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From Justin Ruthenbeck <>
Subject Re: [OT] Webapp upgrades and browser caching
Date Thu, 07 Oct 2004 18:53:44 GMT


Thanks for your comments.

By adding the <META> expires tag, it sounds like you setting the system 
up to schedule the upgrade.  By this, I mean that you know you're gonna 
upgrade a week from today, so you configure Apache to suggest that all 
content should expire at that time.  Sounds reasonable.

In our situation, we have our webapps installed offsite in clients' 
facilities, so all/most of the upgrade process needs to be fool-proof... 
reconfiguring Apache 1 week (or whatever) before the upgrade isn't really 
an option.  Aside from this, any more idea about how to handle this?


>For static web pages you can use a tag like this:
>If the browsers still have a problem you might be able to configure 
>Apache to output a header will all content called EXPIRES.  I think you 
>can if I remember right from some docs I read.  You will have to look at 
>Apache for that.  I'm not sure about tomcat being able to handle that or 
>not, but the apache bit should prepend the header I believe.  The only 
>other way would be to output all images and static pages from a servlet 
>of some kind and add the header yourself to the request.  Browsers 
>should honor that tag or header for all images down the line from your 
>html or jsp pages, but may not.
>Some browsers may be able to be set to ignore this all together 
>though.  Sometimes it is even worse than that.  I have seen ISP's who 
>think they are slick who install a cache in their systems, and they 
>basically become a proxy for the users.  If they are ignoring such 
>things your users would have to contact them.  I have seen some who do 
>this for different protocols even http and https differently.  That one 
>irked me pretty good.
>Anyways, I use expires in all my jsp and html files.  I haven't ever 
>tried the other stuff for the headers from Apache, but think I remember 
>reading about it in the Apache docs.  I have output that header from 
>servlets and ISAPI dlls before.
>Someone else may be able to offer more help.

At 11:21 AM 10/7/2004, you wrote:
>Justin Ruthenbeck wrote:
>>I'm looking for some advice about how to handle the following situation.
>>(1) Apache 2.x in front of Tomcat 5.x
>>(2) Deploy new web application.  Bunch of servlets, bunch of jsps, 
>>bunch of static content (mainly js, css).
>>(3) Many users use the application, during which time their browsers 
>>cache lots of static content
>>(4) We do a major version upgrade of the webapp, including (almost) all 
>>new static content, but URLs stay the same (to alleviate 
>>bookmark-maintenance requirements).
>>The problem arises when the browsers continue to use their cached 
>>version of the static content.  Now, the browsers eventually get 
>>updated, but immediately after deployment there are huge numbers of 
>>graphical and functional (js files) problems.  It seems like behavior 
>>in this area is widely different amongst browsers and/or their settings.
>>I have only come up with the following option:
>>(1) Play with URLs.  New deployments can be deployed under
>>     a different url domain like:
>>     This would force browsers to get new content since the
>>     content appears as totally new content to the browser.
>>Aside from disabling static content caching, are there any other 
>>options out there?
>>Much thanks for the help!

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