How to Configure Apache Load Balancer

Last updated on August 10th, 2020 at 03:05 am

Apache load balancer helps your websites handle large traffic loads without any performance issues. Here’s how to configure Apache Load balancer for your website.

Table of Contents

Apache Load Balancer Configuration

Here are the steps to configure Apache load balancer for your website, on Ubuntu/Debian systems.

1. Install Required Apache modules

We require 4 Apache modules to configure Apache load balancer – mod_proxy, mod_proxy_http, mod_proxy_balancer, mod_lbmethod_byrequests

mod_proxy is the main proxy module that redirects requests and allows Apache to act as gateway to backend servers
mod_proxy_http allows support for proxying HTTP requests
mod_proxy_balancer and mod_lbmethod_byrequests add load balancing capabilities to Apache web server.

Open terminal and run the following commands to install pre-requisite Apache modules.

$ sudo a2enmod proxy
$ sudo a2enmod proxy_http
$ sudo a2enmod proxy_balancer
$ sudo a2enmod lbmethod_byrequests

Bonus Read : Apache Reverse Proxy Configuration

2. Restart Apache Server

Restart Apache Server to apply changes

$ sudo service apache2 restart

3. Setup backend servers

To configure Apache Load Balancer, we will install flask & setup 2 servers to run on port 8080 and port 8081 as a backend server.

$ sudo apt-get update
$ sudo apt-get -y install python3-pip
$ sudo pip3 install flask

Flask comes with a readymade ~/backend.py file that returns “Hello World” on requesting home page.

from flask import Flask
app = Flask(__name__)

@app.route('/')
def home():
    return 'Hello world!'

Bonus Read : How to Install and Configure mod_pagespeed

We will create a copy of it for our second server.

$ sudo cp ~/backend.py ~/backend1.py

Open backend1.py and change the “Hello World” message in last line to “Hello World 2”

from flask import Flask
app = Flask(__name__)

@app.route('/')
def home():
    return 'Hello world 2!'

Bonus Read : How to Check if mod_expires is enabled

We will run the first flask server

$ FLASK_APP=~/backend.py flask run --port=8080 >/dev/null 2>&1 &

You can test this server by running curl command

$ curl http://127.0.0.1:8080/

You will see the output as Hello World!

We will run the second flask server

$ FLASK_APP=~/backend1.py flask run --port=8081 >/dev/null 2>&1 &

You can test this server by running curl command

$ curl http://127.0.0.1:8081/

You will see the output as Hello World 2!

Now we have 2 backend servers ready to handle the load. We will be distributing load between these 2 servers.

Bonus Read : How to Secure Apache with Let’s Encrypt on Debian 10

4. Configure Apache Load Balancer

We need to modify Apache’s default configuration file to configure Apache load balancer. Open Apache configuration in text editor

$ sudo vi /etc/apache2/sites-available/000-default.conf

Add the following lines to VirtualHost tag in Apache configuration file.

     <Proxy balancer://mycluster>
       BalancerMember http://127.0.0.1:8080
       BalancerMember http://127.0.0.1:8081
      </Proxy>
      ProxyPreserveHost On
      ProxyPass / balancer://mycluster/
      ProxyPassReverse / balancer://mycluster/

Let’s look at the 3 directives.

ProxyPreserveHost causes Apache to preserve original host header and pass it to back-end servers.
ProxyPass is the main proxy directive which states that everything under root (/) should be directed to back-end cluster ( we have named it mycluster) of servers. If Apache gets request for /example, then it will send the request to http://your_backend_server/example
ProxyPassReverse tells Apache to modify response header in the response received from back-end server. This is useful in case the back-end server returns a location redirect response, then the client will be redirected to Apache proxy server, instead of back-end server.
We list our backend servers in Proxy tag named balancer://mycluster . You can change it to anything else. Inside this proxy tag, we list each backend server as BalancerMember. So your cluster’s Proxy tag can have one or more BalancerMember

<VirtualHost *:80>
...
   <Proxy balancer://mycluster>
      BalancerMember http://127.0.0.1:8080
      BalancerMember http://127.0.0.1:8081
    </Proxy>
    ProxyPreserveHost On
    ProxyPass / balancer://mycluster/
    ProxyPassReverse / balancer://mycluster/
... 
</VirtualHost>

Bonus Read : How to Enable mod_headers in Apache