An Introduction to HAProxy and Load Balancing Concepts


HAProxy, which stands for High Availability Proxy, is a popular open source software TCP/HTTP Load Balancer and proxying solution which can be run on Linux, macOS, and FreeBSD. Its most common use is to improve the performance and reliability of a server environment by distributing the workload across multiple servers (e.g. web, application, database). It is used in many high-profile environments, including: GitHub, Imgur, Instagram, and Twitter.

In this guide, you’ll get a general overview of what HAProxy is, review load-balancing terminology, and examples of how it might be used to improve the performance and reliability of your own server environment.

HAProxy Terminology

There are many terms and concepts that are important when discussing load balancing and proxying. You’ll go over commonly used terms in the following subsections.

Before you get into the basic types of load balancing, you should begin with a review of ACLs, backends, and frontends.

Access Control List (ACL)

In relation to load balancing, ACLs are used to test some condition and perform an action (e.g. select a server, or block a request) based on the test result. Use of ACLs allows flexible network traffic forwarding based on a variety of factors like pattern-matching and the number of connections to a backend, for example.

Example of an ACL:

acl url_blog path_beg /blog

This ACL is matched if the path of a user’s request begins with /blog. This would match a request of, for example.

For a detailed guide on ACL usage, check out the HAProxy Configuration Manual Please visit HAProxy Configuration Manual for more details.