[Server-devel] Reverse proxies on the XS (was: Re: Everex gpc mini - an option for the XS?)

Ivan Krstić krstic at solarsail.hcs.harvard.edu
Thu Mar 6 14:42:19 EST 2008

On Mar 6, 2008, at 7:58 PM, Sameer Verma wrote:
> I'd imagine Varnish would help with speeding things up on the Moodle  
> side. Is this correct?

It's an insufficiently specific question:

* For making sure pages previously visited within a session by the
   same logged-in user do not require network retransmission, web
   applications should issue HTTP-standard expiration dates and
   validator headers. Standards-compliant browsers will obey these
   without the need for a reverse proxy to sit in front of Apache.

* If the web application has expensive-to-generate pages whose
   contents do not vary often or by user but are regenerated on each
   hit, it's doing something wrong. Putting a reverse proxy in front
   of it will mask the brokenness, but the behavior is still broken
   and the web application should fix it.

* If the web application has expensive-to-generate pages that do vary
   by user (e.g. have an indication of which user is logged in or any
   other per-user customization), a reverse proxy won't help unless
   the application emits ESI markup and the revproxy obeys it. I bet
   Moodle doesn't, and virtually none of the small proxies support ESI
   anyway. Varnish has partial support that's not production-quality.

Ivan Krstić <krstic at solarsail.hcs.harvard.edu> | http://radian.org

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