What happens when a container starts?

When a container starts, Docker takes an image and creates an isolated process from it. The sequence of steps at the junior level looks like this:

#1. Docker takes the image

An image is a template (layers with a file system and configuration). It is the foundation of the future container.

#2. A writable layer is created

On top of the image layers, Docker adds a changeable layer, where all the container's changes (logs, temporary files, and so on) will go.

#3. The container gets isolated resources

Docker configures namespaces and cgroups so that the container:

• sees only its own processes,
• has its own file system,
• has its own network environment,
• can use limited resources.

#4. The main process starts

Docker runs the command specified in CMD or ENTRYPOINT in the image. This process = "the container's life".

#5. The container runs as long as the process lives

If the process ends, the container stops automatically.

#Summary in one phrase

When a Docker container starts, an isolated environment is created from the image, a writable layer is added on top, and the main process starts, on which the container's life depends.

If you want, I can break down the same chain at the middle level (with details about OverlayFS, the PID namespace, the network namespace, and so on).