Why are Docker container images so large?

Question

I made a simple image through Dockerfile from Fedora (initially 320 MB).

Added Nano (this tiny editor of 1MB size), and the size of the image has risen to 530 MB. I\

Answer 1

Docker images are not large, you are just building large images.

The scratch image is 0B and you can use that to package up your code if you can compile your code into a static binary. For example, you can compile your Go program and package it on top of scratch to make a fully usable image that is less than 5MB.

The key is to not use the official Docker images, they are too big. Scratch isn't all that practical either so I'd recommend using Alpine Linux as your base image. It is ~5MB, then only add what is required for your app. This post about Microcontainers shows you how to build very small images base on Alpine.

UPDATE: the official Docker images are based on alpine now so they are good to use now.