Source IP based reverse proxy

If you want to proxy some source IP ranges/subnets to one server and onther subnets to go to a different server, you can do this using mod_rewrite for proxying. You will have to setup a rewrite condition based on the source IP and a rewrite rule with the [P] flag. Something like this should work:

RewriteCond %{REMOTE_ADDR} ^10\.2\.
RewriteRule ^/(.*) http://old-app/$1 [P]
ProxyPassReverse / http://serverA/

RewriteCond %{REMOTE_ADDR} ^10\.3\.
RewriteRule ^/(.*) http://new-app/$1 [P]
ProxyPassReverse / http://serverB/

One possible scenario for this if you want to migrate your users from server A to server B but you want to migrate one IP range at the time.

If you're using Apache 2.4 or newer you can also achieve this with the following configuration:

<If "-R '10.2.0.0/16'">
  ProxyPassReverse / /http://serverA/
</If>
<ElseIf "-R '10.3.0.0/16'">
  ProxyPassReverse / /http://serverB/
</ElseIf>
<Else>
  ProxyPassReverse / /http://serverC/
</Else>