concept image layer in category kubernetes

This is an excerpt from Manning's book Kubernetes in Action, Second Edition MEAP V05. Login to get full access to this book.

Figure 2.8 Containers can share image layers

The figure shows that containers A and B share an image layer, which means that applications A and B read some of the same files. In addition, they also share the underlying layer with container C. But if all three containers have access to the same files, how can they be completely isolated from each other? Are changes that application A makes to a file stored in the shared layer not visible to application B? They aren’t. Here’s why.

This is an excerpt from Manning's book Core Kubernetes MEAP V02. Login to get full access to this book.

The following figure shows a Dockerfile on the top; the two rectangles below display how the layers are created. A Dockerfile is a text definition of the image layers that compose the image. During the build process, layers are stacked in reverse order of the commands in the Dockerfile, so we reversed the command order. The first layer is the last command in the Dockerfile.

Figure 4.1. Container layers

There are a bunch of parts to this puzzle, so a quick recap. Docker is a company, and they support the container community. Containers are the virtual environments created when you run images. The virtual environment is run by a binary that is classified as a container engine. The immutable packaging that supports this architecture is called an image, and an image has layers. To add one more detail to the puzzle, an image layer is simply a tarball.