[CentOS] Load balancing...

[Ryan Ordway]

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.


--
Ryan Ordway                           E-mail: rordway at oregonstate.edu
Unix Systems Administrator               rordway at library.oregonstate.edu
OSU Libraries, Corvallis, OR 97331    Office: Valley Library #4657