What is the difference between a digest and an image ID?

What is the difference between a digest and an image ID?

• A. A digest is a checksum taken from a container registry, while an image ID is a checksum based on the local container image
• B. A digest and an image ID are the same thing
• C. A digest is a local checksum; image ID is a registry checksum
• D. An image ID is a tag used to distinguish image versions

Answer: (A)

The key idea is that a digest refers to the exact image content as stored in a container registry, while an image ID refers to the exact image as stored locally on a host. A registry digest is a checksum of the image manifest (and its config) in the registry. It uniquely identifies that specific image content in a registry and stays tied to that content when you pull or reference it from everywhere the registry serves. An image ID is the local, host-specific checksum for the image as seen by the container runtime. It’s derived from the local image’s layers and metadata, so it can differ between hosts or after rebuilding, even for the same registry image. So the statement that a digest is a checksum from the registry and an image ID is a checksum based on the local container image fits the roles these identifiers play. The other options misrepresent the relationship or refer to tags, which are separate labeling, not the actual content-identifying checksums.

The key idea is that a digest refers to the exact image content as stored in a container registry, while an image ID refers to the exact image as stored locally on a host.

A registry digest is a checksum of the image manifest (and its config) in the registry. It uniquely identifies that specific image content in a registry and stays tied to that content when you pull or reference it from everywhere the registry serves.

An image ID is the local, host-specific checksum for the image as seen by the container runtime. It’s derived from the local image’s layers and metadata, so it can differ between hosts or after rebuilding, even for the same registry image.

So the statement that a digest is a checksum from the registry and an image ID is a checksum based on the local container image fits the roles these identifiers play. The other options misrepresent the relationship or refer to tags, which are separate labeling, not the actual content-identifying checksums.