[j-nsp] Anycast

[Wojciech Owczarek]

Johan,

As Frank hinted - I think GeoIP-based anycast DNS would be a much better solution here, basically if you can afford it you could use Akamai DNS anycast - there is also GeoDirector which I think is free - or try using BIND with GeoDNS patch yourself, but that's if you host your own DNS. You *could* use IP anycast but this would require session and DB replication to be 100% reliable, which can be tricky without using application load balancers like F5 or Radware, and the longer distances (latency) between sites, the worse it gets. With a DNS-based "geocast" solution, you could make do with DB replication only. That's if location is good enough a criterion for you to base the balancing on.

Regards,
Wojciech

-
Wojciech Owczarek



On 18 Jan 2011, at 19:58, Frank Sweetser <fs at WPI.EDU> wrote:

> On 1/18/2011 1:45 PM, Johan Borch wrote:
>> Hi,
>> 
>> This is not a specific Juniper question, but there seems to be a lot for
>> knowledge on this list so I will give it a shoot :)
>> 
>> Would web traffic be suitable to use with anycasting? The applications in
>> question is a standard website with database backend that I need to load
>> balance (active-active) between multiple sites. I've never worked with
>> anycast before but as I understand it the anycast-part is merely me
>> announcing the server addresses from multiple sites in my IGP?
> 
> Short answer: no, it's not suitable.
> 
> Anycast doesn't give you any guarantees that all packets in a given TCP session will go to the same server.  This isn't typically an issue in the case of DNS, where a) traffic is typically single packet queries and single packet answers and b) all servers will give the same answer to a given client.  With HTTP traffic, though, you have no guarantee that the client packets won't get routed to a different server halfway through the request.
> 
> In the long run, you'll be much happier just getting a product designed to handle your needs, like an F5 or A10 load balancer.
> 
> -- 
> Frank Sweetser fs at wpi.edu  |  For every problem, there is a solution that
> WPI Senior Network Engineer   |  is simple, elegant, and wrong. - HL Mencken
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