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Docker image and container relationship

The relationship between Docker images and containers is fundamental to the Docker architecture, functioning similarly to the relationship between object-oriented programming classes and instances^[600-developer__docker__docker.md].

Core concepts

Images are read-only templates (鏡像、模版) used to create containers^[600-developer__docker__docker.md]. Containers are the runnable instances (實例) created from these images^[600-developer__docker__docker.md]. To visualize the relationship: an image acts as a blueprint or class definition, while the container is the actual running object generated from that blueprint^[600-developer__docker__docker.md].

Lifecycle and interaction

When a user executes a command like docker run, the Docker engine retrieves the required image (often from a Docker registry) and initializes a container^[600-developer__docker__docker.md]. A single image can spawn multiple containers, each operating as an isolated process with its own filesystem and namespace, yet sharing the same underlying kernel and image resources^[600-developer__docker__docker.md].

Dependency management

Due to this dependency, specific operational constraints exist. For example, you cannot remove an image using docker rmi if it is currently being used by a container, even if that container is stopped^[600-developer__docker__docker.md]. The container must be removed (docker rm) before the image can be deleted^[600-developer__docker__docker.md].

Sources

^[600-developer__docker__docker.md]