How to run PHP in a container :
1. Begin a docker file for an existing php cron app (when all you know is php, everything looks like a php app)
2. Set the FROM.. Apt get update .. Do composer install
3. Builds the image
4. Discover I need git
5. Add git to apt get install step
6. Builds the image
7. Launch the php script
8. Fatal : use of undefined constant SOL_UDP
9. Opens the source code of the third party. The there's no mention of where that constant is from.
10. Spend many minutes online to find what's missing.
11. Find the PHP sockets page about that option. Digs into the documentation to find out that's missing from the installed PHP.
12. Find out I need to add a step to install the socket extension in my docker file.
13. Build the image again
14. Execute it, finally it works
15. Remember why I hate php
(for brevity I've omitted the even more complex part of having to set up zlib)

How to install node js in a container image:
FROM node:8
ADD package.json
RUN npm install