Comment 2 for bug 1736920

Already discussed this with Stephen, but for posterity: this bug seems to have been introduced in change Ibc84f159, which was a fix for bug 1557584. We also need to ensure that the fix to this bug doesn't re-break GlanceClientWrapper's retry mechanism.

Ideally, I think we would continue to return an iterator from that method, but we should ensure that at least the initial iteration would hit the retry code. It would be better still if we could switch glance endpoint on hitting a failure half way through a bulk data transfer, but that would require a more substantial change. Glance would have to support partial fetching of an image (does it already?) and we'd have to change the caller to track how much data has been transferred already in case of a failure.

In practice, though, I think it's sufficient that we ensure we're talking to a glance endpoint which is up when we start the transfer. If it goes down during the transfer the operation will fail, which seems acceptable to me.