[NTLUG:Discuss] Use DNS for redundant geographic sites?

[Wayne Walker]

The big problems here:

DNS TTL (time to live).  Now you can set this as low as 5 minutes.  it
increases the load on your DNS servers, but then you only have a 5
minute window before all other DNS requestors are _Supposed_ to ask for
the address again.

BROWSERS - almost all browsers cache the IP that they get for a host
name FOREVER.  Forever meaning the entire life of that browwser process.
SO if a user brings up a browser and goes to your site and then lreaves
their browser running for 10 weeks, then for 10 weeks they will use the
same address and never do another DNS lookup of your host...   :(

If instead you start with DNS handing out a set of IPs for thw host www,
then the browser should cache the set and if one goes down, will use
another without any problems at all.  I've not tested this...but believe
it's true.  

Wayne

On Sun, Nov 19, 2006 at 10:52:47PM -0600, Neil Aggarwal wrote:
> Hello:
> 
> I am trying to figure out a way to create a web site
> that is multi-homed geographically.
> 
> I just thought of this idea:
> 
> I will have two machines, each located in
> a different place.
> 
> Machine A will run:
> 	dnsA.jammconsulting.com (DNS server)
> 	webA.jammconsulting.com (Web Server)
> 
> Machine B will run:
> 	dnsB.jammconsulting.com (DNS server)
> 	webB.jammconsulting.com (Web Server)
> 
> Now, lets assume that I register a new domain
> name.  For discussion, lets use jammconsulting.com
> as the domain name.
> 
> In the domain records, I set the DNS servers to
> be:
> 	dnsA.jammconsulting.com
> 	dnsB.jammconsulting.com
> 
> Now, here is the strange part:
> 
> dnsA will always resolve www.jammconsultng.com to 
> the IP address of webA and dnsB will always resolve
> www.jammconsulting.com to the IP address of webB.
> 
> This way, if either machine goes down, the machine
> will not respond to DNS queries.  The DNS will query
> the other machine and all traffic will go to it.
> 
> I know this does not protect me against the situation
> where dnsA is up and webA is down, but as long as
> the machine is up, I can set up monitoring of the
> web server.  Usually, Apache httpd runs without a
> problem.
> 
> Will DNS clients handle a situation where the 
> nameservers give different responses?
> 
> Are there other downsides I have not considered?
> 
> Thanks,
> 	Neil
> 
> --
> Neil Aggarwal, (214)986-3533, www.JAMMConsulting.com
> FREE! Eliminate junk email and reclaim your inbox.
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> 
> 
> _______________________________________________
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-- 

Wayne Walker

www.unwiredbuyer.com - when you just can't be by the computer

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