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302 redirections and base url

From: <danielh@econ.ag.gov>
Date: Sat, 24 Jan 98 18:45:29 -0500
Message-Id: <199801250011.TAA08279@www10.w3.org>
To: www-talk@w3.org
I have a question about possible mechanisms of informing a user-agent as
to the base-url of a future stream of requests.  Please forgive any
non-standard terminology....

** The problem:

A simple, yet quite flexible, means of load balancing is for a server at a
"main site"  to use 302 responses to redirect requests to a set of  
"subsidiary servers".   In fact, it is possible for this  "main site" to
track load on these subsidiary servers, and use this near-real-time
information to dynamically adjust the frequency of redirections (I've done
this on an os/2 based server)

As compared to DNS (or other) mode of redirection, this method has one 
drawback: relative URL's on the "subsidiary" servers will point back to
the subsidiary server.  Thus, subsequent requests will be "locked" on this
subsidiary server. This locking can reduce the efficiency of the load
balancing, since the main site (the one with all the information) will not
have a chance to select which site future requests  (from  this client)
should be "redirected" to.

<Of course, in some cases this "locking" may be good -- since you only
need one redirection per session. But in other cases it's not good, as
when cpu  intensive requests (i.e.; cgi- scripts) are frequent, and when
the capacities of the various sites vary>

** Possible solutions:
Of course, one can always use absolute URLs in HTML documents on the
subsidiary sites. Or, <BASE href="main_site"> URL's could be used in the
 Or, under http 1.1, a  content-base response header could be added.

But these solutions are less then perfect;  i.e.; they require tinkering
with (perhaps a multitude) of files on each subsidiary server. 

** A suggestion (or does such a mechanism exist)?

Is there some way for an origin server (say, with a special response
header) to inform a user-agent to redirect the request to a new
location; BUT, to use the "current location" (of this origin server) as
the "base-URL"?  

Received on Saturday, 24 January 1998 19:11:25 UTC

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