Hi,
If a DNS name is setup with multiple IPs (A records) in a round-robin set, and the DNS server returns all the IPs, does iOS networking libraries try each of the IPs until they find one that it can connect? It appears many browsers and other network clients like curl are able to do this already.
https://blog.engelke.com/2011/06/07/web-resilience-with-round-robin-dns/
Any other details/pointers to documentation or code on this are greatly appreciated.
Apple platforms have a connect-by-name infrastructure that intelligently handles servers with multiple IP addresses, supporting arbitrary mixes of both IPv4 and IPv6. The exact mechanics of this has changed over time. This post describes the approach used by OS X 10.7 (equivalent to iOS 5), but keep in mind that things have moved on a bit since then.
If you’re creating software for Apple platforms the take-home message is that you should use a high-level API that takes advantage of this connect-by-name infrastructure. That means CFSocketStream or anything layered on top of that, most notably, NSURLSession.
If you don’t use these high-level APIs then you have extra work to do. At a minimum you must use a DNS API that supports IPv4 and IPv6 (typically
getaddrinfoIf you’re looking for advice on how to set up your server’s DNS, I’m not really the right person to answer that. However, my expectation is that naïve approaches like round-robin DNS will provide no significant gain to any modern Apple clients.
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