Proposal

If the docker client returns an error during image pull then the command is retried, except for ErrNotFound.

There are more error types defined in https://github.com/moby/moby/blob/master/errdefs/defs.go that are also permanent, as far as I can tell.

I ran into the issue that, with invalid credentials, the pull was retried until I got temp blocked by the container registry. Pulling with invalid credentials should not be tried again.

Suggested errors to be seen as permanent/non-retryable:

• ErrInvalidParameter
• ErrUnauthorized
• ErrForbidden
• ErrNotImplemented

I'm unsure if all types might be returned by ImagePull (e.g. ErrNotImplemented seems unlikely). I also didn't check if there are similar places where the docker client is called within a retry mechanism. If so, it might be worth using a central definition that just contains all permanent types.

Happy to provide a PR if you like the suggestion.