Geographical Load Balancing

Steven Alligood steve at bluehost.com
Wed Nov 11 15:50:54 MST 2009


On 11/11/2009 03:35 PM, William Attwood wrote:
> On Wed, Nov 11, 2009 at 3:27 PM, Steven Alligood<steve at bluehost.com>  wrote:
>
>    
>> On 11/11/2009 03:19 PM, William Attwood wrote:
>>
>>      
>>> Hello--
>>>
>>>     How does one accomplish geographical load balancing? With that in mind,
>>> what about geographical failover?  Example, I have a data center (DC) in
>>> Dallas, and another in Salt Lake.  How do I re-direct traffic if Dallas
>>> goes
>>> offline?
>>>
>>>     Just a project I'm diving into.  colo-specific load balancing and
>>> failover is accomplished, now we need to protect against the data center
>>> going offline, and speed of access to machines.  I see how I can do
>>> geographical failover with a geographical load balancer, however, do I
>>> need
>>> 2 geographical load balancers if one of them goes offline?
>>>
>>>     Has someone here worked on a project of this magnitude?
>>>
>>>
>>>
>>>        
>> It';s been several years since I have set that up, but the old alteons (now
>> owned by nortel) would do geographical load balancing with one in each
>> location.
>>
>> Basically, you setup your auth dns to point to each location, with any
>> subdomain in DNS delegated to the load balancer.  It would then give out dns
>> based on which one it found to be quicker, etc, and in an outage would give
>> just itself out for it's local farm.
>>
>> Of course, if you are doing IPv6, check out the anycast stuff.  Quite
>> amazing.
>>
>> -Steve
>>
>>      
>
> If one site goes offline, won't that mean 50% of my traffic also goes
> offline, depending on which IP DNS feeds back?  I may have misunderstood
> you.
>
>    
No, the dns for those particular subdomains have very short TTLs (like, 
5 seconds), so they expire quickly and have to be looked up again.  So 
if your site goes down between one web page serve and the next, it gets 
the DNS entry for the site that is still online.



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