Sometimes you need to have a rough idea of where your website visitor is located. There’s many ways to geolocate them, but if you just want to go to country level then MaxMind have free geo databases available to help you. When we needed to do this quickly on-the-fly at EmberAds, we came up with the trifle gem, which supports ipv4 and ipv6 lookups.

Recently I was searching for something else to do with nginx and ran across a mailing list thread about using the maxmind database with nginx’s HTTP Geo module and do the lookup directly in nginx itself. Finally got a chance to sit down and work out the logistics of doing this. I’ve done this on an ubuntu 12.04 box, with the expected config file layouts that come with ubuntu.

Run the following on your server (as someone with write access to nginx config files):

# Generate the text file for nginx to import
perl <(curl -s https://raw.github.com/nginx/nginx/master/contrib/geo2nginx.pl) \
< <(zip=$(tempfile) && \
curl -so $zip http://geolite.maxmind.com/download/geoip/database/GeoIPCountryCSV.zip \
&& unzip -p $zip) > /etc/nginx/nginx_ip_country.txt

# Tell nginx to work out the IP country and store in variable
echo 'geo $IP_COUNTRY {
  default --;
  include /etc/nginx/nginx_ip_country.txt;
}' > /etc/nginx/conf.d/ip_country.conf

Now go find the http block for the vhost you want to have the header passed to, and assuming it’s passenger, add the following:

passenger_set_cgi_param HTTP_X_IP_COUNTRY $IP_COUNTRY;

(If you don’t use passenger, look at the docs for proxy_pass_header or fastcgi_pass_header to see which you’ll require for your setup.)

Reload nginx, and behold, request.env["HTTP_X_IP_COUNTRY"] (assuming a rack app running under ruby) will be a two letter country code, or "--".

Unfortunately this is IPv4 only currently, there’s a thread on the nginx mailing list from November 2012 saying IPv6 support should be coming on the v1.3 branch of nginx, but with no known ETA. So currently for IPv6 support, take a look at EmberAds’ trifle gem instead.