When making a HEAD request, use the bucket vhost.
When making a HEAD request, use the bucket vhost.

https://forums.aws.amazon.com/thread.jspa?messageID=340398 explains
why: a HEAD request to a location-specific bucket will get a 301
redirect that doesn't include enough info to actually redirect. The
intent is to prompt the client to use the vhost. So use a vhost
pre-emptively on HEAD requests.

borodust/zs3