Setting up IPVS Load Balancer with NGINX Application Servers

In this guide, we’ll set up an IPVS load balancer with one master node (Director) and two application servers running NGINX.

Prerequisites

Launch three machines:

• 1 IPVS Master Node (Director)
• 2 Application Servers running NGINX

Step 1: Install IPVSADM on the Master Node

IPVSADM is used to set up, maintain, or inspect the virtual server table in the Linux Kernel.

sudo apt update
sudo apt install ipvsadm -y

Step 2: Verify Application Servers

Ensure the application servers are running and accessible.

curl 192.168.144.101:80
curl 192.168.144.197:80

Step 3: Add Virtual Service

The -A option adds a virtual service.

• -t: Specifies TCP protocol
• -s: Scheduling algorithm (Round-Robin in this case)

sudo ipvsadm -A -t 192.168.0.117:80 -s rr

Step 4: Add Real Servers to the Virtual Service

The -a flag adds real servers.

• -r: Real server
• -m: Masquerading (NAT)

sudo ipvsadm -a -t 192.168.0.117:80 -r 192.168.144.101:80 -m
sudo ipvsadm -a -t 192.168.0.117:80 -r 192.168.144.197:80 -m

Step 6: Test the setup

Go to the Director node & hit it’s IP on port 80

curl 192.168.0.117:80

You will notice it will serve the request in round-robin fashion.

Step 6: List Virtual Server Table

Check the current virtual server configuration.

sudo ipvsadm -L

Example Output

IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
TCP  ip-192-168-0-117.ap-southeas rr
  -> ip-192-168-144-101.ap-southe Masq    1      0          0         
  -> ip-192-168-144-197.ap-southe Masq    1      0          0

Explanation

• LocalAddress:Port: ip-192-168-0-117 acts as the virtual IP (VIP) for your service.
• Scheduler (rr): Round-robin scheduling is being used.
• Forwarding Mode (Masq): The packets are being masqueraded (source NAT).
• Weight: 1 indicates equal weight for backend servers.
• ActiveConn/InActConn: Zero connections, meaning no traffic is currently hitting the service.

Step 7: List Connection Table of the IPVS Load Balancer

This command shows the IPVS connection entries.

sudo ipvsadm -lcn

Example Output

IPVS connection entries
pro expire state       source             virtual            destination
TCP 01:47  TIME_WAIT   192.168.0.117:39298 192.168.0.117:80   192.168.144.197:80
TCP 01:48  TIME_WAIT   192.168.0.117:49826 192.168.0.117:80   192.168.144.101:80

Explanation

• pro: Protocol (TCP in this case)
• expire: Time until connection entry expires
• state: State of the connection (e.g., TIME_WAIT)
• source: Source IP and port making the request
• virtual: Virtual service IP and port
• destination: Backend real server IP and port

Conclusion

This setup provides a simple and efficient load balancing mechanism using IPVS and ensures high availability for NGINX-based applications.