Master HAProxy: Configure ACLs, Backends, Frontends, and Stats in Minutes

HAProxy (High Availability Proxy) is a free, fast, and reliable load‑balancing and proxy solution written in C for TCP/HTTP‑based applications.

Basic Concepts

The main components of an HAProxy configuration are Access Control Lists (ACLs), backends, and frontends.

ACL

An ACL is a test expression that decides actions based on the result of the test, such as selecting a server and forwarding a request.

Syntax:

acl <aclname> <criterion> [flags] [operator] [<value>] ...

Example:

acl acl_myApp path_sub myApp

Backend

A backend is a group of servers that actually process forwarded requests. It includes a load‑balancing algorithm and a list of servers with ports.

Basic syntax:

backend <backendname>
balance <loadbalancing algorithm>
server <name> <ip>:<port> check
...

Example:

backend myAppBackend
balance roundrobin
server myAppServer1 172.21.28.1:8080 check
server myAppServer2 172.21.28.2:8080 check

Frontend

The frontend defines how requests are forwarded to a backend. It consists of IP addresses, a port, ACLs, and use_backend rules.

Syntax:

frontend <frontend name>
bind <IPs or wildcard>:80
acl <aclname> <criterion> [flags] [operator] [<value>] ...
use_backend <backend name> if <aclname>

Example:

frontend myAppFrontEnd
bind *:80
acl acl_myApp path_sub myApp
use_backend myAppBackend if acl_myApp

Statistics (Optional)

HAProxy can expose a statistics page showing server status, connection counts, etc. Enable it by adding a listen stats section:

listen stats
bind *:9999
stats enable
stats hide-version
stats uri /stats
stats auth admin:admin@123

Complete Configuration Example (haproxy.cfg)

#HA Proxy Config
global
daemon
maxconn 256
defaults
mode http
timeout connect 5000ms
timeout client 50000ms
timeout server 50000ms
listen stats
  bind *:9999
  stats enable
  stats hide-version
  stats uri /stats
  stats auth admin:admin@123
frontend myApp
  bind *:80
  acl acl_myApp path_sub myApp
  use_backend myAppBackEnd if acl_myApp
backend myAppBackEnd
  balance roundrobin
  server myAppServer1 127.0.0.1:8081 check
  server myAppServer2 127.0.0.1:8082 check

Deploy HAProxy on Linux

Download the source code from the HAProxy website.

Extract it: tar xvzf haproxy-1.8-dev1.tar.gz Compile: cd haproxy-1.8-dev1 && make TARGET=linux2628 Create haproxy.cfg with the configuration above.

Start HAProxy: ./haproxy -f haproxy.cfg Access the stats page at http://localhost:9999/stats.

When accessed, the stats page displays the status interface as shown in the image below.