haproxy

# HAProxy HAProxy is the standard for high-performance load balancing. HAProxy 3.0 (2025) adds **Syslog Load Balancing** and improved HTTP/3 QUIC support. ## When to Use - **High Traffic**: Handling millions of requests per second. - **L4 Balancing**: TCP proxying for Database replicas, Redis, or non-HTTP protocols. - **Advanced Logic**: Complex ACLs, rate limiting, and sticky sessions. ## Quick Start ```haproxy frontend http_front bind *:80 default_backend web_servers backend web_servers balance roundrobin server web1 10.0.0.1:80 check server web2 10.0.0.2:80 check ``` ## Core Concepts ### Frontend / Backend Frontend defines how requests enter (ports, certs). Backend defines where they go and how (algorithms, health checks). ### ACLs Access Control Lists. Powerful conditionals. `acl is_api path_beg /api` `use_backend api_servers if is_api` ### Stick Tables In-memory storage for tracking events (e.g. rate limiting by IP). ## Best Practices (2025) **Do**: - **Use Data Plane API**: For dynamic configuration without reloads. - **Enable Prometheus Exporter**: Built-in metrics endpoint. - **Tune `maxconn`**: Critical for preventing resource exhaustion. **Don't**: - **Don't use as Web Server**: It is a proxy. Use Nginx/Caddy for serving static files. ## References - [HAProxy Documentation](https://www.haproxy.org/)