Docker architecture
As we already know, Docker uses the build once, run anywhere concept. Docker packages applications into images. Docker images form the blueprint of containers, so a container is an instance of an image.
A container image packages applications and their dependencies, so they are a single mutable unit you can run in any machine that runs Docker. You can also visualize them as a snapshot of the container.
We can build and store Docker images in a Docker Registry such as Docker Hub, and then download and use those images in the system where we want to deploy them. Images comprise several layers, so it helps to break images into multiple parts. The layers tend to be reusable stages that other images can build upon. This also means that we don't have to transmit the entire image over a network when we change images and just transmit the delta, which saves a lot of network I/O. We will talk about the layered filesystem in detail later in this chapter.
The...
