Isn't that what SRV records are for? If there's one for _http specifying ycombinator.com as the name, then any of those IP addresses should accept a connection

Isn't that what SRV records are for? If there's one for _http specifying ycombinator.com as the name, then any of those IP addresses should accept a connection on port 80 speaking HTTP. Without independent names, they should all be treated equally and your app (like a browser) gets to try just one or all of them. If you're talking about subprotocols/versions of HTTP like HTTP2 then you can define subservices, so you could have _http2._http. But no one has proposed that yet :) Of course with anycast, multiple A records can be redundant :)