Guide: Load Balancers

This guide walks through creating a private network, two web server VMs, and exposing them via an OpenStack load balancer. It covers network creation, VM provisioning, floating IP assignment, basic web server setup, and load balancer configuration and testing.

Network Setup

Create a private network

openstack network create myNet

Create a subnet of the private network

openstack subnet create myNet_v4 --network myNet --subnet-range 192.168.100.0/24

Create a router and connect it to a public network

openstack router create myRouter
openstack router add subnet myRouter myNet_v4
openstack router set myRouter --external-gateway provider_net

Creating Backend Instances for Load Balancing

As an example, we create two identical web server instances that will serve as backend nodes for the load balancer.

Create two identical VMs

openstack server create \
  --image ubuntu-24.04 \
  --flavor m1.small \
  --network myNet \
  --key-name myKey \
  --min 2 --max 2 \
  webserver

Associate (temporary) floating IPs to make the VMs accessible

FIP1=$(openstack floating ip create provider_net -f value -c floating_ip_address)
FIP2=$(openstack floating ip create provider_net -f value -c floating_ip_address)

openstack server add floating ip webserver-1 $FIP1
openstack server add floating ip webserver-2 $FIP2

Install basic web servers on the VMs

SSH into each VM and run:

sudo apt update && \
sudo apt -y install apache2 && \
sudo systemctl enable --now apache2 && \
echo $(hostname) | sudo tee /var/www/html/index.html

Add security rules to allow HTTP access on port 80 as described in the section on Security Rules.

Test the web servers:

curl $FIP1
# Expected output: webserver-1

Load Balancer Setup and Backend Integration

Create the load balancer

openstack loadbalancer create \
  --name myLB \
  --vip-subnet-id myNet_v4 \
  --provider ovn

Create a listener on port 80

openstack loadbalancer listener create \
    --name myListener \
    --protocol TCP \
    --protocol-port 80 \
    myLB

Create a pool for the listener

openstack loadbalancer pool create \
    --name myPool \
    --listener myListener \
    --protocol TCP \
    --lb-algorithm SOURCE_IP_PORT

Add web servers to the pool

Get the subnet ID and VM IPs in it:

SUBNET_ID=$(openstack subnet list --name myNet_v4 -f value -c ID)
WEB1_IP=$(openstack server show webserver-1 -f value -c addresses | grep -o '192\.168\.100\.[0-9]\+')
WEB2_IP=$(openstack server show webserver-2 -f value -c addresses | grep -o '192\.168\.100\.[0-9]\+')

Add each VM to the pool:

openstack loadbalancer member create \
    --subnet-id $SUBNET_ID \
    --address $WEB1_IP \
    --protocol-port 80 \
    myPool

openstack loadbalancer member create \
    --subnet-id $SUBNET_ID \
    --address $WEB2_IP \
    --protocol-port 80 \
    myPool

Assign a floating IP to the load balancer

Create a floating IP and associate it with the VIP of the load balancer:

FIP=$(openstack floating ip create provider_net -f value -c floating_ip_address)
VIPPORT=$(openstack loadbalancer show myLB -f value -c vip_port_id)
openstack floating ip set --port $VIPPORT $FIP

Test the load balancer:

curl $FIP

Expected output (may alternate between VMs): webserver-1 / webserver-2