Free ebook, have not read but it may interest some here.

HackerSploit Docker Security Essentials eBook Linode
https://www.linode.com/content/hackersploit-docker-security-essentials-ebook/

>What's Inside
>
>This guide focuses on securing the Docker platform on Linux. Follow along with the techniques demonstrated in this guide. All you need is a Linux server with Docker installed and running as well as a:
>
> fundamental knowledge of Docker and Docker CLI commands;
> functional knowledge of Linux terminal commands; and a
> fundamental knowledge of systemd and Linux init systems.