docker: move the docker image creation inside the main repository

This is a super simple start.
At minimum, configuration via environment variables (see #3543) needs to be
integrated in Etherpad to make this user-friendly.

Resolves #3524.

docker/Dockerfile

@@ -0,0 +1,52 @@
+# Etherpad Lite Dockerfile
+#
+# https://github.com/ether/etherpad-docker
+#
+# Author: muxator
+#
+# Version 0.1
+
+FROM node:latest
+LABEL maintainer="Etherpad team, https://github.com/ether/etherpad-lite"
+
+# install supervisor
+RUN apt-get update && apt-get install -y \
+	supervisor \
+	&& rm -rf /var/lib/apt/lists/*
+
+# install supervisor.conf in a low layer of the container
+ADD supervisor.conf /etc/supervisor/supervisor.conf
+
+# git hash of the version to be built.
+# If not given, build the latest development version.
+ARG ETHERPAD_VERSION=develop
+
+# grab the ETHERPAD_VERSION tarball from github (no need to clone the whole
+# repository)
+RUN echo "Getting version: ${ETHERPAD_VERSION}" && \
+	curl \
+		--location \
+		--fail \
+		--silent \
+		--show-error \
+		--output /opt/etherpad-lite.tar.gz \
+		https://github.com/ether/etherpad-lite/archive/"${ETHERPAD_VERSION}".tar.gz && \
+	mkdir /opt/etherpad-lite && \
+	tar xf /opt/etherpad-lite.tar.gz \
+		--directory /opt/etherpad-lite \
+		--strip-components=1 && \
+	rm /opt/etherpad-lite.tar.gz
+
+# install node dependencies for Etherpad
+RUN /opt/etherpad-lite/bin/installDeps.sh
+
+# Copy the custom configuration file, if present. The configuration file has to
+# be manually put inside the same directory containing the Dockerfile (we cannot
+# directly point to "../settings.json" for Docker's security restrictions).
+#
+# For the conditional COPY trick, see:
+#   https://stackoverflow.com/questions/31528384/conditional-copy-add-in-dockerfile#46801962
+COPY nop setting[s].json /opt/etherpad-lite/
+
+EXPOSE 9001
+CMD ["supervisord", "-c", "/etc/supervisor/supervisor.conf", "-n"]

docker/README.md

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+# Docker image
+
+This directory contains the files that are used to build the official Docker image on https://hub.docker.com/r/etherpad/etherpad.
+
+# Rebuilding with custom settings
+In order to use a personalized settings file, **you will have to rebuild your image**.
+
+All of these instructions are as a member of the `docker` group.
+
+Prepare your custom `settings.json` file:
+```bash
+cd <BASEDIR>/docker
+cp ../settings.json.template settings.json
+[ further edit your settings.json as needed]
+```
+
+Build the version you prefer:
+```bash
+# builds latest development version
+docker build --tag <YOUR_USERNAME>/etherpad .
+
+# builds latest stable version
+docker build --build-arg ETHERPAD_VERSION=master --tag <YOUR_USERNAME>/etherpad .
+
+# builds a specific version
+docker build --build-arg ETHERPAD_VERSION=1.7.5 --tag <YOUR_USERNAME>/etherpad .
+
+# builds a specific git hash
+docker build --build-arg ETHERPAD_VERSION=4c45ac3cb1ae --tag <YOUR_USERNAME>/etherpad .
+```
+
+# Downloading from Docker Hub
+If you are ok downloading a [prebuilt image from Docker Hub](https://hub.docker.com/r/etherpad/etherpad), these are the commands:
+```bash
+# gets the latest published version
+docker pull etherpad/etherpad
+
+# gets a specific version
+docker pull etherpad/etherpad:1.7.5
+```
+
+# Running your instance:
+
+To run your instance:
+```bash
+docker run --detach --publish <DESIDERED_PORT>:9001 <YOUR_USERNAME>/etherpad
+```
+
+And point your browser to `http://<YOUR_IP>:<DESIDERED_PORT>`

docker/nop

@@ -0,0 +1,4 @@
+THIS IS A DUMMY FILE
+
+It is used to trick Docker in doing a conditional COPY
+see: https://stackoverflow.com/questions/31528384/conditional-copy-add-in-dockerfile#46801962

docker/supervisor.conf

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+[supervisord]
+nodaemon=true
+
+[unix_http_server]
+file=/var/run//supervisor.sock
+chmod=0700
+
+[rpcinterface:supervisor]
+supervisor.rpcinterface_factory = supervisor.rpcinterface:make_main_rpcinterface
+
+[supervisorctl]
+serverurl=unix:///var/run//supervisor.sock
+
+[program:etherpad]
+directory=/opt/etherpad-lite
+command=node node_modules/ep_etherpad-lite/node/server.js
+user=root
+autostart=true
+autorestart=true
+