Problems encouraging caching on the browser

Question

We are a web-hosting site and we have an iRule setup to encourage caching on the client browsers.  However, a lot of URIs that meet the iRule arguments are not being cached by clients running IE6.0.  A specific URI that we are having trouble with is:&nbsp;
&nbsp;/imageserver/plumtree/common/private/js/jsutil/LATEST/PTUtil.js&nbsp;
&nbsp;Please let me know is there are any other considerations for this work.  Some smaller files seem to be cached, but I know my cache limit is not the problem.  Please let me know if you have any ideas.&nbsp;
&nbsp;The iRule is:&nbsp;
&nbsp;when HTTP_REQUEST priority 50 {
&nbsp;    set cachetime 0&nbsp;
&nbsp;    if {not ([HTTP::version] equals "1.1")} {
&nbsp;      HTTP::header insert "x-httpversion" [HTTP::version]
&nbsp;      log local0. "Access via [HTTP::version]"
&nbsp;    }
&nbsp; 
&nbsp;  switch -glob [string tolower [HTTP::path]] {
&nbsp;    "/imageserver/plumtree/common/*" -
&nbsp;    "/imageserver/plumtree/portal/private/*" -
&nbsp;    "/imageserver/plumtree/portal/public/*" {
&nbsp;       set cachetime $::twoweeks
&nbsp;    }
&nbsp;    "/imageserver/plumtree/portal/custom/*" {
&nbsp;       set cachetime $::workday
&nbsp;    }
&nbsp;    "/imageserver/plumtree/portal/*" - 
&nbsp;    "/documents/*" {
&nbsp;       set cachetime $::day
&nbsp;    }
&nbsp;    "/portal/server.pt/gateway/*.gif" -
&nbsp;    "/portal/server.pt/gateway/*.css" - 
&nbsp;    "/portal/server.pt/gateway/*.js" -
&nbsp;    "/portal/server.pt/gateway/*.jpg" - 
&nbsp;    "/portal/server.pt/gateway/*.png" {
&nbsp;       set cachetime $::workday
&nbsp;    }
&nbsp;    "*.gif" -
&nbsp;    "*.jpg" -
&nbsp;    "*.png" {
&nbsp;       set cachetime $::workday
&nbsp;    }
&nbsp;    "*.css" - 
&nbsp;    "*.js" { 
&nbsp;       set cachetime $::workday
&nbsp;    }
&nbsp;    default { 
&nbsp;       set cachetime 0
&nbsp;    }
&nbsp;  }
&nbsp;  if {not($cachetime == 0)} {
&nbsp;      HTTP::header remove "If-None-Match"
&nbsp;  }
&nbsp; 
&nbsp;  log local0. "URI is [HTTP::path], Cache time: $cachetime"
&nbsp;}&nbsp;&nbsp;

harold_deadman_ · Answer

This is the rest of the i-rule that is actually telling the browser to cache stuff. We are removing the Etag because it isn't adding any value over last-modified date and our two IIS servers are returning different Etag values for the same file (because their config's aren't in sync). &nbsp;
&nbsp;Internet Explorer doesn't seem to want to cache anything with a Vary header in it. We haven't tried stripping that out yet, not sure if we can since I think it is being added by the HTTP profile because we have caching and compression on. I don't want the Vary header because we are already telling proxies that the content is private so intermediary caches won't cache it. &nbsp;&nbsp;
&nbsp;when HTTP_RESPONSE priority 900 {
&nbsp;    if { (not([HTTP::header exists "Cache-control"])) and (not([HTTP::header exists "Content-Disposition"])) } {
&nbsp;        if {not($cachetime == 0)} {
&nbsp;            HTTP::header remove "Etag"
&nbsp;            HTTP::header remove "X-Powered-By"
&nbsp;            HTTP::header insert Cache-Control "private,max-age=$cachetime,post-check=$::postcheck,pre-check=$cachetime,must-revalidate,proxy-revalidate"
&nbsp;            HTTP::header replace Expires [clock format [expr ([clock seconds]+$cachetime)] -gmt true -format "%a, %d %b %Y %T %Z"]
&nbsp;        } else {
&nbsp;            log local0. "Cache time is zero: [HTTP::path]"
&nbsp;        }
&nbsp;    } 
&nbsp;}&nbsp;

spark_86682 · Answer

There's a fascinating post on MSIE 4.x, 5.x, and 6.x behavior with regards to compression, caching, and HTTP headers at http://lists.over.net/pipermail/mod_gzip/2002-December/006826.html (Click here). MSIE 7 is a whole other ball of wax, of course, and I won't claim to know all those corner cases.

matthew_goche_6 · Answer

We have added the following into our iRule:&nbsp;
&nbsp;HTTP::header remove "Vary"&nbsp;
&nbsp;but it seems to still have the Vary header in the response header of files that the browser is not caching.  &nbsp;
&nbsp;I tried to disable the "Vary header" in the profile, but the GUI did not allow since we are using both ramcache and compression.  &nbsp;&nbsp;

bl0ndie_127134 · Answer

Ok lets try a bigger hack then. Can you modify your rule to add a 'Vary" User-Agent' header? I wonder if we can trick IE to look the first instance of the header (you never know).&nbsp;
&nbsp;If you want to pursue this further you might want to open a case with support. I have a feeling that we might have exhausted what we can do here in the forum.

matthew_goche_6 · Answer

We are still having trouble removing the Vary header via an iRule.  I tried deleting it and then reinserting just what I want:  &nbsp;
&nbsp;Vary:  User-Agent&nbsp;
&nbsp;However, it doesn't seem to want to alter the header.  In the meantime, we have removed compression, which in turn, removes the Vary header and the files are now being cached in IE.  &nbsp;
&nbsp;Please let us know if there is any other specific syntac I can use in my iRule to kill the Vary header from these large files.  Thanks!

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Problems encouraging caching on the browser

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