Since we are talking about several thousand of IPs here in at least 1.5k of CIDR ranges, I was looking for the best way to do that that wouldn’t cause a lot of performance impact - the tracking server needs to be fast.

A list of all CIDR ranges with deny turned out to not work thanks to my endpoint definition in nginx using return statements, and those are apparently evaluated before allow and deny statements. But then I got the hint to look at the geo module and with that it was easy to build a map of IP ranges that should be matched and just combining that with an if.

For a first test I created a converter for this list of IP ranges, filtering for the really big players:

#!/bin/bash

URL=https://raw.githubusercontent.com/PodderApps/ipcat/main/datacenters.csv

if [ $1 != "" ]; then
	DATA=$(curl -s $URL | grep -E "$1")
else
	DATA=$(curl -s $URL)
fi


echo 'geo $is_cloud {'
echo '    default 0;'

while IFS= read -r line; do
	start_ip=$(echo $line | cut -d, -f1)
	end_ip=$(echo $line | cut -d, -f2)
	comment=$(echo $line | cut -d, -f3)

	script="import ipaddress; start_ip=ipaddress.IPv4Address(\"$start_ip\"); end_ip=ipaddress.IPv4Address(\"$end_ip\"); print(next(ipaddress.summarize_address_range(start_ip, end_ip)))"
	cidr=$(python3 -c "$script")

	echo "    $cidr 1; # $comment"
done <<< "$DATA"

echo '}'

Calling this like this then created a conf file:

$ sudo ./generate_is_cloud_map "AWS|DigitalOcean|Google" > /etc/nginx/snippets/is-cloud.conf
$ cat /etc/nginx/snippets/ip-cloud.conf
geo $is_cloud {
    default 0;
    3.0.0.0/15; # Amazon AWS
    # ...
}

which I then could use in my nginx location config through an include and an if statement:

include snippets/is-cloud.conf;

# ...

server {
    location /mylocation {
        if ($is_cloud = 1) {
            return 403;
        }
        # ...
    }
}

For now this seems to work. I’m going to give this a day or so and then look into further IP sources and also blocking off the IPv6 ranges.