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Enforcing code ownership#

With PSRule, you can layer on custom rules with to implement organization specific requirements. These custom rules work side-by-side with PSRule for Azure.

Pull requests are a key concept within common Git workflows used with DevOps to enforce peer review. To support peer review across a team tools such as GitHub and Azure DevOps provide code ownership. Code ownership, allows mix discipline teams to direct peer reviews based the path of a changed file.

For sensitive changes such as firewall or policy exemptions, peer reviews may form a security control. In these cases, it may be important that specific paths are used for Infrastructure as Code artifacts.

Info

Code ownership is implemented through CODEOWNERS in GitHub and required reviewers in Azure Repos.

Abstract

The following scenario shows how to create a custom rule to validate the path of artifacts. The scenario walks you through the process so that you can apply the same concepts for similar requirements.

Creating a new rule#

Within the .ps-rule sub-directory create a new file called Org.Azure.Rule.ps1. Use the following snippet to populate the rule file:

# Synopsis: Policy exemptions must be stored under designated paths for review.
Rule 'Org.Azure.Policy.Path' -Type 'Microsoft.Authorization/policyExemptions' {
    $Assert.WithinPath($PSRule.Source['Parameter'], '.', @(
        'deployments/policy/'
    ));
}

Some key points to call out with the rule snippet include:

  • The name of the rule is Org.Azure.Policy.Path. Each rule name must be unique.
  • The rule applies to resources with the type of Microsoft.Authorization/policyExemptions. i.e. Policy exemptions.
  • The synopsis comment above the rule is read and used as the default recommendation if the rule fails. The rule recommendation appears in output and is intended as an instruction to remediate the failure.
  • The assertion $Assert.WithinPath ensures the specifies path is within the deployments/policy/ sub-directory.
  • The automatic variable $PSRule.Source exposes the source path for the resource. PSRule for Azure exposes a Template and Parameter source for resources originating from a template.

Tip

For recommendations on naming and storing rules see storing custom rules.

Binding type#

Rules packaged within PSRule for Azure will automatically detect Policy Exemptions by their type properties. Standalone rules will get their type binding configuration from ps-rule.yaml instead.

To configure type binding:

  • Create/ update the ps-rule.yaml file within the root of the repository.
  • Add the following configuration snippet.
# Configure binding options
binding:
  targetType:
  - 'resourceType'
  - 'type'

Some key points to call out include:

  • Configuring the binding for targetType allows rules to use the -Type parameter. Our custom rule uses -Type 'Microsoft.Authorization/policyExemptions'.
  • The binding configuration will use the resourceType property if it exists, alternative it will use type. If neither property exists, PSRule will use the object type.

Testing locally#

To test the custom rule within Visual Studio Code, see validating locally. Alternatively you can test the rule manually by running the following from a PowerShell terminal.

Assert-PSRule -Path '.ps-rule/' -Module 'PSRule.Rules.Azure' -InputPath . -Format File

Sample code#

Grab the full sample code for each of these files from:

Last update: 2021-11-20

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