It still depends, and it's a combination of two behaviors: (1) what a browser's resolver does when it receives multiple A/AAAA records, with some selecting the

It still depends, and it's a combination of two behaviors: (1) what a browser's resolver does when it receives multiple A/AAAA records, with some selecting the first unconditionally and forcing authoritatives to play spin-the-data and (2) failure behavior, both between timeouts and positive failures -- the difference between layer 3, 4, and 7 failures also comes into play. What happens if the connection resets after a single byte? What happens if a positive refusal comes back? What happens with a warm cache for the domain? etc. etc. The failure matrix explodes very quickly, and I seem to recall there being several hundred scenarios to test last time I looked into this seriously. Last time I researched this, behavior was quite different across the board, and it's something one should test extensively when designing HA for HTTP. In some situations, the same browser on another platform will defer to the system resolver versus its own, for example, which will potentially change behavior #1 even for the same browser. Mobile is starting to perform weird tricks with TCP, too, so you really have to dig into this one to do it right. Then throw in HTTP/2 and you've magically created yourself about a decade of justifiable work ;)