Custom Script Extension vs Run Command for VM Configuration

Bombbe 1,441

What are the differences and use cases for Custom Script Extension and Run Command when configuring virtual machines after deployment? Both options seem to achieve similar results, but it's challenging to find clear guidance or examples for choosing one over the other. Any tips or insights would be nice to have

Akpesiri Ogbebor 700

Hello @Bombbe

Thank you for contacting Microsoft QnA.

Custom Script Extension and Run Command are tools Azure provides to execute scripts or commands on virtual machines after deployment. While they seem similar, they serve slightly different purposes and have unique use cases. Here's a breakdown of their differences and recommendations for when to use each:

Custom Script Extension

Overview:

Custom Script Extension is a VM extension that allows you to download and execute scripts on a VM. The scripts can be hosted in Azure Storage, GitHub, or other accessible locations.
It's commonly used during the initial configuration or post-deployment configuration of a VM.

Key Features:

Script Persistence: The script is downloaded to the VM, so you can refer to it later if needed.
Ideal for Automation: Frequently used in automated deployment workflows, such as ARM templates, Bicep, or Terraform.
Repeatable Configurations: Can be reused across multiple VMs with consistent results.

Common Use Cases:

Installing software after VM deployment.
Configuring VM settings during provisioning.
Running configuration management tools like Ansible or Chef bootstrap scripts.
Deploying application code from GitHub or other sources.

Limitations:

Requires an external source for the script (e.g., Azure Storage or GitHub).
Not designed for one-off, interactive troubleshooting or quick commands. Custom Script Extension Overview:
- Custom Script Extension is a VM extension that allows you to download and execute scripts on a VM. The scripts can be hosted in Azure Storage, GitHub, or other accessible locations.
- It's commonly used during the initial configuration or post-deployment configuration of a VM.
Key Features:
1. Script Persistence: The script is downloaded to the VM, so you can refer to it later if needed.
2. Ideal for Automation: Frequently used in automated deployment workflows, such as ARM templates, Bicep, or Terraform.
3. Repeatable Configurations: Can be reused across multiple VMs with consistent results.
Common Use Cases:
- Installing software after VM deployment.
- Configuring VM settings during provisioning.
- Running configuration management tools like Ansible or Chef bootstrap scripts.
- Deploying application code from GitHub or other sources.
Limitations:
- Requires an external source for the script (e.g., Azure Storage or GitHub).
- Not designed for one-off, interactive troubleshooting or quick commands.

Run Command

Overview:

Run Command is a service that allows you to run commands directly on a VM from the Azure portal, Azure CLI, or REST API.
It's more interactive and is ideal for on-demand operations or troubleshooting.

Key Features:

No Script Hosting Required: You can run commands directly without needing to host a script externally.
Interactive Use: Useful for quick fixes, ad-hoc commands, and debugging.
Portal Integration: Accessible via the Azure portal for immediate execution.
Broad Support: Can execute shell commands (Linux) or PowerShell commands (Windows).

Common Use Cases:

Ad-hoc troubleshooting or diagnostics (e.g., checking system status, restarting services).
Running commands to update configurations or resolve issues without direct VM login.
Temporary changes or small configurations that don’t need to be automated.

Limitations:

Commands are not automatically stored or versioned, making it less suitable for reusable configurations.
Not as seamless for large or complex configurations compared to Custom Script Extension. Run Command Overview:
- Run Command is a service that allows you to run commands directly on a VM from the Azure portal, Azure CLI, or REST API.
- It's more interactive and is ideal for on-demand operations or troubleshooting.
Key Features:
1. No Script Hosting Required: You can run commands directly without needing to host a script externally.
2. Interactive Use: Useful for quick fixes, ad-hoc commands, and debugging.
3. Portal Integration: Accessible via the Azure portal for immediate execution.
4. Broad Support: Can execute shell commands (Linux) or PowerShell commands (Windows).
Common Use Cases:
- Ad-hoc troubleshooting or diagnostics (e.g., checking system status, restarting services).
- Running commands to update configurations or resolve issues without direct VM login.
- Temporary changes or small configurations that don’t need to be automated.
Limitations:
- Commands are not automatically stored or versioned, making it less suitable for reusable configurations.
- Not as seamless for large or complex configurations compared to Custom Script Extension.

When to Use Which

Criteria	Custom Script Extension	Run Command
Use Case	Initial or automated configuration of VMs.	Ad-hoc tasks, diagnostics, and quick fixes.
Use Case	Initial or automated configuration of VMs.	Ad-hoc tasks, diagnostics, and quick fixes.
Automation	Best suited for IaC workflows or consistent setups.	Less suited for automation but good for interactive use.
Script Persistence	Scripts are downloaded and stored on the VM.	Commands are executed directly and not stored.
Ease of Use	Requires pre-hosted scripts and configuration.	Very straightforward and requires no external resources.
Scalability	Ideal for scalable deployments across multiple VMs.	Best for individual VM operations.

Tips for Choosing

For initial setup or deploying consistent configurations across multiple VMs, use Custom Script Extension.
For one-off fixes, diagnostics, or when you're troubleshooting an issue, use Run Command.
If you're integrating with IaC (ARM templates, Terraform, etc.), prefer Custom Script Extension as it fits well with automation pipelines.
For debugging a single VM without logging in, Run Command offers convenience without requiring prior setup.

You can mark it 'Accept Answer' and 'Upvote' if this helped you

Siri

Srinud 3,585 Reputation points Microsoft Vendor

2025-01-23T17:49:20.5566667+00:00

Hi Bombbe,
I Hope you are doing well!!

I just wanted to check if you had a chance to review answer. If you found it helpful, could you kindly click the “Upvote” on my post. This will help increase its visibility of this question for other members of the Microsoft Q&A community.

If you have any further queries, please let us know in the comment.

Thank you.

1 answer

Srinud 3,585 Reputation points Microsoft Vendor

2025-01-22T02:38:04.48+00:00
Hi Bombbe,
Thank you for reaching out to us on the Microsoft Q&A forum.
The Custom Script Extension and Run Command are both options for configuring virtual machines after deployment, but they serve different purposes and are suited to different scenarios.

The Custom Script Extension offers a more flexible and comprehensive solution for executing custom scripts (like PowerShell, Bash) directly on a virtual machine after its deployment. This extension is particularly designed for tasks involving the execution of scripts to configure software, install dependencies, or modify system settings.

Run Command is a feature available through the Azure portal that enables the execution of scripts or commands directly on a virtual machine without requiring user login. This functionality allows for the execution of predefined or custom scripts on the VM without the need to deploy or manage additional extensions. it is particularly suitable for ad hoc or quick configuration tasks.

Please find the document below for more information:

Custom Script Extension for Windows

Run Command for Windows VMs

If the information is helpful, please consider by clicking the "Accept answer and Upvote" on the post. If you have any further queries, please let us know in the comment.
Please sign in to rate this answer.
Srinud 3,585 Reputation points Microsoft Vendor

2025-01-24T16:34:29.0733333+00:00

Hi Bombbe,

I just wanted to check if you had a chance to review answer. If you found it helpful, could you kindly click the “Accept answer and Upvote” on my post. This will help increase its visibility of this question for other members of the Microsoft Q&A community.

If you have any further queries, please let us know in the comment.

Thank you.
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