Caching npm install with Docker

Dockerfile

FROM nodesource/node:trusty
EXPOSE 8080
WORKDIR /src

# Install dependencies
# See http://www.clock.co.uk/blog/a-guide-on-how-to-cache-npm-install-with-docker
ADD package.json /src/package.json
RUN npm install

ADD . /src
# Run npm install again in case a package.json change was not picked up by
# Docker.
RUN npm install
CMD [ "npm", "start" ]