This is the kind of book I'd like to see more of. Short and specific to a single area. I've used Docker before but there's extra detail here I wouldn't have known from just using it.

Docker and containerisation is a step up from virtualisation, instead of creating a whole mini machine like you do with a Virtual Machine, the containers ontop of Docker borrow from the host operating system so it's more lightweight than VMs.

Docker images are layers of files, potentially a single layer could be updated and then when syncd up to the Docker Hub repository only the layer changed could be updated.

Docker Swams are new to me.