newbie DNS question

[D. Taylor]

Interesting solution, but you might consider the following
using TTL.

Joel, do you control your DNS?  If so, you could have something
monitor your primary (192.168.100.1), and if it goes down, change
the DNS files as appropriate and HUP named.  What you would want
for your entry most of the time is:

www    300   IN  A  192.168.100.1

This puts a 300 second TTL on the www RR.  If 192.168.100.1 goes
down, and your script changes the above entry to

www    300   IN  A  192.168.100.2

then clients which have cached the first DNS RR will (should)
experience an outage of about five minutes.  After five minutes
they will (should) discard the cached 192.168.100.1 RR, perform
a DNS query, and get the new 192.168.100.2 RR.

Note:  You can make the TTL whatever you want, but the shorter
the TTL the heavier the load on your nameservers (ie, clients
will (should) not cache the entries for longer than the TTL,
and thus have to (should) query the nameserver more often).

For a more robust solution, make a new box, 192.168.100.10,
install mod_rewrite, and have it redirect all requests to
192.168.100.1 (or 192.168.100.2 if 192.168.100.1 is down).


D


On Thu, 16 Mar 2000, Mike Sheldon wrote:

> Date: Thu, 16 Mar 2000 11:37:08 -0700
> From: Mike Sheldon <msheldon@desertraven.com>
> Reply-To: plug-discuss@lists.PLUG.phoenix.az.us
> To: plug-discuss@lists.PLUG.phoenix.az.us
> Subject: RE: newbie DNS question
> 
> Yes and no.
> 
> You can't specify a true preference rating, but you can use the round-robin
> to favor a particular server.
> 
> ie:
> 
> www	IN	A	192.168.100.1
> www	IN	A	192.168.100.1
> www	IN	A	192.168.100.2
> 
> Will send 2 of every three requests to 192.168.100.1 when www.yourdomain.com
> is requested. The downside is that if one of the servers is down, the
> browser that gets that entry will not move to the next entry.
> 
> At this time, a true load-balancing/fail-over solution requires an
> intelligent router or a fail-over solution on the web servers.
> 
> Michael J. Sheldon
> Internet Applications Developer
> Phone: 480.699.1084
> http://www.desertraven.com/
> PGP Key Available on Request
> 
> -----Original Message-----
> From: plug-discuss-admin@lists.PLUG.phoenix.az.us
> [mailto:plug-discuss-admin@lists.PLUG.phoenix.az.us]On Behalf Of Joel
> Dudley
> Sent: Thursday, March 16, 2000 10:51
> To: plug-discuss@lists.PLUG.phoenix.az.us
> Subject: newbie DNS question
> 
> 
> I was wondering if there was a way to set up preferences for web sites in
> DNS much like you set preferences for mail servers.  Say I have a site
> running simultaneously on a Dell poweredge and a backup of it running on a
> Compaq proliant.  I always want to use the dell to host the site, but if the
> Dell goes down I want DNS to recognize this and begin using the Compaq to
> serve the site with the backup.   Is it possible to do this in DNS, or is
> there another way to do this.  Maybe with virtual domains in Apache.  Thanks
> in advance for help on a newbie question.
> 
> - Joel
> 
> 
> 
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