How To Setup LVS (Linux Virtual Server) Load Balancer on CentOS 8 / RHEL 8

Introduction:

Linux Virtual Server is a highly salable and highly available server built on a cluster of real servers with the load balance running on the Linux Operating System.
First of all we will install the Linux Virtual Server package on Our CentOS 8 / RHEL 8 machine. After Installing LVS on our Operating System we will configure it as a load balancer to the back end servers. This setup assumes you have installed a CentOS / RHEL 8 server or workstation edition.

Step 1: Installing Linux Virtual Server on CentOS 8 / RHEL 8

Run the following command on your server to Install Linux Virtual Server and Choose yes to proceed further.

[sabi@localhost ~]$ sudo yum install ipvsadm
 [sudo] password for sabi: 
 Last metadata expiration check: 3:38:25 ago on Sun 22 Dec 2019 12:37:06 AM EST.
 Dependencies resolved.
  Package          Arch            Version              Repository          Size
 Installing:
  ipvsadm          x86_64          1.29-8.el8           AppStream           57 k
 Transaction Summary
 Install  1 Package
 Total download size: 57 k
 Installed size: 83 k
 Is this ok [y/N]: y

Step 2: Enabling IP forwarding and enable service

When you have finished installing package, enable the service and IP forwarding in your machine.

echo 'net.ipv4.ip_forward = 1' | sudo tee -a /etc/sysctl.conf 
sudo sysctl -p 

Confirm it is turned to 1

[sabi@localhost ~]$ echo 'net.ipv4.ip forward = 1' | sudo tee -a /etc/sysctl.conf
[sudo] password for sabi: 
net.ipv4.ip forward = 1

Start and enable ipvsadm services by running

sudo touch /etc/sysconfig/ipvsadm
sudo systemctl enable –now ipvsadm

Check out the service status, it will be look like as:

[sabi@localhost ~]$ systemctl status ipvsadm
 ● ipvsadm.service - Initialise the Linux Virtual Server
    Loaded: loaded (/usr/lib/systemd/system/ipvsadm.service; enabled; vendor preset: di>
    Active: active (exited) since Sun 2019-12-22 04:25:30 EST; 20s ago
   Process: 5880 ExecStart=/bin/bash -c exec /sbin/ipvsadm-restore < /etc/sysconfig/ipv>
  Main PID: 5880 (code=exited, status=0/SUCCESS)
 Dec 22 04:25:29 localhost.localdomain systemd[1]: Starting Initialise the Linux Virtua>
 Dec 22 04:25:30 localhost.localdomain systemd[1]: Started Initialise the Linux Virtual>
 lines 1-8/8 (END)

Step 3: Configure LVS as Load Balancer

After setting up all, move forward to configure LVS as a load balancer to actual back-end applications.

Clean the IP tables rules by running

sudo ipvsadm -C

Step 4: Adding a Virtual Service

Add a virtual service by using the syntax

ipvsadm -A -t (ServiceIP:Port) -s (Distribution method)

Following Distribution methods supported:

• rr (Round Robin) = Equal load distribution among back-end servers
• wrr (Weighted Round Robin) = The Round Robin based on real Servers weight
• lc (Least Connection) = Servers having few active processes are selected for new load assignment on priority basis.
• wlc ( Weighted Least Connection) = Assigns tasks to servers with fewer jobs and relative to the real server’s weight (Ci/Wi) . By default, this method is used.

We will do configuration based on below diagram.

In this case, I’m setting LVS server to listen on 192.168.233.129 with port 80.

sudo ipvsadm -A -t 192.168.233.129:80 -s wlc

Now, add the back-end servers by typing

sudo ipvsadm -a -t (ServiceIP:Port) -r (BackendServerIP:Port) -m

The configuration will look like

sudo ipvsadm -a -t 192.168.233.129:80 -r 192.168.233.209:80 -m 
sudo ipvsadm -a -t 192.168.233.129:80 -r 192.168.233.4:80 -m 

Type the following command to list current rules:

[sabi@localhost ~]$ sudo ipvsadm -l 
 IP Virtual Server version 1.2.1 (size=4096)
 Prot LocalAddress:Port Scheduler Flags
   -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
 TCP  cent01:http wlc
   -> cent03:http                  Masq    1      0          0         
   -> cent02:http                  Masq    1      0          0      

Allow Firewall

sudo firewall-cmd --add-service=http --permanent
sudo firewall-cmd --reload

Now, when you load the LVS server IP / domain name from the browser, you will see the page on one of the back-end server.

Hi this is the LVS server page on back-end server 1

Upon reloading, the back-end server 2 page should show

Hi this is the LVS server page on back-end server 2

This is how you can set up your LVS server on CentOS 8 / RHEL 8.