell inside
+the container:
+
+```bash
+docker run -it -v $(pwd):$(pwd) -w $(pwd) --entrypoint="/bin/sh" ejabberd/mix
+```
+
+# Build the image
+
+Building the image is not needed if you simply want to use it. You can simply
+use the one from [ejabberd Docker
+Hub](https://hub.docker.com/u/ejabberd/dashboard/).
+
+```bash
+docker build -t ejabberd/mix .
+```
+
+# Troubleshooting
+
+## Clock resync
+
+If you have warning about file timestamp being out of sync (Like 'Clock skew detected'),
+you may want to force resync your clock before running the build. Docker on
+MacOS does not force clock resync of Docker after the laptop went to sleep.
+
+You can force clock resync as follow:
+
+```bash
+docker run -it  --rm --privileged --entrypoint="/sbin/hwclock" ejabberd/mix -s
+```
+
+You can check if the clock of your laptop is in sync with the one inside Docker
+with the following command:
+
+```bash
+docker run --rm --entrypoint="/bin/sh" ejabberd/mix -c date -u && date -u
+```
+