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DNS multiple A records/CNAME query

Posted on 2010-08-26
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Hello

We are running Windows 2003 AD DNS - domain is company.com

We have a web application that we want to be accessed on http://webapp.company.com

The actual application will be running on two Windows 2003 Servers - server1.company.com and server2.company.com

Does anyone know how I can make "webapp.company.com" point to both servers (for load balancing)?

Do I:

i. Create an A record for 'webapp' have it point to the IP addresses of server1 and server2

ii. Create a CNAME entry of 'webapp' for the A records of server1 and server2?

iii. Something else?

Also - do I need to make the PTR records point back to 'webapp'?

Secondly, I would also like to implement some sort of fault tolerance here. So that if, say, server1 was down, all requests would go to server2.

iv. Am I correct in thinking that the solution I implemented for DNS load balancing above would not help? Even if a server was down, DNS would still return either address for requests?

v. What I need is a load balancer (Cisco etc)?
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Question by:Joe_Budden
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anomiagrunge earned 2000 total points
ID: 33537425
You should use Network Load Balancing.
You publish your webapp on the virtual ip of the cluster an all the balancing and the failover works automatically.
Start by reading this: http://technet.microsoft.com/en-us/library/cc758834%28WS.10%29.aspx

Hope it helps

Ariel
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by:Joe_Budden
ID: 33537443
Thanks!

Out of interest, if I only wanted to use DNS round robin, how would this work in terms of the DNS entries (questions i and ii)?
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Expert Comment

by:Mike Thomas
ID: 33537469
It won't really afaik, you need to configure load balance or cluster failover.
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Expert Comment

by:anomiagrunge
ID: 33537480
In that case, just configure 2 A records with the same name pointing to the different servers. It only will balance the load on a 50-50 basis.
Be aware also that if your app keeps session of the client, you need to maintain it and that can´t be done with DNS.  
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by:Joe_Budden
ID: 33537508
Thanks - so for purely round robin, I couldn't do any of these:

i. Create an A record for 'webapp' have it point to the IP addresses of server1 and server2

ii. Create a CNAME entry of 'webapp' for the A records of server1 and server2?

I would need to create two seperate A records, and have each one point to the IP's of server1 and server2?
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Expert Comment

by:anomiagrunge
ID: 33537614
You can´t create an A record pointing on 2 addresses. The only way is to create 2 separate A records with the same name pointing to each server
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by:Joe_Budden
ID: 33537636
Thanks...

What is wrong with (ii) [the CNAME idea] too? Just so I know the reason I am wrong :)
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Expert Comment

by:anomiagrunge
ID: 33537702
You can also do the same i told you with CNAME´s. It´s the same.

Regards!
Ariel
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