Sometimes you care about the region or country users come from to present them with a different experience, perhaps due to language or currency for a shop. Let's explore how to do that in a relatively easy few steps.

The setup

You've got some form of linux or bsd running nginx - let's assume it's Debian or Ubuntu.

First Steps

Install the geo-ip tools and update the database.

sudo apt-get update
sudo apt-get install nginx-full geoip-database
curl http://geolite.maxmind.com/download/geoip/database/GeoLiteCity.dat.gz | gunzip > /usr/share/GeoIP/GeoLiteCity.dat

The information is available as many formats: country or even city, however those are respectively long and impossible to list here. Also bare in mind the ip-based geolocation is an approximation that is rough but mostly adequate, you can usually rely on the country information if a user isn't using a proxy, the state and city information can vary especially with mobile networks. Let's just stick to continents here - below are the ones defined in the specification.

Enter nginx

First of all, edit your nginx.conf in /etc/nginx/nginx/ or whereever you keep it, and add the following geoip_city definition as per below under http section.

http {
        # Tell Nginx where we keep our GeoLocation database
        geoip_city /usr/share/GeoIP/GeoLiteCity.dat;
        # all the rest...
        }

Using a very clever nginx directive called map which you can read all about here, we define a variable essentially based on a lookup table (which in this case uses the $geoip_city_continent_code to map the resultant value into $closest_server).

map $geoip_city_continent_code $closest_server {
        default international-waters.mybrand.com;
        AF      africas.mybrand.com;
        AN      penguins.mybrand.com;
        AS      asia.mybrand.com;
        EU      europe.mybrand.com;
        NA      northamericas.mybrand.com;
        OC      oceania.mybrand.com;
        SA      southamericas.mybrand.com;
}

Or to see this visually:

Now that'll give us a value we can use, but what do we do with it? Well there's a few options you could 301/302 (debatable which is more true as it hasn't been redirected either temporarily or permanently but anyway...), or you can use a rewrite rule to internally rewrite the url.

server {
    listen 127.0.0.1:80;
    server_name shop.mybrand.com;

    rewrite ^ $scheme://$closest_server$request_uri break;
}

server {
    listen 127.0.0.1:80;
    server_name africas.mybrand.com penguins.mybrand.com asia.mybrand.com europe.mybrand.com northamericas.mybrand.com oceania.mybrand.com southamericas.mybrand.com;
    root /srv/shop.mybrand.com/html;
    index index.html;
}

Conclusion

It's actually surprisingly simple to do this, and takes the heavy-lifting out of your code, which is a huge benefit for portability, and allows a much more flexible setup. This is just the tip of the iceberg as their are other parameters available such as country, state and region (as discussed). A word to the wise, if you're wanting to do this for language reasons, try using the user's locale (it'll be much more accurate and specific).