Walkthrough using Azure Policy to audit and enforce compliance

azpolicyUse Azure Policy to manage and enforce your standards for governance and compliance and to assess that compliance at scale. When you implement Azure Policy, you are effectively adding guard-rails for your users. But you also have a way to audit your organization compliance against a particular policy.

In this walkthrough, you will learn the implications of using a Policy in Azure. For this walkthrough, you will use Azure CLI to create a storage account that will not be compliant, but allowing its contents to be accessed using HTTP. Then you will add a Policy that requires HTTPS, and see how you can audit existing, non-compliant resource. You will audit the resource using the portal and using PowerShell script. Then you will create another non-compliant resource and see how Azure blocks the resource during creation.

Prerequisites

  • It is helpful that you understand resource groups and about storage accounts. Although the sample provides code, you will want to know how to upload a small file into Azure blob storage. You can use the portal or AzCopy.
  • The sample shows how to use specific role, but you should understand about role based access control roles.
  • You will need owner or contributor access in your subscription.

Definitions

First let’s start with some definitions:

Business rule is a standard that the business wants to audit or wants to insure is compliance. Often, but not always, business rules follow compliance standards, such as ISO 27001 or NIST.

Resource Provider is service that supplies Azure resources. For example, a common resource provider is Microsoft.Storage, which supplies the storage resource. The name of a resource type is in the format: {resource-provider}/{resource-type}.

Resource is a manageable item that is available through Azure. Virtual machines, storage accounts, web apps, databases, and virtual networks are examples of resources. when the resource is created, it has an id. The id has a field that has a format like /subscriptions//resourceGroups//providers/Microsoft.Compute/disks/.

Resources have properties that you set when you create the resource. For example, when you create a storage account, you set its location.

Azure Policy examines properties on resources that are represented in Resource Manager and properties of some Resource Providers. For example the location of a resource is a property that a policy can audit.

Policy definition is the JSON implementation of a business rule.

Several business rules can be grouped together into a Policy initiative.

The policy definition or initiative is assigned to any scope that can be a management groups, subscriptions, resource groups, or individual resources.

A policy assignment applies the policy to all resources within the scope. For example, if the policy

For more information, see:

Identify the business requirements

Let’s begin by defining the compliance requirements.

The requirements should clearly identify both the “to be” and the “not to be” resource states.

For example in this case:

Compliance Standard ISO 27001
Control A.10.1.1 Policy on the use of cryptographic controls
Requirement ISO requirement: Audit secure transfer to storage accounts
Our business requirement: Require secure transfer to storage accounts
Rules
  • Each storage account must be enabled for HTTPS
  • Each storage account must be disabled for HTTP

First, let’s figure out the resource property that we want to build our policy on.

Explore resource properties that might want to check

Each resource in Azure is built on a set of APIs that are defined at the top level as Azure resource providers. A resource provider is [uhm] a service that provides resources, such as storage.

For the list of the providers, see Resource providers for Azure services. To get a list of providers and the status of whether they are installed in your subscription, use the following command:

Let’s start by reviewing the Microsoft.Storage resource provider. Resource Manager template reference for the storage account resource gives you a (nearly all) the property. In this case, the supportsHttpsTrafficOnly will be the one we use.

supportshttps

In the StorageAccountPropertiesCreateParameters object is the supportsHttpsTrafficOnly.

httpstraffic

Another way to explore resources

Once you have created a resource, you can inspect their properties. Use the Azure Resource Explorer to inspect the context of your subscription. You can browse by providers, subscriptions, resource groups, and resources.

Find the property alias

We need to map the property we found to it’s alias. When you create a policy, it uses aliases to restrict what values or conditions are allowed. Each alias maps to paths in different API versions for a given resource type. During policy evaluation, the policy engine gets the property path for that API version.

Use the following cli to get the alias used by the Azure Policy.

As shown in the following illustration, the results show that supportsHttpsTrafficOnly is supported.

supporthttps

This means we can write a policy based on supportsHttpsTrafficOnly.

Another way to query the aliases is to use Azure Graph. The following code installs Azure Graph into the CLI and queries the aliases. The results are provided in a heirarchy that may be easier to view.

Before we go install a custom policy, let’s create a sample resource that will not be compliant.

Create a non-compliant storage account

Let’s begin by creating a storage account resource that allows applications to access the storage, create a container, and upload a file. Log into Azure using az login, then use the following code to create a resource group, storage account, and storage container; grant yourself contributor access to the storage account, create a file and upload it.

Note: For the demo to work, you will explicitly need to assign the Storage Blob Data Contributor role to yourself. Even though you are the account owner, you need explicit permissions to perform data operations against the storage account.

The storage account is intentionally created with --https-only false.

Next, before we create our custom policy, let’s test to see if there is a voilation of Azure policy from our existing policies.

