RH134 II ch13s04 version 9.0 lab question

[chzheng2023]

Lab question 4.2

I wonder why need to add "docker://" as pre-fix for the registry on skopeo inspect command as it doesn't show that on the podman search command output

$ skopeo inspect docker://registry.lab.example.com/ubi8/python-38

 but we can use podman inspect to inspect images without adding "docker://" as pre-fix
$ podman inspectregistry.lab.example.com/ubi8/python-38

What are the differences between these 2 commands?

[zeet · Accepted solution]

Command with Skopeo :

$ skopeo inspect docker://registry.lab.example.com/ubi8/python-38

In this command, docker:// specifies that Skopeo should use the Docker registry protocol to inspect the image located at registry.lab.example.com/ubi8/python-38.

Command with Podman :

$ podman inspect registry.lab.example.com/ubi8/python-38

In this command, the absence of docker:// is because Podman defaults to using the Docker registry protocol when a transport method is not specified. This simplifies the command for common use cases.

Key Differences :

1. Transport Protocol Specification: Skopeo requires an explicit transport protocol (docker://) due to its support for multiple transport methods. Podman defaults to using the Docker registry protocol, simplifying commands for common scenarios.

2. Tool Purpose and Scope: Skopeo is focused on working with container images across various transports and storage locations. Podman is primarily concerned with managing containers and images on a local system, with the ability to pull images from and push images to remote registries.

3. User Experience: Skopeo's requirement for specifying a transport protocol makes it more versatile but also requires a bit more knowledge from the user about where and how the image is stored. Podman's design caters to simplicity and ease of use in everyday container management tasks.

[Travis · Accepted solution]

@chzheng2023 -

So @zeet did a really good job explaining the differences in the commands. However, there is one huge thing that was left out or more likely not emphasized enough ...

podman inspect inspects images locally. So it doesn't need the protocol specified to connect to a remote registry. In order to use Podman to inspect an image it must exist locally on the system.

skopeo inspect can inspect images locally and you don't need the docker:// if you are inspecting one locally on the system, but the SKOPEO command has the ability to inspect and interact with images on a remote registry in which you will want to specify the docker:// in the command.

https://github.com/containers/skopeo

[chzheng2023]

Thank you @zeet and @Travis, your explanations were crystal clear!