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Deploying OPA on Azure Container Apps

Azure Container Apps provides a fully managed platform for deploying and scaling containerized applications. It is well-suited for running off-the-shelf software, such as OPA, handling scaling, networking, and infrastructure, allowing you to focus on developing your applications.

This guide details the steps and considerations when deploying OPA as a Policy Decision Point (PDP) on Azure Container Apps.

Selecting a Container Image​

It is recommended to use the openpolicyagent/opa:<version> variant available on Docker Hub. Users without access to Docker Hub may need to mirror these images to a Azure Container Registry.

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Note: Avoid using the latest tag in production environments.

Ingress, Authentication & Authorization Considerations​

In Azure Container Apps, endpoints can be public or private to only Container Apps. Since OPA typically handles requests from internal services (PEPs), setting up a private endpoint is advisable where possible. For public endpoints, use additional authentication mechanisms if Azure AD cannot be used.

While OPA’s primary role is providing authorization decisions as a PDP, OPA itself should restrict access to ensure that only authorized PEPs can interact with it.

If PEP applications are authenticated using Azure AD, their tokens can identify them to OPA. Otherwise, consider using client certificates or tokens. Refer to the OPA documentation for more information on securing OPA with tokens or certificates.

CPU Scaling & Memory Allocation​

OPA is lightweight, but to achieve low-latency responses in serverless environments, it is recommended to configure Azure Container Apps with a minimum of 1 OPA instance, using 1 vCPU and 2GB of memory.

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By default, Container Apps can scale to 0 instances, which may cause latency issues for PEPs if not OPAs are running to serve requests.

Increase memory allocation if substantial data needs to be loaded into OPA for policy evaluations. Test deployments with realistic data and traffic to ensure satisfactory production performance.

Creating the OPA App​

To deploy OPA to Container Apps, specify these settings in the initial revision t create the app. In a later step, we'll create the secret for the OPA configuration file and mount it into the container.

Throughout the following steps, we'll be using these values for the OPA Container App. Replace the values with the details from your environment before continuing to have the values set in the steps below.

The first step is to create a new Container App. Use these values below to create the app and the first revision:

  • Container app name: e.g. opa or some name in line with internal naming standards.

  • Region: Choose the region where your PEP applications are hosted.

  • Image source: Docker Hub or OPA image replicated to private registry.

  • Container Image URL: Valid versions: e.g. X.Y.Z not latest or vX.Y.Z. Review the OPA images for a list of available versions.

  • Use the argument override to run the server, and load the configuration file (note the commas):

    run, --server, --addr=:8181, --config-file=/run/secrets/opa-config.yaml

  • Ingress: OPA will be listening on port 8181, use this as the 'Target Port' when enabling ingress. Session affinity is not required.

  • For 'Container resource allocation', use 1 vCPU and 2GB of memory.

Once created, the app will be deployed with the specified image. In the next step we'll create an link the OPA configuration file as a secret mount.

Loading OPA Configuration​

OPA requires a configuration file specifying policy bundle locations. For secure management, store the OPA configuration file as a secret in Azure Container Apps. To define a secret, follow the steps in the Azure documentation, or refer to the CLI example below.

To download the OPA configuration file from Styra DAS, use these parameters:

curl --silent \
  -H "Authorization: Bearer " \
  -o opa-conf.yaml \
  "/v1/systems//assets/opa-config"

Once you have the opa-conf.yaml file locally, we can create a new revision referencing this secret.

Create a new revision and add a volume called secrets. Mount opa-confif at opa-config.yaml. Then, select the OPA container and add a mount for secrets at /run/secrets. This measn the OPA configuration file will be available at /run/secrets/opa-config.yaml within the container, as specified in the container definition above.

Further Reading​

  • SDKs for building PEP applications in your language of choice.