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Re: mirrorlist cgi



On Mon, 2006-07-17 at 21:43 -0400, seth vidal wrote:
> On Tue, 2006-07-18 at 02:31 +0100, Andy Burns wrote:
> > seth vidal wrote:
> > 
> > > Where would you like to place the magical no-single-points-of-failure
> > > router?
> > 
> > :-)
> > 
> > Use round-robin DNS for mirrors.fedoraproject.org resolving to 
> > geographically dispersed servers?
> 
> and if one of the servers fail then 1 out every N dns requests fail to
> find the host b/c the resolving host is down.
> oh - but you say - have the dns tables get updated so if a host goes
> down it gets taken out of the search? That's why dns caching (yes,
> despite TTLs) sucks.
> 

If the server has multiple DNS aliases and then the client can be
written to fetch multiple aliases in a single DNS request and try
several before giving up.

The client could also cache a copy of the mirror list to fall back. I
imagine the client could even try a couple of servers from the previous
cached list before contacting the central server for a refresh (which
could reduce the load on the server hosting the mirror list).


The even better solution is to have multiple dispersed servers with the
_same_ IP. This can be done for UDP using IP Anycast but isn't suited to
TCP/HTTP traffic since sequential packets can get sent to different
servers.
 http://www.net.cmu.edu/pres/anycast/
 http://en.wikipedia.org/wiki/Anycast 


	Jon



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