Container Images

What’s an Image

• App binaries and dependencies

• Metadata about the image and how to run the image

• Official definition: “An image is an ordered collection of root filesystem changes and the corresponding execution parameters for use within a container runtime”

• Not a complete OS. No kernal, kernal modules (e.g. drivers)

• Small as one file (your app binary) like golang static binary

• Big as Ubuntu distro with apt, and Apache, PHP, and more installed

Image and Their Layers

• Images are made up of file system changes and metadata

• Each layer is uniquely identified and only stored once on a host

• THis saves storage space on host and transfer time on push/pull

• A container is just a single read/write layer on top of image

• docker image history and inspect commands can teach us