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2. Provision an Application Gateway.

Overview

In this exercise, you will extend the environment you created in the previous Provision VMSS with LB by adding an Azure Application Gateway (AGW)—a Layer 7 load balancer. The AGW will distribute HTTP traffic to the VM instances created earlier. You will create a new subnet specifically for the AGW and configure it to route requests to the VMSS backend.

💡 Prerequisite
Make sure you have completed the Provision VMSS with LB exercise, including its Resource Group, VNet, and VM Scale Set.

Step 1: Log in to Azure Portal

  1. Open a web browser and navigate to the Azure Portal.
  2. Sign in with your Azure account credentials.

Step 2: Add a New Subnet for the Application Gateway

  1. In the Azure Portal, search for “Virtual networks”.
  2. Select the existing VNet you created for your VM Scale Set (e.g., LabVMSSVnet).
  3. Under Settings, click Subnets.
  4. Click + Subnet, then create a new subnet:
    • Name: AGWSubnet
    • Address range: A suitable CIDR block (for example 10.0.1.0/24 if your VNet range allows).
  5. Click Save.

💡 Information

The Application Gateway must exist in its own dedicated subnet separate from your VMSS instances. This step ensures it has an isolated subnet to operate in.

Step 3: Create an Azure Application Gateway

  1. In the Azure Portal, search for “Application gateways” and click “Create”.
  2. Under Basics:
    • Subscription: Select the same subscription used for your VMSS.
    • Resource group: Pick the same resource group, e.g. LabResourceGroup.
    • Name: LabAppGw.
    • Region: Must match the region of your existing resources (e.g. North Europe).
    • Tier: Basic (suitable for development).
    • Virtual network: Choose the one created earlier
    • Subnet: AGWSubnet
  3. Under Frontend:
    • Add a new Public IP address:
      • Name: LabAppGwPublicIP.
      • OK
  4. Under Backends:
    • Add a backend pool:
      • Name: LabAppGwBackendPool.
      • For Target type, select VMSS and choose your existing VM scale set (LabVMSS).
      • Add
  5. Under Configuration:
    • Add a routing rule:
      1. Rule name: HTTPRule.
      2. Priority: 100
      3. Listener:
        • Listener name: HTTPlistener.
        • Frontend IP: LabAppGwPublicIP (your newly created/selected IP).
        • Protocol: HTTP.
        • Port: 80.
      4. Backend target: - Backend pool: LabAppGwBackendPool. - Backend settings: Add new - Backend settings name: HTTPsetting - Add
    • Click Add to finalize your rule.
  6. Click Review + create. After validation, click Create to provision the Application Gateway.

✅ Verification Step:

  • Once deployment completes, go to Application gateways > LabAppGw and confirm the status is Running.
  • Make sure the AGW is deployed into the AGWSubnet you created in the previous step.

✅ Verify Application Gateway Routing

  1. In LabAppGw, note the Frontend public IP address (under the Overview tab).
  2. Open a web browser and navigate to that public IP.
  3. You should see the Nginx welcome page, with the randomized numbers that indicate which VM instance you’ve landed on.
  4. Refresh the page multiple times; traffic should distribute across the VM instances in your VM Scale Set.

✅ Verification Step
If you scale your VMSS up or down, the AGW will automatically include or remove instances from the backend pool, continuing to distribute traffic at the application layer.

💡 Information
The Azure Application Gateway provides Layer 7 (HTTP/HTTPS) load-balancing features, allowing you to do URL-based routing, path-based routing, and more advanced HTTP features compared to the Layer 4 Azure Load Balancer.

Conclusion

By completing this exercise, you have:

(Optional) Clean Up Resources

If you want to remove the entire lab environment (both the VMSS and the Application Gateway):

  1. In the Azure Portal, search for “Resource Groups”.
  2. Locate LabResourceGroup (or the name you chose).
  3. Click Delete resource group, type the name to confirm, then select Delete.

Happy Cloud!