[Discuss] Active Health check in Nginx

This is to support active health checks in nginx.
The open-source nginx does not support the active health check feature, but there are some modules enabling it.
- https://github.com/yaoweibin/nginx_upstream_check_module
- https://github.com/lyokha/nginx-healthcheck-plugin

These modules require compiling of Nginx source code.
It means we need to keep codes to build Nginx including a health check module.

Without the active health check, it's not simple to implement a zero downtime deployment feature.
Without it, we have to exclude a target controller from all Nginx before deploying it which is simple to implement with Ansible.
But I am unsure if it is worth having Nginx codes in the core repo to support active health check.