URLs

Image URLs

Now we are going to inspect the different parts of the URL that you pull. The most common command is something like this, where only the repository name is specified:  

podman inspect ubi8/ubi

 

But, what's really going on? Well, similar to DNS, the podman command line is resolving the full URL and TAG of the repository on the registry server. The following command will give you the exact same results:

 

podman inspect registry.access.redhat.com/ubi8/ubi:latest

 

You can run any of the following commands and you will get the exact same results as well:

 

podman inspect registry.access.redhat.com/ubi8/ubi:latest
podman inspect registry.access.redhat.com/ubi8/ubi
podman inspect ubi8/ubi:latest
podman inspect ubi8/ubi

Now, let's build another image, but give it a tag other than "latest":  

podman build -t ubi8:test -f Dockerfile

 

Now, notice there is another tag
podman images

Notice that podman resolves container images similar to DNS resolution. Each container engine is different and Docker will actually resolve some things podman doesn't because there is no standard on how image URIs are resolved. If you test long enough, you will find many other caveats to namespace, repository, and tag resolution. Generally, it's best to always use the full URI, specifying the server, namespace, repository and tag. Remember this when building scripts. Containers seem deceptively easy, but you need to pay attention to details.