Comment by Terretta

TL;DR:

Applications should not use getaddrinfo(). Because for the connect by name, the OS or app SDK can parallelize the entire multi-step lookup and connection process, not just step by step:

“Now, I’m not saying that all implementations of these APIs [Java, Apple Foundation, etc., doing connect by name] necessarily do the right thing today, but if applications are using these APIs, then the implementations can be improved over time.”

“The difference with getaddrinfo() and similar APIs is that they fundamentally can’t be improved over time. The API definition is that they return you a full list of addresses, so they have to wait until they have that full list to give you. There’s no way getaddrinfo can return you a partial list and then later give you some more.”

The deck's position on implementation of happy-eyeballs (which could sound dismissive here but is treated as "you had one job" important by the deck), is finding a way to avoid waiting 5 seconds for either side of IPv4 vs. IPv5 stack to timeout before finishing connection setup and serving the user a web page.