I have several upstream servers, which are configured like this:

upstream backend {
ip_hash;
server backend1.example.com;
server backend2.example.com;
server backend3.example.com down;
server backend4.example.com;
}

each server has ONLY IPv6 address. But seems nginx can't parse it to that address, and report an error like this "[error] host not found".

Is this a bug or meant not to be supported yet?