We are removing dependencies on docker types where possible in the core
libraries. credentialprovider is generic to Docker and uses a public API
(the config file format) that must remain stable. Create an equivalent type
and use a type cast (which would error if we ever change the type) in the
dockershim. We already perform a transformation like this for CRI and so
we aren't changing much.
This is step one for cross-region ECR support and has no visible effects yet.
I'm not crazy about the name LazyProvide. Perhaps the interface method could
remain like that and the package method of the same name could become
LateBind(). I still don't understand why the credential provider has a
DockerConfigEntry that has the same fields but is distinct from
docker.AuthConfiguration. I had to write a converter now that we do that in
more than one place.
In step two, I'll add another intermediate, lazy provider for each AWS region,
whose empty LazyAuthConfiguration will have a refresh time of months or years.
Behind the scenes, it'll use an actual ecrProvider with the usual ~12 hour
credentials, that will get created (and later refreshed) only when kubelet is
attempting to pull an image. If we simply turned ecrProvider directly into a
lazy provider, we would bypass all the caching and get new credentials for
each image pulled.
This change refactors the way Kubelet's DockerPuller handles the docker config credentials to utilize a new credentialprovider library.
The credentialprovider library is based on several of the files from the Kubelet's dockertools directory, but supports a new pluggable model for retrieving a .dockercfg-compatible JSON blob with credentials.
With this change, the Kubelet will lazily ask for the docker config from a set of DockerConfigProvider extensions each time it needs a credential.
This change provides common implementations of DockerConfigProvider for:
- "Default": load .dockercfg from disk
- "Caching": wraps another provider in a cache that expires after a pre-specified lifetime.
GCP-only:
- "google-dockercfg": reads a .dockercfg from a GCE instance's metadata
- "google-dockercfg-url": reads a .dockercfg from a URL specified in a GCE instance's metadata.
- "google-container-registry": reads an access token from GCE metadata into a password field.
danielqsj