what does this configuration in apache mean?

apache http http-headers vary
omg picture omg · Jun 9, 2009 · Viewed 11.4k times · Source 
Header append Vary User-Agent env=!dont-vary

Can anyone give a detailed explanation for this?

Answer

Paul Dixon picture Paul Dixon · Jun 9, 2009

This uses Apache mod_headers to append the value "User-Agent" to the Vary HTTP header, but only if the dont-vary environment is not set.

But what is the Vary header? See RFC2616 which says

The Vary field value indicates the set of request-header fields that fully determines, while the response is fresh, whether a cache is permitted to use the response to reply to a subsequent request without revalidation

If you deliver different HTML markup depending on the User-Agent header, you might use a Vary header with User-Agent in it to ensure that a caching proxy didn't serve content intended for browser X to browser Y.

Related questions

416 Requested Range Not Satisfiable

Context: I am using a software package called Social Engine. It is extremely buggy. Anyway, I asked (paid even) the Social Engine people to do an upgrade and when they finally did so, I logged into the site and noticed …

Read More
Https to http redirect using htaccess

I'm trying to redirect https://www.example.com to http://www.example.com. I tried the following code in the .htaccess file RewriteEngine On RewriteCond %{HTTP_HOST} ^example\.com$ [NC] RewriteRule ^(.*)$ http://www.example.com/$1 [R=301,L] This code successfully …

Read More
Redirect HTTP to HTTPS on default virtual host without ServerName

On my apache server I'd like to be able to redirect all incoming http requests to the equivalent https request. The catch is that I'd like to be able to do this for my default virtual host without specifying the …

Read More