On Mar 3, 2011, at 4:25 PM, Ryan Ordway wrote: > On Mar 3, 2011, at 4:12 PM, aurfalien at gmail.com wrote: > >>> Round robin DNS would balance load, but will cause problems if one >>> of >>> them goes down. >> >> Hi Sean, >> >> Can you explain as I may be planning this for a site. >> >> So if I have 2 identical servers, each with there own IP, how will >> one >> of them going down cause issues? >> >> I'm assuming multiple A records for the same host will be handled >> fine >> by the client lookup? > > example.com resolves to: > host1.example.com - A.B.C.D > host2.example.com - W.X.Y.Z > > 1. Client performs DNS lookup and gets pointed to host2. All is well. > 2. host2 goes down. DNS for example.com still resolves to host2, > which is unreachable. Site is down. > > Now, you can work around this by using a HA/failover system like > heartbeat to have host1 and host2 communicating with each other and > if one host goes down the other automatically takes over its IP > address(es) and services. If you have control over your own DNS you > can manage your zone's Time To Live so that records are less > aggressively cached, etc. Yes, I usually have TTL pretty aggressive but you're right. The DNS round robin is more of a poor mans load balancer and probably not appropriate for the OP. - aurf