Dual Web Servers

Kevin Darcy kcd at daimlerchrysler.com
Mon Feb 17 18:21:35 UTC 2003


There's no good way to do this in DNS until all (or at least a vast 
majority of) web browsers support the use of the SRV record type. The 
problems with doing A-record failover are:

a) If you have the name resolve to multiple addresses, then even if you 
always hand them out in a certain order, other nameservers will cache 
the answer and then hand it out to their clients in essentially a random 
order,

b) If you have the name resolve to only the "primary" address, you can 
certainly switch that over to the "secondary" address the instant that 
the primary fails, but if you have a reasonable TTL (an hour or more) on 
your records, then it'll take potentially that long before everyone 
stops going to the old address. You can of course reduce your TTLs to 
unreasonably low values, but that's just bad net.citizenship, because it 
makes your nameservers *and*everyone*else's* overwork under normal 
conditions.

What most people do these days, if they have high reliability 
requirements, is pay significant $$$ for load-balancing solutions from 
telecom companies like Cisco (not that I'm particularly recommending 
their load-balancing products; it just happens to be what we use).

                                                                        
                                    - Kevin

news.orilliapronet.com wrote:

>I want to setup Dual web servers so I have a backup of my web site incase one 
>server is down=2E  What I can't figure out is how to setup DNS=2E  If my webserver 
>is down=2C then the DNS server will still point there=2E  Both would have to be 
>down and my secondary DNS server pointing at the backup Web server for it to 
>work=2E  How would I set this up so if both DNS servers are up but th first web 
>server is down=2C the DNS points to the backup web server=3F
>
>Cheers
>=09=09=09Mark  
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