GEOCDN

This project is used too keep track of the nginx configuration used on GARR MIRRORS, see http://mirror.garr.it.

Objective of this configuration is being able to redirect requests for selected URI to a proxy cache. We also want to be able to redirect based on ASnum.

To use it include geocdn.conf in the http stanza of nginx configuration

http {

include  /etc/nginx/geocdn/geocdn.conf;

}

GeoIP localization

The nginx geoip module is used to determine country and also ASnum. We account for reverse proxies (varnish cache):

geoip_org     /etc/nginx/geocdn/GeoIPASNumv6.dat;
geoip_country /etc/nginx/geocdn/GeoIPv6.dat;
geoip_proxy   193.206.139.32/28;
geoip_proxy   193.206.140.32/28;

Now we only want the number of the AS not the entire description so just use a map with regexp substituion:

map $geoip_org $my_geoip_org  {
  ~^(?P<ascode>AS[0-9]+)\ .*$  $ascode;
}

$my_geoip_org now contains for instance AS137 for GARR autonomous system.

Mapping AS num to CDN site

The following map enables us to map ASes to cdn sites, again with a map:

map $my_geoip_org $cdn_site {
  default     cdn;
  include     /etc/nginx/geocdn/as-to-site.conf;
}

Where as-to-site.conf contains

AS137    cdnmi;
AS3269   cdnrm;

Note that $cdn_site will be used to redirect to $cdn_site.mirror.garr.it.

Actual redirection

Redirection should happen only for defined request URIs and only if the request comes from a client, not a CDN cache. So we define a variable to distinguish clients from caches:

geo $frontend {
  default C;
  193.206.139.32/28 P;
  193.206.140.32/28 P;
}

We only have to decide which URLs should be redirected to the CDN:

map $request_uri $uri_for_redirection {
        default $request_uri;
        include /etc/nginx/geocdn/redirections.conf;
}

redirections.conf maps every URL that should be redirected to the string OK

Redirections happen in a server {…} block

set $redirect_to_cdn "$frontend$uri_for_redirection";
if ($redirect_to_cdn ~ "^COK" ) {
  rewrite ^ http://$cdn_site.mirror.garr.it/mirror2$request_uri
  break;
}

In our example request coming from a client for /mirrors/test/ will be mapped to $cdn_site.mirror.garr.it/mirror2/mirrors/test.