Use an Azure CLI sample script to load balance traffic between highly available virtual machines

This script sample creates everything needed to run several Ubuntu virtual machines configured in a highly available and load balanced configuration. After running the script, you will have three virtual machines, joined to an Azure Availability Set, and accessible through an Azure Load Balancer.

To run this sample, install the latest version of the Azure CLI. To start, run az login to create a connection with Azure.

Samples for the Azure CLI are written for the bash shell. To run this sample in Windows PowerShell or Command Prompt, you may need to change elements of the script.

If you don't have an Azure subscription, create a free account before you begin.

Sample script

#!/bin/bash

# Update for your admin password
AdminPassword=ChangeYourAdminPassword1

# Create a resource group.
az group create --name myResourceGroup --location westus

# Create a virtual network.
az network vnet create --resource-group myResourceGroup --name myVnet \
  --address-prefix 192.168.0.0/16 --subnet-name mySubnet --subnet-prefix 192.168.1.0/24

# Create a public IP address.
az network public-ip create --resource-group myResourceGroup --name myPublicIP

# Create an Azure Load Balancer.
az network lb create --resource-group myResourceGroup --name myLoadBalancer --public-ip-address myPublicIP \
  --frontend-ip-name myFrontEndPool --backend-pool-name myBackEndPool

# Creates an LB probe on port 80.
az network lb probe create --resource-group myResourceGroup --lb-name myLoadBalancer \
  --name myHealthProbe --protocol tcp --port 80

# Creates an LB rule for port 80.
az network lb rule create --resource-group myResourceGroup --lb-name myLoadBalancer --name myLoadBalancerRuleWeb \
  --protocol tcp --frontend-port 80 --backend-port 80 --frontend-ip-name myFrontEndPool \
  --backend-pool-name myBackEndPool --probe-name myHealthProbe

# Create three NAT rules for port 3389.
for i in `seq 1 3`; do
  az network lb inbound-nat-rule create \
    --resource-group myResourceGroup --lb-name myLoadBalancer \
    --name myLoadBalancerRuleSSH$i --protocol tcp \
    --frontend-port 422$i --backend-port 3389 \
    --frontend-ip-name myFrontEndPool
done

# Create a network security group
az network nsg create --resource-group myResourceGroup --name myNetworkSecurityGroup

# Create a network security group rule for port 3389.
az network nsg rule create --resource-group myResourceGroup --nsg-name myNetworkSecurityGroup --name myNetworkSecurityGroupRuleSSH \
  --protocol tcp --direction inbound --source-address-prefix '*' --source-port-range '*'  \
  --destination-address-prefix '*' --destination-port-range 3389 --access allow --priority 1000

# Create a network security group rule for port 80.
az network nsg rule create --resource-group myResourceGroup --nsg-name myNetworkSecurityGroup --name myNetworkSecurityGroupRuleHTTP \
--protocol tcp --direction inbound --priority 1001 --source-address-prefix '*' --source-port-range '*' \
--destination-address-prefix '*' --destination-port-range 80 --access allow --priority 2000

# Create three virtual network cards and associate with public IP address and NSG.
for i in `seq 1 3`; do
  az network nic create \
    --resource-group myResourceGroup --name myNic$i \
    --vnet-name myVnet --subnet mySubnet \
    --network-security-group myNetworkSecurityGroup --lb-name myLoadBalancer \
    --lb-address-pools myBackEndPool --lb-inbound-nat-rules myLoadBalancerRuleSSH$i
done

# Create an availability set.
az vm availability-set create --resource-group myResourceGroup --name myAvailabilitySet --platform-fault-domain-count 3 --platform-update-domain-count 3

# Create three virtual machines.
for i in `seq 1 3`; do
  az vm create \
    --resource-group myResourceGroup \
    --name myVM$i \
    --availability-set myAvailabilitySet \
    --nics myNic$i \
    --image win2016datacenter \
    --admin-password $AdminPassword \
    --admin-username azureuser \
    --no-wait
done

Clean up deployment

Run the following command to remove the resource group, VM, and all related resources.

az group delete --name myResourceGroup --yes

Script explanation

This script uses the following commands to create a resource group, virtual machine, availability set, load balancer, and all related resources. Each command in the table links to command specific documentation.

Command Notes
az group create Creates a resource group in which all resources are stored.
az network vnet create Creates an Azure virtual network and subnet.
az network public-ip create Creates a public IP address with a static IP address and an associated DNS name.
az network lb create Creates an Azure Network Load Balancer (NLB).
az network lb probe create Creates an NLB probe. An NLB probe is used to monitor each VM in the NLB set. If any VM becomes inaccessible, traffic is not routed to the VM.
az network lb rule create Creates an NLB rule. In this sample, a rule is created for port 80. As HTTP traffic arrives at the NLB, it is routed to port 80 one of the VMs in the NLB set.
az network lb inbound-nat-rule create Creates an NLB Network Address Translation (NAT) rule. NAT rules map a port of the NLB to a port on a VM. In this sample, a NAT rule is created for SSH traffic to each VM in the NLB set.
az network nsg create Creates a network security group (NSG), which is a security boundary between the internet and the virtual machine.
az network nsg rule create Creates an NSG rule to allow inbound traffic. In this sample, port 22 is opened for SSH traffic.
az network nic create Creates a virtual network card and attaches it to the virtual network, subnet, and NSG.
az vm availability-set create Creates an availability set. Availability sets ensure application uptime by spreading the virtual machines across physical resources such that if failure occurs, the entire set is not effected.
az vm create Creates the virtual machine and connects it to the network card, virtual network, subnet, and NSG. This command also specifies the virtual machine image to be used and administrative credentials.
az group delete Deletes a resource group including all nested resources.

Next steps

For more information on the Azure CLI, see Azure CLI documentation.

Additional virtual machine CLI script samples can be found in the Azure Windows VM documentation.