[wplug] OT - request for comment on an idea

[Chester R. Hosey]

On Fri, 2005-06-03 at 14:09 -0400, Chester R. Hosey wrote:
> 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.

I accidentally sent this while still typing.

For issue #2, I'm not quite sure of the best way to ensure continued
service. I'd start with a Google search of "HTTP failover Apache" or
similar.

Good luck.

Chet Hosey