Looking to implement "If modified since" between browser and varnish cache

[Ask Bjørn Hansen]

On Sep 30, 2010, at 20:06, Indranil Chakravorty wrote:

> I have been mulling over the feasibility of implementing conditional requests between the client browser and varnish cache. 

You are in luck - that already works. :-)

And yes - all common browsers support this.  You can combine a short-ish Cache-Control maxage header with a longer cache time in Varnish to get some control of how long content is cached for.


 - ask

First request (get Last-Modified for the next request) ============

[ask at embla ~]$ curl -svo/dev/null http://www.pool.ntp.org/en/
* About to connect() to www.pool.ntp.org port 80 (#0)
*   Trying 207.171.3.6... connected
* Connected to www.pool.ntp.org (207.171.3.6) port 80 (#0)
> GET /en/ HTTP/1.1
> User-Agent: curl/7.19.7 (universal-apple-darwin10.0) libcurl/7.19.7 OpenSSL/0.9.8l zlib/1.2.3
> Host: www.pool.ntp.org
> Accept: */*
> 
* HTTP 1.0, assume close after body
< HTTP/1.0 200 OK
< Server: Apache/2.2.3 (Red Hat) mod_apreq2-20051231/2.6.1 mod_perl/2.0.4 Perl/v5.8.8
< X-UA-Compatible: IE=8
< P3P: CP="NOI DEVo TAIo PSAo PSDo OUR IND UNI NAV", policyref="/w3c/p3p.xml"
< Last-Modified: Fri, 01 Oct 2010 04:13:06 GMT
< Vary: Accept-Encoding
< Keep-Alive: timeout=30, max=100
< Content-Type: text/html; charset=utf-8
< Content-Length: 14214
< Date: Fri, 01 Oct 2010 04:14:27 GMT
< X-Varnish: 946925222 946924396
< Age: 81
< Via: 1.1 varnish
* HTTP/1.0 connection set to keep alive!
< Connection: keep-alive
< X-Served-By: ntplax2.ntppool.net
< X-Cache: HIT
< X-Cache-Hits: 298
< 
{ [data not shown]
* Connection #0 to host www.pool.ntp.org left intact
* Closing connection #0


IMS request ==============


[ask at embla ~]$ curl -H 'If-Modified-Since: Fri, 01 Oct 2010 04:13:06 GMT' -svo/dev/null http://www.pool.ntp.org/en/
* About to connect() to www.pool.ntp.org port 80 (#0)
*   Trying 207.171.3.6... connected
* Connected to www.pool.ntp.org (207.171.3.6) port 80 (#0)
> GET /en/ HTTP/1.1
> User-Agent: curl/7.19.7 (universal-apple-darwin10.0) libcurl/7.19.7 OpenSSL/0.9.8l zlib/1.2.3
> Host: www.pool.ntp.org
> Accept: */*
> If-Modified-Since: Fri, 01 Oct 2010 04:13:06 GMT
> 
< HTTP/1.1 304 Not Modified
< Date: Fri, 01 Oct 2010 04:14:31 GMT
< Via: 1.1 varnish
< X-Varnish: 946925256
< Last-Modified: Fri, 01 Oct 2010 04:13:06 GMT
< Vary: Accept-Encoding
< Connection: keep-alive
< X-Served-By: ntplax2.ntppool.net
< X-Cache: HIT
< X-Cache-Hits: 313
< 
* Connection #0 to host www.pool.ntp.org left intact
* Closing connection #0