Load balancing refers to efficiently distributing incoming network traffic across a group of backend servers, also known as a server farm or server pool. Load Balancing improves the distribution of workloads across multiple computing resources. Using multiple components with load balancing instead of a single component may increase reliability and availability through redundancy.
Load Balancer is the device that perform Load Balancing. Hardware and software load balancers may have a variety of special features. The fundamental feature of a load balancer is to be able to distribute incoming requests over a number of backend servers in the cluster according to a scheduling algorithm.
In this post, we will configure a HTTP Load Balancer with HAProxy to distribute HTTP workload between two webservers.
This Article Provides:
System Specification:
We have two Apache Web Servers webserver-01.example.com and webserver-02.example.com and we want to configure a HTTP Load Balancer for them i.e. haproxy-01.example.com.
| Hostname | haproxy-01.example.com | webserver-01.example.com | webserver-02.example.com |
| IP Address | 192.168.116.30/24 | 192.168.116.31/24 | 192.168.116.32/24 |
| Operating System | CentOS 7 | CentOS 7 | CentOS 7 |
| Web Server | NA | Nginx | Nginx |
Configure HAProxy on CentOS 7:
To ensure that our webservers are properly configured and browsable, open their URLs in a Browser.
I have set different index pages on both servers, to differentiate between servers, when we are accessing using the load balancer.
Connect to the haproxy-01.example.com and install HAProxy.
[root@haproxy-01 ~]# yum install -y haproxy
Loaded plugins: langpacks, product-id, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
Resolving Dependencies
--> Running transaction check
---> Package haproxy.x86_64 0:1.5-0.3.dev22.el7 will be installed
--> Finished Dependency Resolution
Dependencies Resolved
================================================================================
Package Arch Version Repository Size
================================================================================
Installing:
haproxy x86_64 1.5-0.3.dev22.el7 localyum 696 k
Transaction Summary
================================================================================
Install 1 Package
Total download size: 696 k
Installed size: 2.2 M
Downloading packages:
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Installing : haproxy-1.5-0.3.dev22.el7.x86_64 1/1
Verifying : haproxy-1.5-0.3.dev22.el7.x86_64 1/1
Installed:
haproxy.x86_64 0:1.5-0.3.dev22.el7
Complete!
HAProxy has been installed.
Now configure rsyslog to handle HAProxy logs.
[root@haproxy-01 ~]# vi /etc/rsyslog.conf
Search and uncomment following lines.
$ModLoad imudp
$UDPServerRun 514
Add following directive in the same file.
# HAProxy Logging
local2.* /var/log/haproxy.log
Save settings and exit.
Restart rsyslog service to apply changes.
[root@haproxy-01 ~]# systemctl restart rsyslog.service
Now configure HAProxy settings according to our environment.
[root@haproxy-01 ~]# vi /etc/haproxy/haproxy.cfg
Add following directives in this file.
# HAProxy Load Balancer for Apache Web Server
frontend http-balancer
bind 192.168.116.30:80
default_backend web-servers
backend web-servers
mode http
balance roundrobin
stats enable
stats auth admin:123
server webserver-01 192.168.116.31:80 check
server webserver-02 192.168.116.32:80 check
Save settings and exit.
Start and enable haproxy service.
[root@haproxy-01 ~]# systemctl start haproxy ; systemctl enable haproxy
ln -s '/usr/lib/systemd/system/haproxy.service' '/etc/systemd/system/multi-user.target.wants/haproxy.service'
Allow HTTP service through Linux firewall.
[root@haproxy-01 ~]# firewall-cmd --permanent --add-service=http
success
[root@haproxy-01 ~]# firewall-cmd --reload
success
Test HAProxy Configuration:
Open the URL of the haproxy-01.example.com in a browser.
You may observe that the HTTP request has been served by webserver-01.example.com. It shows that our Load Balancer has forwarded the request to this server.
Press F5 to refresh the webpage.
Since, we have configured the roundrobin balancing in HAProxy. Therefore, it forwards next request to alternate server. You can refresh webpage multiple times to observe the functionality.
To see the detailed statistics of the HAProxy. Browse to http://haproxy-01.example.com/haproxy?stats.
We have successfully configured a HTTP Load Balancer with HAProxy.
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