Understanding Azure Machine Configuration

Azure Policy's machine configuration feature provides native capability to audit or configure operating system settings as code for machines running in Azure and hybrid Arc-enabled machines. You can use the feature directly per-machine, or orchestrate it at scale by using Azure Policy.

Configuration resources in Azure are designed as an extension resource. You can imagine each configuration as an extra set of properties for the machine. Configurations can include settings such as:

• Operating system settings
• Application configuration or presence
• Environment settings

Configurations are distinct from policy definitions. Machine configuration uses Azure Policy to dynamically assign configurations to machines. You can also assign configurations to machines manually, or by using other Azure services such as Automanage.

Examples of each scenario are provided in the following table.

You can view the per-setting results from configurations in the Guest assignments page. If an Azure Policy assignment orchestrated the configuration is orchestrated, you can select the "Last evaluated resource" link on the "Compliance details" page.

A video walk-through of this document is available. (Update coming soon)

Enable machine configuration

To manage the state of machines in your environment, including machines in Azure and Arc-enabled servers, review the following details.

Resource provider

Before you can use the machine configuration feature of Azure Policy, you must register the Microsoft.GuestConfiguration resource provider. If assignment of a machine configuration policy is done through the portal, or if the subscription is enrolled in Microsoft Defender for Cloud, the resource provider is registered automatically. You can manually register through the portal, Azure PowerShell, or Azure CLI.

Deploy requirements for Azure virtual machines

To manage settings inside a machine, a virtual machine extension is enabled and the machine must have a system-managed identity. The extension downloads applicable machine configuration assignments and the corresponding dependencies. The identity is used to authenticate the machine as it reads and writes to the machine configuration service. The extension isn't required for Arc-enabled servers because it's included in the Arc Connected Machine agent.

To deploy the extension at scale across many machines, assign the policy initiative Deploy prerequisites to enable Guest Configuration policies on virtual machines to a management group, subscription, or resource group containing the machines that you plan to manage.

If you prefer to deploy the extension and managed identity to a single machine, see Configure managed identities for Azure resources on a VM using the Azure portal.

To use machine configuration packages that apply configurations, Azure VM guest configuration extension version 1.26.24 or later is required.

Limits set on the extension

To limit the extension from impacting applications running inside the machine, the machine configuration agent isn't allowed to exceed more than 5% of CPU. This limitation exists for both built-in and custom definitions. The same is true for the machine configuration service in Arc Connected Machine agent.

Validation tools

Inside the machine, the machine configuration agent uses local tools to perform tasks.

The following table shows a list of the local tools used on each supported operating system. For built-in content, machine configuration handles loading these tools automatically.

Validation frequency

The machine configuration agent checks for new or changed guest assignments every 5 minutes. Once a guest assignment is received, the settings for that configuration are rechecked on a 15-minute interval. If multiple configurations are assigned, each is evaluated sequentially. Long-running configurations affect the interval for all configurations, because the next can't run until the prior configuration has finished.

Results are sent to the machine configuration service when the audit completes. When a policy evaluation trigger occurs, the state of the machine is written to the machine configuration resource provider. This update causes Azure Policy to evaluate the Azure Resource Manager properties. An on-demand Azure Policy evaluation retrieves the latest value from the machine configuration resource provider. However, it doesn't trigger a new activity within the machine. The status is then written to Azure Resource Graph.

Supported client types

Machine configuration policy definitions are inclusive of new versions. Older versions of operating systems available in Azure Marketplace are excluded if the Guest Configuration client isn't compatible. Additionally, Linux server versions that are out of lifetime support by their respective publishers are excluded from the support matrix.

The following table shows a list of supported operating systems on Azure images. The .x text is symbolic to represent new minor versions of Linux distributions.

* Red Hat CoreOS isn't supported.

Machine configuration policy definitions support custom virtual machine images as long as they're one of the operating systems in the previous table.

Network requirements

Azure virtual machines can use either their local virtual network adapter (vNIC) or Azure Private Link to communicate with the machine configuration service.

Azure Arc-enabled machines connect using the on-premises network infrastructure to reach Azure services and report compliance status.

