Re: [squid-users] reverse proxy configuration still MISSes some pages which should be a HIT....

 On Mon, 31 Oct 2011 18:56:00 +0000, Einar Indridason wrote:
> Hi.
>
> I'm using squid 3.1.16, compiled from source with:
> ./configure --prefix=/usr/local/squid-3.1.16/ --enable-useragent-log
> --enable-referer-log --disable-ident-lookups --with-large-files
>
> Running on a 64bit Debian 6 box.
>
>
> If I send a request: Sent by doing: cat file | nc proxy.example.com
> 80
>
> ==============================================================================
> HEAD / HTTP/1.1
> Host: www.example.com
> User-Agent: Mozilla/5.0 (X11; Linux i686; rv:7.0.1) Gecko/20100101
> Firefox/7.0.1
> Accept:
> text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
> Accept-Language: en-us,en;q=0.5
> Accept-Encoding: gzip, deflate
> Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
> Cookie: eplicaWebVisitor=-926431977; fptab=skjalftar;
> JSESSIONID=C44066454BC7A2C8A052BC0C69D44620
> DNT: 1
> Connection: keep-alive
> If-Modified-Since: Sat, 30 Oct 2011 16:42:36 GMT
> Cache-Control: max-age=0
> If-None-Match: S-is-94659-1319906578198
>
>
>
> ==============================================================================
>
> I get back:
>

 Calling this (1) ...

>
> ==============================================================================
> HTTP/1.0 200 OK
> Date: Mon, 31 Oct 2011 18:22:45 GMT
> Set-Cookie: JSESSIONID=05358DBC68CE264A981D34FB8322CADC; Path=/
> Powered-By: Eplica WMS 2.0 (2.0-SNAPSHOT)
> Last-Modified: Mon, 31 Oct 2011 18:22:21 GMT
> Expires: Mon, 31 Oct 2011 18:22:55 GMT
> Cache-Control: public, must-revalidate, max-age=10
> ETag: S-is-94983-1320085375761
> Content-Type: text/html;charset=UTF-8
> Content-Language: is-IS
> Vary: Accept-Encoding
> Content-Encoding: gzip
> Content-Length: 18425
> X-Cache: MISS from proxy.example.com
> Via: 1.0 proxy.example.com (squid/3.1.16)
> Connection: keep-alive
>
>
> ==============================================================================
>

 Calling this (2) ...

> If I send the same request, but leave out the "If-None-Match", I get:
> HTTP/1.0 200 OK
> Date: Mon, 31 Oct 2011 18:24:10 GMT
> Powered-By: Eplica WMS 2.0 (2.0-SNAPSHOT)
> Last-Modified: Mon, 31 Oct 2011 18:23:22 GMT
> Expires: Mon, 31 Oct 2011 18:24:20 GMT
> Cache-Control: public, must-revalidate, max-age=10
> ETag: S-is-94983-1320085460159
> Content-Type: text/html;charset=UTF-8
> Content-Language: is-IS
> Vary: Accept-Encoding
> Content-Encoding: gzip
> Content-Length: 18425
> Age: 3
> X-Cache: HIT from proxy.example.com
> Via: 1.0 proxy.example.com (squid/3.1.16)
> Connection: keep-alive
>
>
> ==============================================================================

 'delta' (time difference) between the two requests is 120 seconds (2
 minutes).

  + Server indicates 'must-revalidate'. Always contact backend server.

  + max-age is 10 seconds. Always fetch new content if current is older
 than 10 seconds.

  + origin servers object was modified 60 seconds after request (1).

 So this is correct. The cached object was stale, backend had an updated
 copy which got returned in full using status 200.

 If-None-Match and If-Modified-Since are both "true" conditions for
 these tests. Either one alone is enough to make a 200 happen.

>
> Hmm... I *think* the needed lines from squid.conf would look like,
> but please correct me if this is not enough to determine the cause:
>
> http_port 1.2.3.4:80 accel defaultsite=www.example.com vhost
> ignore-cc

 The "ignore-cc" directive is there to ignore the client when it tries
 to override the server Cache-Crontrol. In the above your server is
 saying max-age=10 (give clients things up to 10 seconds old). But the
 client is attempting to override and says max-age=0 (nothing 1 second or
 older may be sent to me).
  Since this is a reverse-proxy and your Squid is one of the servers for
 this domain it is able to safely ignore that client max-age, and say
 here is object X, its valid right now (despite being 1-10 seconds old).

 In the case you detailed above, it will make Squid ignore the max-age=0
 (force a reload) from the client. BUT, the server is still indicating 10
 second max-age and must-revalidate. So the revalidate conditions will
 still happen and possibly produce a 200.

>
> cache_peer 1.2.3.99 parent 80 0 no-query originserver name=myAccel
>
>
> Now, is there a simple(ish) way of throwing away / ignoring that
> "If-None-Match" header, or configure squid in other ways, to go to
> the
> cache, and create a HIT?

 That is up to your server to respond with 304 instead of 200. When
 testing conditional requests a 304 message is equivalent to a HIT in
 older traffic.

 As or ignoring the If-* headers. This is a very bad idea(tm)...

 Consider a login script which presents exactly two "variants". One says
 "Successful login". The other says "Successful logout".

 The If-* values and ETag encodes which of these the client is
 attempting to display so Squid and the server can override with 200 and
 essentially say 'no display this instead'.

 In the login example, the server would check its login/out state for
 the client and allow the display or replace it. Overriding these details
 and making Squid "HIT" would lead to users clicking logout buttons and
 seeing "Successful login". Or the opposite; submitting login credentials
 and seeing "Successful logout". Whichever one was cached at the time.

 Things get very messy and confusing for both the users and yourself
 when instead of a clearly visible login/logout message we begin with
 things like media types and encoded stuff. Or even for one more common
 example; someone's list of facebook friends.

 Amos
Received on Mon Oct 31 2011 - 22:33:32 MDT