What is the purpose of the layer in the Docker container structure?

A layer in the structure of a Docker container is a separate file layer that contains changes compared to the previous layer. Each layer is created when a command is executed in the Dockerfile (for example, RUN, COPY).

Main features of layers:

• Layers are immutable (read-only).
• Layers are stacked on top of each other, forming the final file system of the container.
• Using layers allows for efficient caching and reuse of parts of the image during building and running.

For example, if you have a base layer with the OS, and the next layer adds an application, then when the application changes, the base layer does not need to be rebuilt.