Super fast JS Docker images by caching NPM modules that haven't changed

Docerfile.cacheNPM

FROM library/node
MAINTAINER bobby@levelmoney.com

RUN mkdir /.npm
RUN mkdir /app

# cache (and skip if no changes) to the node_modules
WORKDIR /.npm
ADD package.json /.npm/package.json
# Set the version in the cache folder to 0.
# This is so that Docker will skip downloading node_modules when the version of the app increments but the node_modules do not.
RUN npm version 0.0.0
# npm takes a while and we should see progress. This should only happen with a library module changes
RUN npm install --production --loglevel verbose

# Copy over the app and build with Webpack
WORKDIR /app
ADD package.json /app/package.json
ADD src /app/src
ADD server /app/server
ADD webpack.config.js /app/webpack.config.js
# React/Webpack is based off of Megatome (https://github.com/Levelmoney/generator-megatome)
ADD webpack.dist.config.js /app/webpack.dist.config.js
RUN npm run build

COPY server /app/server

EXPOSE 8080
CMD PORT=8080 node --harmony server/server.js