Projects:Kubernetes

According to Wikipedia, Kubernetes (commonly stylized as k8s) is an open-source container orchestration system for automating application deployment, scaling, and management. I've heard a lot about it, and it seems to solve some problems I'm encountering sometimes, so I'd like to get to know it better. While doing so, I wanted to make a write-up of what I found out.

This page is not intended as a tutorial, but it will link to various tutorials I found useful. In this way, I hope that it can be used as a reference for someone setting up Kubernetes to be able to learn about it more quickly.

Disclaimer: I'm a beginner in the Kubernetes area, so this tutorial will contain errors. Please correct errors where you find them, and if possible, write some explanation! The "I" in this article is Sjors, but parts are possibly written by other people.

= Problem

We start with a Linux desktop, running some version of Arch Linux. Someone wants to run an application on it for which only binaries are available, but those binaries were compiled on Ubuntu. Now, system libraries are different between Arch Linux and Ubuntu, and while it's possible to create binaries that run independent of system libraries (called "static binaries"), in this particular situation let's assume the binaries aren't static, but you still want to run them on your Arch installation.

You can get a second machine and run Ubuntu on it, or similarly you could use a Virtual Machine. But, there's a simpler and more efficient solution: Docker allows you to install, within your Linux distribution (the "host"), another Linux distribution (let's call it "guest" for now). The host and the guest may be completely different – technically, only the kernel of the host is used, and of course the host and guest must have compatible processor architectures. You run the guest environment within Docker (a "Docker Container") and run that binary in it.

This is how easy that is:

``` sjors@somebox:~$ lsb_release -a LSB Version: 1.4 Distributor ID: Arch Description: Arch Linux Release: rolling Codename: n/a sjors@somebox:~$ docker run -ti ubuntu:bionic bash root@a5b210d251c2:/# apt-get update && apt-get -y install lsb-release [....] root@a5b210d251c2:/# lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 18.04.1 LTS Release: 18.04 Codename: bionic ```

Now, Docker has some problems of its own.

= Concepts

In this section, I'll explain some of Kubernetes' concepts quickly, and add links if you want to know more.