Motivation

There are two main reasons for writing this article:

• need to set up dev environment in docker
• recent finding of coding tutorial Build your own docker

In addition I would like to understand docker in depth, because currently I know the concept, can use it as a black box, but nothing more. I am personally very curious about inner work of this tool.

Pre-existing knowledge

I would describe myself as a docker “advanced-beginner”

• understand the use case of this technology and facilitate it with the help of copy pasting from the internet
• have some awareness about its inner work: that it creates system inside my system, with its own memory scope, stripped out of everything beyond essentials
• wrote a Dockerfile and know how crucial (and useful) it is for automatization
• wrote a docker-compose and run it, also understand use-case of this tool
• wrote Jenkins pipeline using docker images
• created working dev environment in docker, consisting of ubuntu image and postgres database, deployed with docker-compose, to which I connect via SSH

Especially during this last point (dev-env), I felt inner need to better understand it, how Dockerfile file works, how it rebuilds, how docker-compose uses Dockerfile, is it rebuilt every time, how to write efficient tooling with it, and finally how it all works under the hood.

What have I learnt?

• standard output and errors handling, exit codes can be passed from child do parent
• chroot is just changing the root folder, so child process cannot name (access) other folders, called chroot jail
  • Create an empty temporary directory and chroot into it when executing the command. You’ll need to copy the binary being executed too. I do not know how to copy binary here
  • I am not exactly sure where the code is
  • https://tbhaxor.com/pivot-root-vs-chroot-for-containers/