Docker enables you to package up your application along with all of the application’s dependencies into a nice self-contained image. You can then use use that image to run your application in containers. The problem is you usually package up a lot more than what you need so you end up with a huge image and therefore huge containers. Most people who start using Docker will use Docker’s official repositories for their language of choice, but unfortunately if you use them, you’ll end up with images the size of the empire state building when you could be building images the size of a bird house. You simply don’t need all of the cruft that comes along with those images. If you build a Node image for your application using the official Node image, it will be a minimum of 643 MB because that’s the size of the official Node image.
I created a simple Hello World Node app and built it on top of the official Node image and it weighs in at 644MB.
That’s huge! My app is less than 1 MB with dependencies and the Node.js runtime is ~20MB, what’s taking up the other ~620 MB?? We must be able to do better.
What is a Microcontainer?
A Microcontainer contains only the OS libraries and language dependencies required to run an application and the application itself. Nothing more.
Rather than starting with everything but the kitchen sink, start with the bare minimum and add dependencies on an as needed basis.
Taking the exact same Node app above, using a really small base image and installing just the essentials, namely Node.js and its dependencies, it comes out to 29MB. A full 22 times smaller!
Try running both of those yourself right now if you’d like, docker run –rm -p 8080:8080 treeder/tiny-node:fat, then docker run –rm -p 8080:8080 treeder/tiny-node:latest. Exact same app, vastly different sizes.