Location of the local copy of Docker's registry manifest-file

Question

Looks like a Docker image has two manifests. One is local, that is saved as a part of docker save, for example, and a different one that is generated when the image is being pushed to Docker registry.

So, my question is there a way to find this registry manifest file? Is it stored somewhere locally? Maybe inside the Docker.qcow2 image?

Answer 1

Today's Docker engine uses the manifest as a guide to determine what other content (layer blobs) to download during a docker run where the image is not local or docker pull. However, it does not store the manifest as JSON in a local cache that I'm aware of, leaving you without an easy spot to go get the actual registry's manifest.

Two things that may be of interest:

1. We are in the process of adding a new docker manifest command for direct interaction with the manifest object that may be of interest to what you are trying to do.
2. This is mostly to support the "manifest list" v2.2 spec type that supports multi-platform images, based on the manifest-tool work I did originally to create and query manifests from a registry.

However, if those two bits of code/projects aren't directly useful, you may be able to hack one or both of them to just dump a registry manifest JSON object pretty easily.