This configuration makes Apache act as an HTTP proxy:

   1  <VirtualHost *:8080>
   2  ProxyRequests On
   3  ProxyVia On
   4  #ProxyRemote * http://...:8080 Uncomment to route requests through another proxy
   5  <Proxy *>
   6  	Order deny,allow
   7  	Deny from all
   8  	Allow from all # Not a good idea, set to allowed IP ranges
   9  </Proxy> 
  10  	
  11  CacheRoot "/tmp"
  12  CacheMaxExpire 24
  13  CacheLastModifiedFactor 0.1
  14  CacheDefaultExpire 1
  15  
  16  ServerName my-proxy
  17  
  18  ErrorLog "/var/log/apache2/proxy-error.log"
  19  CustomLog "/var/log/apache2/proxy-access.log" common
  20  </VirtualHost>

Also read this.

Tips

You can use mod_rewrite to rewrite requests. To rewrite root (/) to /temporary_outage you could use the following rewrite:

   1  RewriteCond %{HTTP_HOST} ^(www\.)?xxx\.com 
   2  RewriteRule /$ http://%{HTTP_HOST}/temporary_outage/ [P,L]