The problem/use-case that the feature addresses

When hostnames are used, redis-cli is not capable of setting up a cluster using only hostnames. Originally reported in this comment by @liuchong.

Description of the feature

Support CLUSTER MEET hostname port (do DNS lookup in Redis)

Alternatives you've considered

Let redis-cli do the DNS lookup.

Additional information

Thanks to hiredis, redis-cli can already connect using hostnames, but that's implicitly handled by hiredis.

DNS lookup already implemented in anetResolve() which is used by Sentinel. It would only take a few lines to add it, but tests might require hostnames with DNS records. This is regardless of if we add it to redis-cli or Redis itself.

In #9530 DNS lookup in Redis is listed as "Out of scope". A benefit of doing the DNS lookup in Redis (rather than in redis-cli) is that we can implement TLS SNI/SAN validation for the cluster bus later. That might require more changes though since the hostnames are not currently gossiped.

@madolson Would you prefer DNS lookup to happen in redis-cli or in CLUSTER MEET?