Apache cookie-based transparent proxy / redirect - apache

Question

I have a number of sites running on the same machine, served by httpd. Each of the sites is set up as a VirtualHost on a different subdomain. Furthermore, for each subdomain, there are two VirtualHosts on different ports: one for the 'stable' version, one for the 'beta' version. The stable version is hosted on port 80.
Upon logging into the (stable version of the) sites, a cookie is set if the backend determines the user should be using the beta version.
I'd like Apache to detect this cookie on subsequent requests to the stable version and (without the user being aware) redirect the request to the beta version.
How can I achieve this?
I've tried using RewriteCond / RewriteRule in httpd.conf, but it doesn't seem to have any effect - perhaps Apache ignoring it in favour of the matching VirtualHost, or is sensitive to ordering (I think the VirthalHost definitions are being included first)? Perhaps I should be using mod_proxy, anyway?
Config
I've included (anonymised) snippets of my config below
httpd.conf
Listen 80
NameVirtualHost *:80
Listen 81
NameVirtualHost *:81
Include "/path/to/checkout/config/[stage]/apache2/*.conf" # VirtualHosts of sites
Include "/path/to/checkout/config/common/apache2/*.conf" # My attempted redirect
config/[stage]/apache2/[site]/apache2/[app-stable].conf
<VirtualHost *:80>
ServerName [app.hostname]
ServerAlias [alternative-app-name.hostname]
DocumentRoot "/var/www-application/release-base/current/app/public"
<Directory "/var/www-application/release-base/current/app/public/">
Options Indexes FollowSymLinks
AllowOverride All
</Directory>
<!-- snip -->
</VirtualHost>
config/[stage]/apache2/[site]/apache2/[app-beta].conf
<VirtualHost *:81>
ServerName [app.hostname]
ServerAlias [alternative-app-name.hostname]
DocumentRoot "/var/www-application/beta-release-base/current/app/public"
<Directory "/var/www-application/beta-release-base/current/app/public/">
Options Indexes FollowSymLinks
AllowOverride All
</Directory>
<!-- snip -->
</VirtualHost>
config/common/apache2/common.conf
# !!! This has no effect !!!
RewriteEngine On
RewriteCond %{HTTP_COOKIE} cookiename
RewriteCond %{SERVER_PORT} !8081
RewriteRule ^ https://%{HTTP_HOST}:8081%{REQUEST_URI} [R,L] # (R for debugging)
App .htaccess (in case it's relevant)
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} -s [OR]
RewriteCond %{REQUEST_FILENAME} -l [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^.*$ - [NC,L]
RewriteRule ^.*$ index.php [NC,L]

Answer 1

You have two problems:
The redirects in global scope are ignored; move them to vhost scope
The "%{HTTP_HOST}" var includes the port number, so you are redirecting to http://hostname:80:81/foo (hence your "hang")
In order to make this transparent, you need to use the [P] flag on the RewriteRule, and include a ProxyPassReverse directive. Your final directives (in each 'stable' conf file) should be as follows:
RewriteCond %{HTTP_COOKIE} absVersion
RewriteRule ^/(.*) http://hostname:81/$1 [P]
ProxyPassReverse / http://hostname:81/
Note that this requires mod_proxy (and any necessary submodules, e.g. mod_proxy_http) to be enabled.