4.1.2.2. Create VMs from Custom Images

💡 First Principle: Custom VM images enable deployment standardization by embedding pre-installed software, security baselines, and configurations into a reusable template, ensuring every new VM starts from a consistent, compliant state.

Scenario: Your organization has a standard build for web servers, including specific OS hardening, monitoring agents, and application runtime environments. You need to ensure that all new web server VMs are deployed with this exact configuration, consistently and efficiently.

What It Is: A custom image is a pre-configured Virtual Machine template that includes the operating system, applications, and any custom configurations.

Creating a Custom Image:

1. Prepare the source VM with required applications and settings.
2. Generalize the VM:
   • Windows: Run Sysprep to remove system-specific data.
   • Linux: Use waagent -deprovision+user to clean the VM.
3. Deallocate and mark the VM as generalized.
4. Capture the image.

Deploying from a Custom Image:

• When creating a new VM, select your managed image as the source.

Shared Image Gallery:

• Azure Shared Image Gallery allows you to manage, version, and share custom images across subscriptions and tenants.

Visual: Custom VM Image Workflow

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⚠️ Common Pitfall: Forgetting to generalize the source VM before capturing an image. This can lead to issues with unique identifiers (like SIDs on Windows) when deploying new VMs from the image.

Key Trade-Offs:

• Upfront Effort vs. Long-Term Consistency: Creating a custom image requires significant upfront effort but pays off in long-term consistency, speed of deployment, and reduced configuration errors.

Reflection Question: How does creating custom VM images (after generalizing the source VM) fundamentally enable organizations to standardize deployments, ensuring consistency and accelerating provisioning by embedding pre-installed software and security baselines?