Tutorial: Install applications in Virtual Machine Scale Sets with the Azure CLI

To run applications on virtual machine (VM) instances in a scale set, you first need to install the application components and required files. In a previous tutorial, you learned how to create and use a custom VM image to deploy your VM instances. This custom image included manual application installs and configurations. You can also automate the install of applications to a scale set after each VM instance is deployed, or update an application that already runs on a scale set. In this tutorial you learn how to:

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

Prerequisites

• If you prefer to run CLI reference commands locally, install the Azure CLI. If you're running on Windows or macOS, consider running Azure CLI in a Docker container. For more information, see How to run the Azure CLI in a Docker container.

  • If you're using a local installation, sign in to the Azure CLI by using the az login command. To finish the authentication process, follow the steps displayed in your terminal. For other sign-in options, see Sign in with the Azure CLI.

  • When you're prompted, install the Azure CLI extension on first use. For more information about extensions, see Use extensions with the Azure CLI.

  • Run az version to find the version and dependent libraries that are installed. To upgrade to the latest version, run az upgrade.

• This article requires version 2.0.29 or later of the Azure CLI.

What is the Azure Custom Script Extension?

The Custom Script Extension downloads and executes scripts on Azure VMs. This extension is useful for post deployment configuration, software installation, or any other configuration / management task. Scripts can be downloaded from Azure storage or GitHub, or provided to the Azure portal at extension run-time.

The Custom Script extension integrates with Azure Resource Manager templates, and can also be used with the Azure CLI, Azure PowerShell, Azure portal, or the REST API. For more information, see the Custom Script Extension overview.

To use the Custom Script Extension with the Azure CLI, you create a JSON file that defines what files to obtain and commands to execute. These JSON definitions can be reused across scale set deployments to apply consistent application installs.

Create Custom Script Extension definition

To see the Custom Script Extension in action, let's create a scale set that installs the NGINX web server and outputs the hostname of the scale set VM instance. The following Custom Script Extension definition downloads a sample script from GitHub, installs the required packages, then writes the VM instance hostname to a basic HTML page.

In your current shell, create a file named customConfig.json and paste the following configuration.

{
  "fileUris": ["https://raw.githubusercontent.com/Azure-Samples/compute-automation-configurations/master/automate_nginx.sh"],
  "commandToExecute": './automate_nginx.sh'
}

Create a scale set

Create a resource group with az group create. The following example creates a resource group named myResourceGroup in the chinanorth2 location:

az group create --name myResourceGroup --location chinanorth2

Now create a Virtual Machine Scale Set with az vmss create. The following example creates a scale set named myScaleSet, and generates SSH keys if they do not exist:

az vmss create \
  --resource-group myResourceGroup \
  --name myScaleSet \
  --image Ubuntu2204 \
  --orchestration-mode Flexible \
  --admin-username azureuser \
  --generate-ssh-keys

It takes a few minutes to create and configure all the scale set resources and VMs.

Apply the Custom Script Extension

Apply the Custom Script Extension configuration to the VM instances in your scale set with az vmss extension set. The following example applies the customConfig.json configuration to the myScaleSet VM instances in the resource group named myResourceGroup:

az vmss extension set \
  --publisher Microsoft.Azure.Extensions \
  --version 2.0 \
  --name CustomScript \
  --resource-group myResourceGroup \
  --vmss-name myScaleSet \
  --settings customConfig.json

Apply the extension to the existing scale set instances

Upgrade all the instances to apply the custom script. The upgrade may take a couple of minutes.

az vmss update-instances --resource-group myResourceGroup --name myScaleSet --instance-ids "*"

Allow traffic to port 80

To allow traffic to flow through the load balancer to the virtual machines the default network security group needs to be updated.

az network nsg rule create --name AllowHTTP --resource-group myResourceGroup --nsg-name myScaleSetNSG --access Allow --priority 1010 --destination-port-ranges 80 

Test your scale set

To see your web server in action, obtain the public IP address of your load balancer with az network public-ip show. The following example obtains the IP address for myScaleSetLBPublicIP created as part of the scale set:

az network public-ip show \
  --resource-group myResourceGroup \
  --name myScaleSetLBPublicIP \
  --query [ipAddress] \
  --output tsv

Enter the public IP address of the load balancer in to a web browser. The load balancer distributes traffic to one of your VM instances, as shown in the following example:

Leave the web browser open so that you can see an updated version in the next step.

Change the upgrade policy

In the previous section, in order to apply the updated application to all the scale set instances, a manual upgrade was needed. To enable updates to be applied automatically to all existing scale set instances, update the upgrade policy from manual to automatic. For more information on upgrade policies, see Upgrade policies for Virtual Machine Scale Sets.

az vmss update \
    --name myScaleSet \
    --resource-group myResourceGroup \
    --set upgradePolicy.mode=automatic

Update app deployment

In your current shell, create a file named customConfigv2.json and paste the following configuration. This definition runs an updated v2 version of the application install script:

{
  "fileUris": ["https://raw.githubusercontent.com/Azure-Samples/compute-automation-configurations/master/automate_nginx_v2.sh"],
  "commandToExecute": "./automate_nginx_v2.sh"
}

Apply the Custom Script Extension configuration to the your scale set again with az vmss extension set. The customConfigv2.json is used to apply the updated version of the application:

az vmss extension set \
  --publisher Microsoft.Azure.Extensions \
  --version 2.0 \
  --name CustomScript \
  --resource-group myResourceGroup \
  --vmss-name myScaleSet \
  --settings @customConfigv2.json

Because the scale set is now using an automatic upgrade policy, the updated application will automatically be applied to existing scale set instances. Refresh your web browser to see the updated application.

Clean up resources

To remove your scale set and additional resources, delete the resource group and all its resources with az group delete. The --no-wait parameter returns control to the prompt without waiting for the operation to complete. The --yes parameter confirms that you wish to delete the resources without an additional prompt to do so.

az group delete --name myResourceGroup --no-wait --yes

Next steps

In this tutorial, you learned how to automatically install and update applications on your scale set with the Azure CLI:

Advance to the next tutorial to learn how to automatically scale your scale set.