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Do you recommend mulitple A Records for WWW servers from different locations with same hostname ?

Posted on 2006-07-05
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Last Modified: 2010-03-19
There was a problem with an ISP last week who provide bandwidth to a customer colo rack.  They are a major ISP who have done a reasonable job in the past.  However, on Friday it took them 8+ hours to resolve a comms peering issue which was stopping about 5% of visitors getting to the WWW servers they were trying to reach.  They temporarily resolved it by restarting their core switches.  They don't yet know what caused the problem.  All I know is that 5% of visitors didn't get to where they needed.

Anyway, I'm now been asked to have their WWW servers available from multiple geographical locations with the same hostname e.g. www.xyzzzzz.com   Someone has suggested multiple A records in DNS as a simple way to achieve this.  The requirement is to keep the networks  separate.  

I need to find out more information on:

Are you similar round-robin-type DNS solutions to provide resilience for your web sites?

Are there standards for how a HTTP client (browser) decides which A record to use ?   Will it make a random choice?

If the IP address of the 1st A record is not reachable do HTTP standards (and browsers) try the 2nd A-name record instead?  

Thanks in advance for any feedback.
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Question by:jon999
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by:Danny_Larouche
Danny_Larouche earned 125 total points
ID: 17042460
The record will be used in a round robin order. if the host failed to respond, the browser will not go to the next one.
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mikeleebrla earned 125 total points
ID: 17042551
danny is correct, but they are VERY slow to do so from my experience so i wouldn't setup multip DNS records a a failover method at all.  The proper way to do this would to be have it handled on the router end, not with DNS records.  IE configure your router to look to the "up" server, no have DNS 'guess' via round robin at which server is up.

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by:GreenfieldIT
GreenfieldIT earned 125 total points
ID: 17043134
are you using any kind of load balancer? we use F5 BigIP as well as global load balancers for DNS records. basically sets records with 0 TTL so that DNS servers must query our DNS load balancers, no local caching
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by:GinEric
GinEric earned 125 total points
ID: 17045184
Go to dnsstuff.com or dollardns.net and see how Yahoo and Microsoft do it with more than one A record for the domain itself.

Once a record is looked up its cached locally, so only the first lookup takes time.

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by:jon999
ID: 17242361
We learnt something from all the posts so the points are shared.  Thanks for your contributions.
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