Introduction

Azure simplifies the standardization, replication, and scaling of virtual machines through the integrated use of the Azure Compute Gallery and Virtual Machine Scale Sets (VMSS). This powerful combination allows you to capture a pre-configured virtual machine as a reusable image, store it centrally in a Compute Gallery, and then deploy multiple identical VMs or entire scale sets with minimal effort. This guide provides a hands-on walkthrough of the essential steps involved.

We will cover:

  • Creating an Azure Compute Gallery.
  • Capturing a VM image and saving it to the gallery.
  • Deploying a Virtual Machine Scale Set using a gallery image.
  • Configuring scaling policies to dynamically manage resources based on demand.

By completing this guide, you will gain proficiency in efficiently managing reusable VM images and orchestrating resource scaling to meet fluctuating workload requirements.

Prerequisites

Before you begin, ensure you have the following:

  • An active Azure subscription.
  • The Azure CLI installed and configured, or access to the Azure portal.
  • Basic understanding of Azure Virtual Machines and networking concepts.

Creating an Azure Compute Gallery

The Azure Compute Gallery acts as a central repository for managing and sharing VM images. It provides versioning, regional replication, and access control for your images.

Steps to Create a Compute Gallery:

  1. Log in to the Azure portal.
  2. Navigate to Compute Galleries. Search for "Compute Galleries" in the top search bar and select it.
  3. Click "Create". This will open the "Create a Compute Gallery" blade.
  4. Configure Basic Settings:
    • Subscription: Select your Azure subscription.
    • Resource Group: Choose an existing resource group or create a new one.
    • Gallery name: Provide a unique name for your gallery (e.g., my-app-gallery).
    • Region: Select the Azure region where you want to deploy the gallery.
  5. Review and Create. Once configured, click "Review + create" and then "Create" to deploy the gallery.

Capturing a VM Image

Once your Compute Gallery is set up, you can capture an existing or newly provisioned VM as an image. This image will be stored as an Image Version within an Image Definition inside your gallery.

Steps to Capture an Image:

  1. Prepare your Source VM: Ensure the VM you want to capture is generalized (Sysprep for Windows, waagent -deprovision for Linux) to remove machine-specific information. Shut down the VM.
  2. Navigate to your VM in the Azure portal.
  3. Click "Capture". This option is usually found in the "Operations" section of the VM blade.
  4. Configure Image Settings:
    • Automatically delete this virtual machine after creating the image: Select "Yes" if you no longer need the original VM.
    • Yes, share it to a gallery as a managed image: Select this option.
    • Target Azure Compute Gallery: Choose the gallery you created earlier (e.g., my-app-gallery).
    • Target Image Definition: Click "Create new" to define your image. Provide a name (e.g., my-web-app-image), operating system type, and OS state (Generalized or Specialized).
    • Target Image Version: Provide a version number (e.g., 1.0.0). You can also specify replica regions.
  5. Create. Click "Review + create" and then "Create" to start the image capture process. This can take some time depending on the VM size and data.
Azure portal interface for capturing a virtual machine image into a Compute Gallery.

Creating a Virtual Machine Scale Set (VMSS)

Virtual Machine Scale Sets allow you to deploy and manage a set of identical, load-balanced VMs. They automatically scale based on demand and can be configured to use images from your Compute Gallery.

Steps to Create a VM Scale Set:

  1. Navigate to Virtual Machine Scale Sets in the Azure portal. Search for "Virtual Machine Scale Sets" and select it.
  2. Click "Create".
  3. Configure Basic Settings:
    • Subscription and Resource Group.
    • Name: Provide a name for your scale set (e.g., my-web-app-vmss).
    • Region: Select the same region as your gallery or a replica region.
    • Availability Zone: Choose your desired availability zones for resilience.
    • Orchestration mode: Select "Uniform" for identical VMs.
    • Image type: Choose "Select from your images".
    • Image: Browse and select the Image Definition and Image Version you created in the Compute Gallery (e.g., my-web-app-image, version 1.0.0).
  4. Configure Instance Details:
    • Scale factor: Set the initial number of VM instances (e.g., 2).
    • VM size: Choose an appropriate VM size.
  5. Configure Networking:
    • Virtual network: Select or create a VNet.
    • Load balancer: Choose "Create new" or select an existing load balancer to distribute traffic across instances.
  6. Configure Scaling: This is a crucial step for managing demand. You can set up autoscale rules.
    • Initial instance count: Set the base number of instances.
    • Minimum number of instances: Define the lowest number of instances to maintain.
    • Maximum number of instances: Set the upper limit for scaling out.
    • Scale out/in rules: Configure rules based on metrics like CPU percentage or network in/out. For example, scale out to 5 instances when CPU exceeds 70% for 10 minutes, and scale in to 2 instances when CPU drops below 30% for 15 minutes.
  7. Review and Create. Complete the configuration and click "Review + create", then "Create". Azure will provision the scale set and its initial instances.

Managing and Monitoring Scale Sets

Once deployed, you can manage and monitor your VM Scale Set through the Azure portal or Azure CLI.

  • Scaling: Adjust the instance count manually or let autoscale rules manage it. You can view current instance counts and monitor scaling events.
  • Instance Health: Check the health of individual VM instances within the scale set.
  • Updates: You can update the scale set to use a newer version of your gallery image. This process involves rolling out the update to existing instances.
  • Monitoring: Utilize Azure Monitor to track performance metrics, logs, and set up alerts for key indicators like CPU usage, memory, and network traffic.

By mastering Azure Compute Gallery and Virtual Machine Scale Sets, you establish a robust, scalable, and efficient infrastructure for deploying and managing your applications.