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Implementing policy as code with Open Policy Agent

In this post, I will show you how to implement policy as code with Open Policy Agent (OPA) and Azure.

What is Open Policy Agent?

Open Policy Agent (OPA) is an open-source, general-purpose policy engine that enables you to define and enforce policies across your cloud-native stack. OPA provides a high-level declarative language called Rego that you can use to write policies that are easy to understand and maintain.

Why use Open Policy Agent?

There are several reasons to use OPA:

  • Consistency: OPA allows you to define policies in a single place and enforce them consistently across your cloud-native stack.
  • Flexibility: OPA provides a flexible policy language that allows you to define policies that are tailored to your specific requirements.
  • Auditability: OPA provides a transparent and auditable way to enforce policies, making it easy to understand why a policy decision was made.
  • Integration: OPA integrates with a wide range of cloud-native tools and platforms, making it easy to enforce policies across your entire stack.

Getting started with Open Policy Agent

To get started with OPA, you need to install the OPA CLI and write some policies in Rego.

You can install the OPA CLI by downloading the binary from the OPA GitHub releases page, you can check the installation guide for more details.

Once you have installed the OPA CLI, you can write policies in Rego. Rego is a high-level declarative language that allows you to define policies in a clear and concise way.

Here's a simple example of a policy that enforces a naming convention for Azure resources:

package azure.resources

default allow = false

allow {
    input.resource.type == "Microsoft.Compute/virtualMachines"
    input.resource.name == "my-vm"
}

This policy allows resources of type Microsoft.Compute/virtualMachines with the name my-vm. You can write more complex policies that enforce a wide range of requirements, such as resource tagging, network security, and access control.

Integrating Open Policy Agent with Azure

To integrate OPA with Azure, you can use the Azure Policy service, which allows you to define and enforce policies across your Azure resources. You can use OPA to define custom policies that are not supported by Azure Policy out of the box, or to enforce policies across multiple cloud providers.

Conclusion

Open Policy Agent is a powerful tool that allows you to define and enforce policies across your cloud-native stack. By using OPA, you can ensure that your infrastructure is secure, compliant, and consistent, and that your policies are easy to understand and maintain. I hope this post has given you a good introduction to OPA and how you can use it to implement policy as code in your cloud-native environment.

Additional resources

I have created a GitHub repository with some examples of policies written in Rego that you can use as a starting point for your own policies.

References