On Thu, 2012-05-17 at 00:13 +0800, Ed Greshko wrote:
when you do a look up on www.cnn.com it will return 4 IP addresses. Now, since bind would have that in its cache it wouldn't have to send out a query. What I don't know is if an application would make a request would the list be returned in the same order every time to the requesting application? In other words, if the TTL is not set low, would that defeat the round robin technique.
Unfortunately, there is no guarantee that a client resolver will actually use the IP addresses in the order they are presented by the DNS server. Nothing in the DNS spec requires them to do so.
Interesting things to investigate.....if I really had the time.
My experience says that DNS round robining is actually a poor method of load balancing. I'm surprised to see a large site like CNN resorting to this (if that's really what they are doing this for). Perhaps in combination with a low TTL and a modified DNS server, they can send out a completely different set of IPs every few minutes, and achieve a sort of crude load balancing that way, but I think load balancing works better if you just send out a single IP and use a load balancer that you can control, such as LVS (Linux Virtual Server) that can farm out incoming connections to a single virtual address out to multiple real addresses.
--Greg