I fear you are suffering from misconceptions about how containerization works. It's as if stating that a compiler is invoked every time when a process starts.

Most Docker images consist of multiple superimposed filesystems. When a container is started, a new empty layer is stacked on top which captures all filesystem writes during the container's execution.

This allows the following features:

- After the container stops running, these layers can be combined into a new image. This is what happens when you build images.

- The original image is never changed and can be used at any time to start a new container.

- When a new version of the application is released, it is not necessary to rebuild the whole image from scratch. You just start from the layers below.