What is the purpose of layers in Docker structures and why are they used?

In Docker, layers are separate changes to the filesystem that are overlaid on each other, forming the final container image. Each layer is created when a command is executed in the Dockerfile (for example, RUN, COPY).

Purpose of layers:

• Reuse: if a layer already exists locally, Docker will not recreate it, which speeds up the build.
• Space saving: common layers between images are stored only once.
• Caching: when the Dockerfile is changed, only the modified layers and subsequent layers are rebuilt.

Thus, layers allow for efficient image management, faster builds, and resource savings.