Use Nginx to server different pages depending on IP address/subnet

For reasons to hideous to go into... I'm using Nginx as a webserver and would like it to serve one page for internal users (say on 10.0.0.0/16) and another page to external users on any other IP address.

For example:

• "Internal" PC with an IP of 10.0.0.34 goes to company.com/page.html gets page internal.html

• "External" PC with an IP of 8.8.8.8 goes to company.com/page.html gets page external.html

Make use of Nginx geo module. It lets you set variable's value based on a client IP address. geo directive must be in http section:

http {
  geo $client {
    default extra;
    10.0.0.0/8 intra;
  }

You can use it later in locations to lookup files

location / {
  try_files $uri.$client $uri = 404;
}

Which means, Nginx will set $client to either extra or intra based on a client's IP. Let's assume it's a Intranet client. If a client asks for page.html, Nginx will search for file /your/root/page.html.intra. If there is no such file, it will search for /your/root/page.html. If it cannot find neither of these, Nginx returns 404 "Not Found" response. More on "try_files" in the documentation

By the way, index directive supports variables as well. E.g.

index index.$client.html index.html;