Integrate Fail2ban with Cloudflare API (V4) to mitigate HTTP flooding attacks using Nginx and Roboo.

Requirements:

1. Nginx
2. Roboo (https://github.com/yuri-gushin/Roboo)
3. Fail2ban
4. A Cloudflare account (https://www.cloudflare.com/a/sign-up)
5. Ruby 1.9.3 or later

1. Signup to Cloudflare: https://www.cloudflare.com/a/sign-up

2. Go to https://www.cloudflare.com/a/account/my-account and select View API Key.

3. Setup your site(s) to use Cloudflare

1. Install Fail2ban on the server running Nginx and Roboo.

2. Add the nginx-roboo.conf file to your filter.d dir.

3. Add the cloudflare.conf file to your action.d dir.

4. Edit the cloudflare_api_manager.rb file and set your CLOUDFLARE_USERNAME and CLOUDFLARE_API_KEY (line 8 and 9).

5. Optional add any proxy information if you need to access Cloudflare via a proxy server (line 15 to 18).

6. Add the following to your jail.conf file:

   [nginx-roboo]
   enabled   = true
   port      = all
   filter    = nginx-roboo
   banaction = cloudflare
   logpath   = /var/log/nginx/challenged.log
   maxretry  = 250
   

7. Add the cloudflare_api_manager.rb script to a location accessible to the fail2ban user and set appropriate permissions. Remember that your Cloudflare API keys are stored in this script so handle with care!

8. Verify that an IP is added to your Cloudflare firewall by banning an IP:

   /path/to/ruby /path/to/cloudflare_api_manager.rb ban 1.2.3.4
   

9. Verify that the IP is removed from your Cloudflare firewall by unbanning the IP:

   /path/to/ruby /path/to/cloudflare_api_manager.rb unban 1.2.3.4
   

10. Restart Fail2ban

This will make Fail2ban monitor the file /var/log/nginx/challenged.log and each client with more than 250 challenge attempts will be banned using the cloudflare filter.

Bad clients will automatically be banned (presented with a Google reCAPTCHA challenge) at Cloudflare instead of continuously hitting your server. After the defined bantime clients are automatically removed from the blacklist again.

It might be a good idea to whitelist the IP range of Cloudflare in Fail2ban using the ignoreip section. A current list of the IP ranges of Cloudflare can be found here: https://www.cloudflare.com/ips/

NOTE: At the moment Fail2ban doesn't work with IPv6 so it might be a good idea to disable IPv6 support in the Cloudflare admin interface for each site you want to protect using Fail2ban.