Summary

In this post, we will discuss diffrent tyeps of image id displayed in the result of docker inspect ${image_id}

All operations related to docker are based on docker version > v1.10

Layer ID

Layer in RootFS is a fundamental mechanism of dockers, which enables sharing the same basic image layer in diffrent built images.

Each layer has its parent layer and a unique id generated by hash digest algorithm based on the content in this layer.

Image Id

Before docker v1.10, the image id will simply be same with the id of the top layer. Same as parent field.

Since docker v1.10, images and layers are no longer synonymous. Layers are now identified by a digest, which takes the form algorithm:hex;

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sha256:831c5620387fb9efec59fc82a42b948546c6be601e3ab34a87108ecf852aa15f

Layers no longer belong to images. They are merely collections of files and directories.

Right now, image id is now identified by a digest, which takes the form algorithm:hex. It’s a computed SHA256 hash of the image configuration object which is the metadata of certain image.

Distribution Id in Registry

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docker push custom/cluster-manager:1.0.1
The push refers to a repository [docker.io/custom/cluster-manager]
f22bfascdf82: Pushed 
5f7aaf18da86: Layer already exists 
4d12ab9015d4: Pushed 
latest: digest: sha256:7f63e366abf377e2658e458ea1f6d5e002ff0cfd9ff28307hfc1b45aea2f820 size: 6128

When a image is pushed to a registry, docker daemon will compress the image for network efficiency and a manifest will also be created containing the contents of the image and digests of the compressed layer content.

The digest of a compressed image can be referred to as a distribution digest.

References

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https://windsock.io/explaining-docker-image-ids/