I want to have one server with HAproxy and a standalone mod_security installed which routes every packets to mod_security first and check by its rules.
Then if there wasn’t anything suspicious in packets (SQL Injection, DOS Attacks, …) pass them back from mod_security to haproxy and haproxy routes them to multiple servers with different webservers.
Therefore I don’t need to install and config mod_security on all my webservers.
2
Answers
This is technically possible, possibly with running 2 instances of HAProxy. However, you will need a webserver to run underneath ModSec, typically Apache or nginx, and this kind of negates the advantage of not having to install ModSec on all your webservers.
The standard setup is: haproxy -> reverse-proxies with ModSec -> application-servers
Just to answer this old, but still valid, question:
The solution should be to use HAProxies Stream Processing Offload Engine (SPOE) through the Stream Processing Offload Protocol (SPOP) to talk a Stream Processing Offload Agent (SPOA) which is a standalone modsecurity daemon.
HAProxy example config from their github repo
There’s also a Github project where the daemon has been made available as Docker container
Offical HAProxy blog post