Update Dockerfile

docker/Dockerfile

@@ -1,17 +1,28 @@
 FROM ubuntu:latest
+
 MAINTAINER Sah Lee <contact@leesah.name>
 
-ENV PORT 8388
-EXPOSE $PORT
-
-ENV CONF /etc/shadowsocks.json
-VOLUME ["/etc/shadowsocks.json"]
-
-CMD ssserver -p $PORT -c $CONF
-
+# Set up building environment
 RUN apt-get update
 RUN apt-get install -y git-core python python-setuptools
+
+# Get the latest code, build and install
 RUN git clone https://github.com/shadowsocks/shadowsocks.git
 RUN cd shadowsocks
 RUN python setup.py build
 RUN python setup.py install
+
+# Tear down building environment and delete git repository
+RUN apt-get --purge autoremove -y git-core python python-setuptools
+RUN cd ..
+RUN rm -rf shadowsocks
+
+# Config file can be in a separated container
+ENV CONF /etc/shadowsocks.json
+VOLUME ["$CONF"]
+
+# Port in the config file won't take affect. Instead we'll use 8388.
+ENV PORT 8388
+EXPOSE $PORT
+
+CMD ssserver -c $CONF -p $PORT