add react-express-mysql application sample

Signed-off-by: Anca Iordache <anca.iordache@docker.com>

samples/react-express-mysql/backend/Dockerfile

@@ -0,0 +1,36 @@
+# if you're doing anything beyond your local machine, please pin this to a specific version at https://hub.docker.com/_/node/
+FROM node:10
+
+RUN mkdir -p /opt/app
+
+# set our node environment, either development or production
+# defaults to production, compose overrides this to development on build and run
+ARG NODE_ENV=production
+ENV NODE_ENV $NODE_ENV
+
+# default to port 80 for node, and 9229 and 9230 (tests) for debug
+ARG PORT=80
+ENV PORT $PORT
+EXPOSE $PORT 9229 9230
+
+# you'll likely want the latest npm, reguardless of node version, for speed and fixes
+RUN npm i npm@latest -g
+
+# install dependencies first, in a different location for easier app bind mounting for local development
+WORKDIR /opt
+COPY package.json package-lock.json* ./
+RUN npm install && npm cache clean --force
+ENV PATH /opt/node_modules/.bin:$PATH
+
+# check every 30s to ensure this service returns HTTP 200
+HEALTHCHECK --interval=30s CMD node healthcheck.js
+
+# copy in our source code last, as it changes the most
+WORKDIR /opt/app
+COPY . /opt/app
+
+# if you want to use npm start instead, then use `docker run --init in production`
+# so that signals are passed properly. Note the code in index.js is needed to catch Docker signals
+# using node here is still more graceful stopping then npm with --init afaik
+# I still can't come up with a good production way to run with npm and graceful shutdown
+CMD [ "node", "index.js" ]