Updated Dockerfile

This does two things:

1. No longer user onbuild. Onbuild is deprecated for [reasons outlined
   here][reasons].

2. Build static assets with the container. Before, the static assets
   wouldn't be built causing the container to crash on start up.

[reasons]: https://github.com/docker-library/official-images/issues/2076

.dockerignore

@@ -0,0 +1,4 @@
+# Ignore files not needed for building and running to keep image size low.
+.git/
+node_modules/
+

Dockerfile

@@ -1,5 +1,28 @@
-FROM node:7.8.0-onbuild
+FROM node:7.8.0
+
+# Install runtime dependencies and remove state generated by apt-get before
+# creating intermediate image.
 RUN apt-get update && apt-get install -y mediainfo && rm -rf /var/lib/apt/lists/*
-COPY config.docker.js config.js
+
+# Create app working directory.
+RUN mkdir -p /usr/src/app
+WORKDIR /usr/src/app
+COPY . /usr/src/app
+
+# Copy docker configuration file. This allows for specifying common configs with
+# just environment variables.
+COPY config.docker.js /usr/src/app/config.js
+
+# Install Dependencies and remove cache to keep image small. This is done in one
+# step to keep the cache out of intermediate image.
+RUN npm install && npm cache clean --force
+
+# Build static assets.
+RUN npm run build
+
+# Hints for consumers of the container.
 EXPOSE 3000
 VOLUME ["/data"]
+
+# Start application.
+CMD [ "npm", "start" ]