What is a Docker image and what is a container?

What is a Docker image and what is a container?

• A. Image is a running process; container is a file system snapshot
• B. Image is a static template; container is a runnable instance built from an image
• C. Container is a storage volume; Image is a static template
• D. Image is a network policy; container is a storage volume

Answer: (B)

At the heart of this distinction is that a Docker image is a static blueprint, while a container is a runnable instance created from that blueprint. The image bundles the app code, its dependencies, and configuration in a read-only, shareable template. It’s immutable and can be versioned, built from a Dockerfile, and stored in registries so others can pull it. A container, on the other hand, is the live runtime created from an image. It has its own writable layer on top of the image, its own network and process namespace, and it can be started, stopped, paused, or removed. Multiple containers can run from the same image, each with its own state and data, but all sharing the same underlying image template. That’s why this option is the best match: the image is a static template, and the container is the runnable instance built from that image. The other descriptions mix up roles (for example, treating an image as a running process or a container as a storage volume), which isn’t how Docker concepts work.

At the heart of this distinction is that a Docker image is a static blueprint, while a container is a runnable instance created from that blueprint. The image bundles the app code, its dependencies, and configuration in a read-only, shareable template. It’s immutable and can be versioned, built from a Dockerfile, and stored in registries so others can pull it.

A container, on the other hand, is the live runtime created from an image. It has its own writable layer on top of the image, its own network and process namespace, and it can be started, stopped, paused, or removed. Multiple containers can run from the same image, each with its own state and data, but all sharing the same underlying image template.

That’s why this option is the best match: the image is a static template, and the container is the runnable instance built from that image. The other descriptions mix up roles (for example, treating an image as a running process or a container as a storage volume), which isn’t how Docker concepts work.