[wplug] OT - request for comment on an idea

[Chester R. Hosey]

On Fri, 2005-06-03 at 13:57 -0400, Chris Romano wrote:

> Now from my understanding if a DNS server can contact the primary DNS 
> of the site/name that it is looking for, it will try the secondary
> DNS 
> for that site/name.  Is this right?  If so, this means that there 
> shouldn't be to much downtime if this where to happen.  I problem is 
> if the IP is cached on the requesting DNS server.  I am not too 
> familiar with DNS yet, so in this case will the site be down until
> the 
> requesting DNS server refreshes it's cache?
> 
> So is there a better way of doing this or am I at least somewhat on 
> the right track?  I hope that I explained that well enough.
> 
> Thanks, 
> Chris

Actually there are two separate parts that you need to worry about:

1) Availability of a DNS server which will translate a domain name to
one or more IP addresses.

2) Ensuring that the services offered by hosts at those addresses fail
over.

Regarding #1, yes, a secondary DNS server should provide this service
should the first one fail. Generally you'd set up the secondary to pull
information from the primary. Since clients can pull from either server
and are likely to cache replies, you cannot expect quick DNS changes to
take effect.

Furthermore, since clients may cache, you cannot have DNS and HTTP on
both servers, simply have DNS for each server reply with its own IP for
the DNS lookup, and expect that DNS failing will cause all clients to
query the other DNS server, get the active server's IP during name
resolution, and connect to the proper HTTP server.

In short, DNS is covered by having a properly configured secondary.

For issue #2, I'm not quite