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Remediation options for machine configuration

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Before you begin, it's a good idea to read the overview page for machine configuration.

Important

The machine configuration extension is required for Azure virtual machines. To deploy the extension at scale across all machines, assign the following policy initiative: Deploy prerequisites to enable guest configuration policies on virtual machines

To use machine configuration packages that apply configurations, Azure VM guest configuration extension version 1.26.24 or later, or Arc agent 1.10.0 or later, is required.

Custom machine configuration policy definitions using AuditIfNotExists as well as DeployIfNotExists are in Generally Available (GA) support status.

How machine configuration manages remediation (Set)

Machine configuration uses the policy effect DeployIfNotExists for definitions that deliver changes inside machines. Set the properties of a policy assignment to control how evaluation delivers configurations automatically or on-demand.

A video walk-through of this document is available.

Machine configuration assignment types

There are three available assignment types when guest assignments are created. The property is available as a parameter of machine configuration definitions that support DeployIfNotExists.

The assignmentType property property is case sensitive

Assignment type Behavior
Audit Report on the state of the machine, but don't make changes.
ApplyAndMonitor Applied to the machine once and then monitored for changes. If the configuration drifts and becomes NonCompliant, it isn't automatically corrected unless remediation is triggered.
ApplyAndAutoCorrect Applied to the machine. If it drifts, the local service inside the machine makes a correction at the next evaluation.

When a new policy assignment is assigned to an existing machine, a guest assignment is automatically created to audit the state of the configuration first. The audit gives you information you can use to decide which machines need remediation.

Remediation on-demand (ApplyAndMonitor)

By default, machine configuration assignments operate in a remediation on demand scenario. The configuration is applied and then allowed to drift out of compliance.

The compliance status of the guest assignment is Compliant unless either:

  • An error occurs while applying the configuration
  • If the machine is no longer in the desired state during the next evaluation

When either of those conditions are met, the agent reports the status as NonCompliant and doesn't automatically remediate.

To enable this behavior, set the assignmentType property of the machine configuration assignment to ApplyandMonitor. Each time the assignment is processed within the machine, the agent reports Compliant for each resource when the Test method returns $true or NonCompliant if the method returns $false.

Continuous remediation (autocorrect)

Machine configuration supports the concept of continuous remediation. If the machine drifts out of compliance for a configuration, the next time it's evaluated the configuration is corrected automatically. Unless an error occurs, the machine always reports status as Compliant for the configuration. There's no way to report when a drift was automatically corrected when using continuous remediation.

To enable this behavior, set the assignmentType property of the machine configuration assignment to ApplyandAutoCorrect. Each time the assignment is processed within the machine, the Set method runs automatically for each resource the Test method returns false.

Disable remediation

When the assignmentType property is set to Audit, the agent only performs an audit of the machine and doesn't try to remediate the configuration if it isn't compliant.

Disable remediation of custom content

You can override the assignment type property for custom content packages by adding a tag to the machine with name CustomGuestConfigurationSetPolicy and value disable. Adding the tag disables remediation for custom content packages only, not for built-in content provided by Microsoft.

Azure Policy enforcement

Azure Policy assignments include a required property Enforcement Mode that determines behavior for new and existing resources. Use this property to control whether configurations are automatically applied to machines.

By default, enforcement is set to Enabled. Azure Policy automatically applies the configuration when a new machine is deployed. It also applies the configuration when the properties of a machine in the scope of an Azure Policy assignment with a policy in the category Guest Configuration is updated. Update operations include actions that occur in Azure Resource Manager, like adding or changing a tag. Update operations also include changes for virtual machines like resizing or attaching a disk.

Leave enforcement enabled if the configuration should be remediated when changes occur to the machine resource in Azure. Changes happening inside the machine don't trigger automatic remediation as long as they don't change the machine resource in Azure Resource Manager.

If enforcement is set to Disabled, the configuration assignment audits the state of the machine until a remediation task changes the behavior. By default, machine configuration definitions update the assignmentType property from Audit to ApplyandMonitor so the configuration is applied one time and then it isn't applied again until a remediation is triggered.

Optional: Remediate all existing machines

If an Azure Policy assignment is created from the Azure portal, on the "Remediation" tab a checkbox labeled "Create a remediation task" is available. When the box is checked, after the policy assignment is created remediation tasks automatically correct any resources that evaluate to NonCompliant.

The effect of this setting for machine configuration is that you can deploy a configuration across many machines by assigning a policy. You don't also have to run the remediation task manually for machines that aren't compliant.

Manually trigger remediation outside of Azure Policy

You can orchestrate remediation outside of the Azure Policy experience by updating a guest assignment resource, even if the update doesn't make changes to the resource properties.

When a machine configuration assignment is created, the complianceStatus property is set to Pending. The machine configuration service requests a list of assignments every 5 minutes. If the machine configuration assignment's complianceStatus is Pending and its configurationMode is ApplyandMonitor or ApplyandAutoCorrect, the service in the machine applies the configuration.

After the configuration is applied, the configuration mode dictates whether the behavior is to only report on compliance status and allow drift or to automatically correct.

Understanding combinations of settings

~ Audit ApplyandMonitor ApplyandAutoCorrect
Enforcement Enabled Only reports status Configuration applied on VM Create and reapplied on Update but otherwise allowed to drift Configuration applied on VM Create, reapplied on Update, and corrected on next interval if drift occurs
Enforcement Disabled Only reports status Configuration applied but allowed to drift Configuration applied on VM Create or Update and corrected on next interval if drift occurs

Next steps