The History of HAProxy

For over 20 years, HAProxy has been one of the industry’s most successful open source projects. It’s been continuously tested and improved by a massive and active open source community. See how HAProxy evolved into an essential part of the world’s technology infrastructure.



  • Testing tool developed to gauge how an application would perform when facing lots of clients with 28 Kbps modems



  • Modified to include regex-based header rewriting, with a minimalistic config language.

  • Keywords introduced: listen, server


HAProxy 1.0

  • Developed to offload traffic from hardware load balancers


HAProxy 1.1

  • Simple round-robin scheduler

  • Simple health checks

  • Improved its logging capabilities

  • Cookie insertion


HAProxy 1.2

  • IPv6 support on the client side

  • Replaced the wait-queue linked list with a rbtree

  • Introduced maxconn setting

  • Keywords introduced: except, forwardfor


HAProxy 1.3

  • Elastic Binary Trees within the internal scheduler

  • TCP scripting

  • Explicit source port ranges

  • Interface binding


HAProxy 1.4

  • RDP protocol support with server stickiness and user filtering

  • Client-side Keep-Alive

  • HTTP authentication support

  • ACL-based persistence


HAProxy 1.5

  • SSL and compression

  • Data sampling

  • Server-side Keep-alive

  • DDoS protection


HAProxy 1.6

  • Lua Scripting

  • Server-side connection multiplexing

  • Dynamic buffer allocation

  • Replaced Zlib with an in-house stateless implementation


HAProxy 1.7

  • HAProxy Runtime API

  • Server hot reconfiguration

  • SPOE (Stream Processing Offload Engine)

  • Introduced content processing agents & multi-type certs


HAProxy 1.8

  • Improved HAProxy Runtime API

  • Introduced multithreading

  • Dynamic Cookies

  • New MUX layer


HAProxy 1.9

  • HTX – internal HTTP representation

  • End-to-End HTTP/2 (enabling gRPC)

  • Improved queue priority control

  • Improved the scalability of the multithreading feature


HAProxy 2.0

  • Cloud-native theading and logging

  • HAProxy Kubernetes Ingress Controller

  • HAProxy Data Plane API

  • Prometheus exporter

HAProxy 2.1

  • Dynamic SSL Certificate Updates

  • FastCGI

  • Improved debugging

  • Native Protocol Tracing


HAProxy 2.2

  • Fully Dynamic SSL Certificate Storage

  • Improved idle connection management

  • Native Response Generator

  • Health Check System Overhaul

HAProxy 2.3

  • Syslog Protocol (UDP/TCP)

  • OpenTracing (SPOE)

  • SSL/TLS Environments

  • Improved Cache


HAProxy 2.4

  • HTTP/2 WebsocketsFIX & MQTT Protocols

  • Dynamic SSL Certificate Storage

  • Built-in OpenTracing

  • DNS TCP Resolution

Today, HAProxy is the world’s fastest and most widely used software load balancer. It’s responsible for providing high availability, security, and observability to some of the world’s highest-trafficked websites. Explore our User Spotlight Series to learn how the world’s top architects and engineers chose to implement HAProxy within their application architectures.

User Spotlight Series