Use constructor for ecrProvider
Rename package to "credentials" like golint requests
Don't wrap the lazy provider with a caching provider
Add immedita compile-time interface conformance checks for the interfaces
Added comments
This is step two. We now create long-lived, lazy ECR providers in all regions.
When first used, they will create the actual ECR providers doing the work
behind the scenes, namely talking to ECR in the region where the image lives,
rather than the one our instance is running in.
Also:
- moved the list of AWS regions out of the AWS cloudprovider and into the
credentialprovider, then exported it from there.
- improved logging
Behold, running in us-east-1:
```
aws_credentials.go:127] Creating ecrProvider for us-west-2
aws_credentials.go:63] AWS request: ecr:GetAuthorizationToken in us-west-2
aws_credentials.go:217] Adding credentials for user AWS in us-west-2
Successfully pulled image 123456789012.dkr.ecr.us-west-2.amazonaws.com/test:latest"
```
*"One small step for a pod, one giant leap for Kube-kind."*
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.
k8s-merge-robot