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DNS CNAME records for DR purpose...

Posted on 2006-07-07
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Last Modified: 2013-12-23
I have an Application running on server1.domain.com. And I have a CNAME for my application as Myapps.domain.com to serverA.domain.com.


Users access the application by using Myapps.domain.com.

I am planning to put a DR for this website on Server2.Domain.com in different city.
Now I want to setup something like MX record priority like…if my Server1.domain.com fails then it should automatically go to my DR server Server2.Domain.com.

How to setup this…Should I put Two CNAME pointing to server1 & server2.

How it is going to work ?



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Question by:moorthy_kulumani
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chris_calabrese earned 500 total points
ID: 17057917
CNAME's are simple one-to-one mappings and not a prioritized mechanism like MX. MX works because the higher-level SMTP software knows how to check if each server is up and running. With CNAME's the resolver library only knows that the name resolved (i.e., the DNS server is up), not whether the actual application/server is up and running.

The way the type of thing you're trying to do is usually done is to have two A records with the same name but differnet IP addresses that point to the two different servers. Then, if one of the servers goes down you can pull its A record (of course you also need really short TTL's or other DNS servers/resolvers will have the bad record cached and not get the update).

You could also have your DNS server check whether each server is up or not on a regular basis (say every 30 seconds) and automagically reconfigure itself.

That's essentially how F5 BigIP and other similar products work (plus fancy GUIs to make it easier to manage, etc.).
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by:moorthy_kulumani
ID: 17070524
Instead of having two A record can i have two CNAME point to Diffent A record with less TTL for the Production ?

And do we need to delete the Prodiction record...when the production server goes down ?

how it is ?
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Expert Comment

by:chris_calabrese
ID: 17072551
No. CNAME's are a one-to-one mapping between a name and another name. A records are one to many mappings between a name and one or more IP addresses.

Yes, you'd need to delete the production record when the production server goes down.
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