Docker: Cannot pull an image that was pushed to a private registry

When you are pulling an image from registry with Docker client, the client will try to send a V2 version request to registry firstly. If this request returned with error (i.e. image not existing or the request is unauthorized), then docker client will fall back and try to send another V1 version request.

Since your registry is on a newer version, and it does not support V1 APIs anymore, the registry will throw error such as 'Unsupported docker v1 repository request' in the second V1 request attempting.

To avoid this, Docker developer is planning to add the --disable-legacy-registry option to Docker client by default. If this option has been set as true, Docker client will not try to send V1 version request again but will return the original error message from initial V2 request.

For more info, please check this issue: https://github.com/docker/docker/issues/26142#issuecomment-271867508