Implementing a Dynamic IP Blacklist with Nginx, Lua, and Redis

To prevent malicious crawlers or abusive users from accessing a server, a dynamic IP blacklist is required that rejects requests from IPs listed in the blacklist.

There are several ways to implement an IP blacklist: configuring iptables at the OS level, using Nginx's deny directive or Lua plugins, or checking the client IP in the application layer. This article adopts the Nginx + Lua + Redis architecture to create a Web Application Firewall (WAF) that dynamically blocks frequent IPs.

Install LuaJIT :

[root@hd03 ~]# tar -xf LuaJIT-2.0.5.tar.gz -C /opt/

[root@hd03 ~]# cd /opt/LuaJIT-2.0.5/

[root@hd03 LuaJIT-2.0.5]# make && make install

Set environment variables:

export LUAJIT_LIB=/usr/local/lib

export LUAJIT_INC=/usr/local/include/luajit-2.0

Source the profile and create a symlink for the shared library.

[root@hd03 LuaJIT-2.0.5]# source ~/.bash_profile

[root@hd03 LuaJIT-2.0.5]# ln -s /usr/local/lib/libluajit-5.1.so.2 /lib64/libluajit-5.1.so.2

Compile Nginx with required modules (including Lua and Redis support):

[root@hd03 ~]# tar -xf nginx-1.20.2.tar.gz -C /opt/

[root@hd03 nginx-1.20.2]# ./configure --user=nginx --group=nginx --prefix=/usr/local/nginx --sbin-path=/usr/local/nginx/bin/nginx --conf-path=/usr/local/nginx/conf/nginx.conf --pid-path=/usr/local/nginx/logs/nginx.pid --lock-path=/usr/local/nginx/run/nginx.lock --error-log-path=/usr/local/nginx/logs/error.log --http-log-path=/usr/local/nginx/logs/access.log --http-client-body-temp-path=/var/cache/client_temp --http-proxy-temp-path=/var/cache/proxy_temp --http-fastcgi-temp-path=/var/cache/fastcgi_temp --http-uwsgi-temp-path=/var/cache/uwsgi_temp --http-scgi-temp-path=/var/cache/scgi_temp --with-http_v2_module --with-http_ssl_module --with-http_realip_module --with-http_addition_module --with-http_sub_module --with-http_dav_module --with-http_flv_module --with-http_mp4_module --with-http_gunzip_module --with-http_gzip_static_module --with-http_random_index_module --with-http_secure_link_module --with-http_stub_status_module --with-http_auth_request_module --with-mail --with-mail_ssl_module --with-file-aio --with-threads --with-stream --with-stream_ssl_module --without-mail_pop3_module --without-mail_imap_module --without-mail_smtp_module --add-module=/usr/local/ngx_devel_kit-0.3.0 --add-module=/usr/local/lua-nginx-module-0.10.13

[root@hd03 nginx-1.20.2]# make && make install

[root@hd03 nginx-1.20.2]# ln -s /usr/local/nginx/bin/nginx /usr/bin/

Start Nginx: [root@hd03 nginx-1.20.2]# nginx Deploy the WAF components :

Install lua-resty-redis module:

[root@hd03 ~]# cd /usr/local/lua-resty-redis

[root@hd03 lua-resty-redis]# make && make install

Install and configure Redis : [root@hd03 ~]# yum install redis -y Modify /etc/redis.conf (example settings):

bind 0.0.0.0

daemonize yes

logfile /var/log/redis/redis.log

requirepass 123456

dir /data/redis

Update Nginx configuration to use the WAF :

lua_shared_dict limit 8m;

lua_package_path "lua;/usr/local/nginx/conf/waf/redis.lua;;";

Create access_limit.lua (the script checks request frequency, stores counters in Redis, and adds offending IPs to the blacklist).

Place the script in /usr/local/nginx/conf/waf and test the configuration: [root@hd03 waf]# nginx -t Result:

nginx: the configuration file /usr/local/nginx/conf/nginx.conf syntax is ok

nginx: configuration file /usr/local/nginx/conf/nginx.conf test is successful

Reload Nginx: [root@hd03 waf]# nginx -s reload When a client refreshes the site more than 10 times within one minute, the IP is cached in Redis and automatically blocked for 5 minutes, returning a 403 status code.

Verify in Redis:

Check request count:

redis-cli -h 192.167.16.8 -a 123456

get USER-COUNT-192.167.16.8

→ "9" (means 9 hits cached).

Retrieve blacklist set: smembers limit:ip:blacklist → "192.167.16.8".

Manually add an IP to the blacklist: sadd limit:ip:blacklist 192.167.16.8 This completes the end‑to‑end setup of a dynamic IP blacklist using Nginx, Lua, and Redis.