What Happens When You Run a Docker Image?

You can run a container from a locally stored Docker image
- If the image does not exist on the system, it is pulled from an online registry

When an image is pulled, the layers are stored independently
When running a container, these layers are stacked in order and mounted at a specific location
By default, the layers belonging to the image are read-only and never change
On top of them, a final container-specific writable layer is added, and all changes that occur in the container are saved to this layer

When running a container, a clean layer is placed on top of the image's topmost layer
No matter how many containers are running, they do not affect each other because the layer where actual writes occur is separated
- In other words, every container has its own unique writable area, which becomes the topmost layer and does not affect any of the lower layers

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