It’s possible that containers and container management tools like Docker will be the single most important thing to happen to the data center since the mainstream adoption of hardware virtualization in the 90s. In the past 12 months, the technology has matured beyond powering large-scale startups like Twitter and Yelp and found its way into the data centers of major banks, retailers and even NASA. When I first heard about Docker a couple years ago, I started off as a skeptic. I blew it off as skillful marketing hype around an old concept of Linux containers. But after incorporating it successfully into several projects at Spantree I am now a convert. It’s saved my team an enormous amount of time, money and headaches and has become the underpinning of our technical stack.
If you’re anything like me, you’re often time crunched and may not have a chance to check out every shiny new toy that blows up on Github overnight. So this article is an attempt to quickly impart 10 nuggets of wisdom that will help you understand what Docker is and why it’s useful.
Docker is a container management tool.
Docker is an engine designed to help you build, ship and execute applications stacks and services as lightweight, portable and isolated containers. The Docker engine sits directly on top of the host operating system. Its containers share the kernel and hardware of the host machine with roughly the same overhead as processes launched directly on the host machine.
But Docker itself isn’t a container system, it merely piggybacks off the existing container facilities baked into the OS, such as LXC on Linux. These container facilities have been baked into operating systems for many years, but Docker provides a much friendlier image management and deployment system for working with these features.
Docker is not a hardware virtualization engine.
When Docker was first released, many people compared it to virtual machine hypervisors like VMWare, KVM and Virtualbox. While Docker solves a lot of the same problems and shares many of the same advantages as hypervisors, Docker takes a very different approach. Virtual machines emulate hardware. In other words, when you launch a VM and run a program that hits disk, its generally talking to a "virtual" disk. When you run a CPU-intensive task, those CPU commands need to be translated to something the host CPU understands. All these abstractions come at a cost: two disk layers, two network layers, two processor schedulers, even two whole operating systems that need to be loaded into memory. These limitations typically mean you can only run a few virtual machines on a given piece of hardware before you start to see an unpleasant amount of overhead and churn. On the other hand, you can theoretically run hundreds of Docker containers on the same host machine without issue.
All that being said, containers aren’t a wholesale replacement for virtual machines. Virtual machines provide a tremendous amount of flexibility in areas where containers generally can’t. For example, if you want to run a Linux guest operating system on top of a Windows host, that’s where virtual machines shine.
Download the whitepaper to read the rest of the list of 10 Things You Need to Know About Docker
Whitepaper by Cedric Hurst, Principal at Spantree