Following is a list of the Azure Storage endpoints required for Azure and Azure Arc-enabled virtual machines to communicate with the machine configuration resource provider in Azure:

• oaasguestconfigac2s1.blob.core.windows.net
• oaasguestconfigacs1.blob.core.windows.net
• oaasguestconfigaes1.blob.core.windows.net
• oaasguestconfigases1.blob.core.windows.net
• oaasguestconfigbrses1.blob.core.windows.net
• oaasguestconfigbrss1.blob.core.windows.net
• oaasguestconfigccs1.blob.core.windows.net
• oaasguestconfigces1.blob.core.windows.net
• oaasguestconfigcids1.blob.core.windows.net
• oaasguestconfigcuss1.blob.core.windows.net
• oaasguestconfigeaps1.blob.core.windows.net
• oaasguestconfigeas1.blob.core.windows.net
• oaasguestconfigeus2s1.blob.core.windows.net
• oaasguestconfigeuss1.blob.core.windows.net
• oaasguestconfigfcs1.blob.core.windows.net
• oaasguestconfigfss1.blob.core.windows.net
• oaasguestconfiggewcs1.blob.core.windows.net
• oaasguestconfiggns1.blob.core.windows.net
• oaasguestconfiggwcs1.blob.core.windows.net
• oaasguestconfigjiws1.blob.core.windows.net
• oaasguestconfigjpes1.blob.core.windows.net
• oaasguestconfigjpws1.blob.core.windows.net
• oaasguestconfigkcs1.blob.core.windows.net
• oaasguestconfigkss1.blob.core.windows.net
• oaasguestconfigncuss1.blob.core.windows.net
• oaasguestconfignes1.blob.core.windows.net
• oaasguestconfignres1.blob.core.windows.net
• oaasguestconfignrws1.blob.core.windows.net
• oaasguestconfigqacs1.blob.core.windows.net
• oaasguestconfigsans1.blob.core.windows.net
• oaasguestconfigscuss1.blob.core.windows.net
• oaasguestconfigseas1.blob.core.windows.net
• oaasguestconfigsecs1.blob.core.windows.net
• oaasguestconfigsfns1.blob.core.windows.net
• oaasguestconfigsfws1.blob.core.windows.net
• oaasguestconfigsids1.blob.core.windows.net
• oaasguestconfigstzns1.blob.core.windows.net
• oaasguestconfigswcs1.blob.core.windows.net
• oaasguestconfigswns1.blob.core.windows.net
• oaasguestconfigswss1.blob.core.windows.net
• oaasguestconfigswws1.blob.core.windows.net
• oaasguestconfiguaecs1.blob.core.windows.net
• oaasguestconfiguaens1.blob.core.windows.net
• oaasguestconfigukss1.blob.core.windows.net
• oaasguestconfigukws1.blob.core.windows.net
• oaasguestconfigwcuss1.blob.core.windows.net
• oaasguestconfigwes1.blob.core.windows.net
• oaasguestconfigwids1.blob.core.windows.net
• oaasguestconfigwus2s1.blob.core.windows.net
• oaasguestconfigwus3s1.blob.core.windows.net
• oaasguestconfigwuss1.blob.core.windows.net

Communicate over virtual networks in Azure

To communicate with the machine configuration resource provider in Azure, machines require outbound access to Azure datacenters on port 443*. If a network in Azure doesn't allow outbound traffic, configure exceptions with Network Security Group rules. The service tags AzureArcInfrastructure and Storage can be used to reference the guest configuration and Storage services rather than manually maintaining the list of IP ranges for Azure datacenters. Both tags are required because Azure Storage hosts the machine configuration content packages.

Communicate over Private Link in Azure

Virtual machines can use private link for communication to the machine configuration service. Apply tag with the name EnablePrivateNetworkGC and value TRUE to enable this feature. The tag can be applied before or after machine configuration policy definitions are applied to the machine.

Traffic is routed using the Azure virtual public IP address to establish a secure, authenticated channel with Azure platform resources.

Communicate over public endpoints outside of Azure

Servers located on-premises or in other clouds can be managed with machine configuration by connecting them to Azure Arc.

For Azure Arc-enabled servers, allow traffic using the following patterns:

• Port: Only TCP 443 required for outbound internet access
• Global URL: *.guestconfiguration.azure.com

See the Azure Arc-enabled servers network requirements for a full list of all network endpoints required by the Azure Connected Machine Agent for core Azure Arc and machine configuration scenarios.

Communicate over Private Link outside of Azure

When you use private link with Arc-enabled servers, built-in policy packages are automatically downloaded over the private link. You don't need to set any tags on the Arc-enabled server to enable this feature.

Assigning policies to machines outside of Azure

The Audit policy definitions available for machine configuration include the Microsoft.HybridCompute/machines resource type. Any machines onboarded to Azure Arc-enabled servers that are in the scope of the policy assignment are automatically included.

Managed identity requirements

Policy definitions in the initiative Deploy prerequisites to enable guest configuration policies on virtual machines enable a system-assigned managed identity, if one doesn't exist. There are two policy definitions in the initiative that manage identity creation. The if conditions in the policy definitions ensure the correct behavior based on the current state of the machine resource in Azure.

