Motivation: The importance of container image size

Small container images offer the following benefits:

•     Reduced build time
•     Reduced storage space usage
•     Reduced download time
•     Faster deployments
•     Better security due to smaller surface attack

Image layers

To reduce container image sizes, it’s important to understand that container images are composed of multiple layers ( think of them as intermediate images) which form the final image.

At build time, each Dockerfile instruction creates an extra layer.

FROM ubuntu                                            # 4 layers (base image)
MAINTAINER adolfo@orangemonk.net    # 1 layer
RUN mkdir -p /app/bin                              # 1 layer
RUN apt-get install -y wget                       # 1 layer

So, generally speaking, reducing image size is the art of reducing the number of layers.