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

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