Caching doubt

Jonathan Leibiusky ionathan at
Mon Sep 6 16:40:01 CEST 2010

I'm playing with If-None-Match and Cache-Control: max-age   headers and I
have a doubt. Maybe it is more related to HTTP than Varnish, but it worth

Imagine that I have 3 user-agents, a varnish and my webserver.
When the clients ask the first time for /example, varnish doesn't have
anything cached so he ask the webserver for it. The webserver response has
Cache-Control: max-age=180 and ETag: 123 (for example).
So Varnish will cache the response for 180 seconds as well as the
After 180 seconds, the 3 user-agents will request /example for a conditional
If-None-Match header because they got the ETag. Since it is a conditional
request varnish will ask the webserver and will get a fresh response with
all the caching headers. When the other 2 user-agent make the same
conditional request they will generate another request to the webserver
unless varnish has some mechanism to answer himself.
Is that right? Does varnish has this mechanism?


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