Test against current policies

Does the new storage resource already violate one of our policies? Log into the Azure Portal, search in the search bar for Policy. And there is an intiative that was installed by Azure Security Center that flags the storage resource as not being compliant, as shown in the following illustration.

notcompliant

Click through the links initiative and you can see resource that we just created and the rule that was violated, as shown in the following illustration.

resourcecompliance

Our business requirement is to now allow the creation of storage accounts, not to just audit. In the next step, create a custom policy to stop anyone from creating a storage account that is non-compliant.

Create custom policy to deny the non-compliant storage creation

It is possible to go into the portal and just change the policy. You could go into the initiative, edit the assignment of the policy, and change the parameter from Audit to Deny. But in our world where you want to track the changes and to automate your new initiatives, you will want to create a custom policy that denies creation of the non-compliant resource.

The following JSON (from the Microsoft documentation Tutorial: Create a custom policy definition) shows the policy.

Several itesm to note from the code:

  • The displayName and description elements show the intent of the policy.
  • The effectType element on lines 7 to 18 defaults to Deny, but allows you to set the effect to Disabled, which allows you to turn off the rule.
  • The policyRule requies both:
    • The storage account type is Microsoft.Storage/storageAccounts and
    • The storage account supportsHttpsTrafficOnly property is not true

Next, let’s split up our policy so we can create the policy definition.

Create the policy definition

The policy definition consists of rules and parameters for those rules. Both are declared in JSON. The following script uses Bash to create two files, one for the rules and one to define the parameters.

Use az policy definition create to create the policy definition. See Create a policy definition with Azure CLI. The following code creates a policy definition and saves the policy definition to a subscription. It does not assign the policy to the subscription.

Once you have defined the policy, you can find it in the portal. Open the portal, search Policy, click Definitions to all the the policies. Search on https. The following illustration shows the definition of the matchint policies.

denystorage

Click Deny storage accounts not using only HTTPS to see your policy definition.

You may want to consider the following best practices:

You could have saved the policy to a management group, which is then available as a the policy definition to all of the subscriptions associated with the management group.

The rule and param URLs can point to your rules in GitHub or Azure DevOps.

Now that we have a definition available in our subsription, you need to apply it.

Apply the policy to a scope

Now that your policy has been defined and available in your subscription, you need to assign the policy. This step sets the policy to a particular scope.

Valid scopes are management group, subscription, resource group, and resource as shown in this table:

Management group /providers/Microsoft.Management/managementGroups/MyManagementGroup
Subscription /subscriptions/c2b15f36-f522-451c-84e3-a4fc54056617
Resource group /subscriptions/c2b15f36-f522-451c-84e3-a4fc54056617/resourceGroups/myGroup
Resource /subscriptions/c2b15f36-f522-451c-84e3-a4fc54056617/resourceGroups/myGroup/providers/Microsoft.Compute/virtualMachines/myVM

You can assign the policy in the portal. See

To automate it, use an Azure CLI script command az policy assignment create to assign the policy definition to the scope. The following sample assigns the policy to the subscription scope.

As it assigns the policy, it also provides the parameters for this particular assignment.

Now that you have the policy assigned, what happened to the non-compliant resource?

Check compliance

Once you have assigned the policy to your subscription, you will want to check compliance. The resource created in an earlier step still fails based on the Security Center rule. But it also fails based on the new custom rules you added in the previous step.

To view, open Policy blade in the Azure portal. Click Compliance.

policycompliance

It takes a few minutes to scan your resources.

Assigning a policy with a “deny” effect may take up to 30 mins (average case) and 1 hour (worst case) to start denying the creation of non-compliant resources.

You can query for non-compliant resources in PowerShell. The following cmdlet returns the details for all non-compliant storage accounts.

Creation of a non-compliant resource now fails

To test that the policy denies creation of an non-compliant resource, run the script in the previous section to create a non-compliant storage account. The following code tries to create a new storage account in the same resource group.

Once completed, you will see an error message.

policyerror

When you go into the portal, click Compliance in the Policy page to see results. Click Require https for storage in subscription to see the summary of non-compliance. Notice that the existing resource is audited as not compliant. And the denial for the creating of the non-compliant storage account is shown.

policycompliance2

View compliance in Log Analytics

Because you installed a Log Analytics workspace as described in the post Setting up Log Analytics workspace for production in enterprise, you can view AzureActivity from the Activity Log Analytics solution tied to your subscription.

policyactivitylog

Apply policy using a ARM template

The documentation Quickstart: Create a policy assignment to identify non-compliant resources by using a Resource Manager template shows how you can deploy a policy to a resource group.

You will need the policyDefinitionID. Use the following command to get the properties of the policy you want to apply.

Use the properties when you deploy the ARM template.

Summary

This was a deep-dive walkthrough into how to define and implement your own policies, which build-in governance best practices for your users. You learned the workflow of a custom policy and how to deploy the policy into either a subscription or management group. And you learned how to check your compliance with all your initiatives.

Next steps

Resources


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