If the machine doesn't currently have any managed identities, the effective policy is: Add system-assigned managed identity to enable Guest Configuration assignments on virtual machines with no identities

If the machine currently has a user-assigned system identity, the effective policy is: Add system-assigned managed identity to enable Guest Configuration assignments on VMs with a user-assigned identity

Availability

Customers designing a highly available solution should consider the redundancy planning requirements for virtual machines because guest assignments are extensions of machine resources in Azure. When guest assignment resources are provisioned into an Azure region that's paired, you can view guest assignment reports if at least one region in the pair is available. When the Azure region isn't paired and it becomes unavailable, you can't access reports for a guest assignment. When the region is restored, you can access the reports again.

It's best practice to assign the same policy definitions with the same parameters to all machines in the solution for highly available applications. This is especially true for scenarios where virtual machines are provisioned in Availability Sets behind a load balancer solution. A single policy assignment spanning all machines has the least administrative overhead.

For machines protected by Azure Site Recovery, ensure that the machines in the primary and secondary site are within scope of Azure Policy assignments for the same definitions. Use the same parameter values for both sites.

Data residency

Machine configuration stores and processes customer data. By default, customer data is replicated to the paired region. For the regions Singapore, Brazil South, and East Asia, all customer data is stored and processed in the region.

Troubleshooting machine configuration

For more information about troubleshooting machine configuration, see Azure Policy troubleshooting.

Multiple assignments

At this time, only some built-in machine configuration policy definitions support multiple assignments. However, all custom policies support multiple assignments by default if you used the latest version of the GuestConfiguration PowerShell module to create machine configuration packages and policies.

Following is the list of built-in machine configuration policy definitions that support multiple assignments:

Assignments to Azure management groups

Azure Policy definitions in the category Guest Configuration can be assigned to management groups when the effect is AuditIfNotExists or DeployIfNotExists.

Client log files

The machine configuration extension writes log files to the following locations:

Windows

• Azure VM: C:\ProgramData\GuestConfig\gc_agent_logs\gc_agent.log
• Arc-enabled server: C:\ProgramData\GuestConfig\arc_policy_logs\gc_agent.log

Linux

• Azure VM: /var/lib/GuestConfig/gc_agent_logs/gc_agent.log
• Arc-enabled server: /var/lib/GuestConfig/arc_policy_logs/gc_agent.log

Collecting logs remotely

The first step in troubleshooting machine configurations or modules should be to use the cmdlets following the steps in How to test machine configuration package artifacts. If that isn't successful, collecting client logs can help diagnose issues.

Windows

Capture information from log files using Azure VM Run Command, the following example PowerShell script can be helpful.

$linesToIncludeBeforeMatch = 0
$linesToIncludeAfterMatch  = 10
$params = @{
    Path = 'C:\ProgramData\GuestConfig\gc_agent_logs\gc_agent.log'
    Pattern = @(
        'DSCEngine'
        'DSCManagedEngine'
    )
    CaseSensitive = $true
    Context = @(
        $linesToIncludeBeforeMatch
        $linesToIncludeAfterMatch
    )
}
Select-String @params | Select-Object -Last 10

Linux

Capture information from log files using Azure VM Run Command, the following example Bash script can be helpful.

LINES_TO_INCLUDE_BEFORE_MATCH=0
LINES_TO_INCLUDE_AFTER_MATCH=10
LOGPATH=/var/lib/GuestConfig/gc_agent_logs/gc_agent.log
egrep -B $LINES_TO_INCLUDE_BEFORE_MATCH -A $LINES_TO_INCLUDE_AFTER_MATCH 'DSCEngine|DSCManagedEngine' $LOGPATH | tail

Agent files

The machine configuration agent downloads content packages to a machine and extracts the contents. To verify what content has been downloaded and stored, view the folder locations in the following list.

• Windows: C:\ProgramData\guestconfig\configuration
• Linux: /var/lib/GuestConfig/Configuration

Open-source nxtools module functionality

A new open-source nxtools module has been released to help make managing Linux systems easier for PowerShell users.

The module helps in managing common tasks such as:

• Managing users and groups
• Performing file system operations
• Managing services
• Performing archive operations
• Managing packages

The module includes class-based DSC resources for Linux and built-in machine configuration packages.

To provide feedback about this functionality, open an issue on the documentation. We currently don't accept PRs for this project, and support is best effort.

Machine configuration samples

Machine configuration built-in policy samples are available in the following locations:

• Built-in policy definitions - Guest Configuration
• Built-in initiatives - Guest Configuration
• Azure Policy samples GitHub repository
• Sample DSC resource modules

Next steps

• Set up a custom machine configuration package development environment.
• Create a package artifact for machine configuration.
• Test the package artifact from your development environment.
• Use the GuestConfiguration module to create an Azure Policy definition for at-scale management of your environment.
• Assign your custom policy definition using Azure portal.
• Learn how to view compliance details for machine configuration policy assignments.