How to use docker scout policy command to evaluate image policies

Introduction

In this lab, you will learn how to use the docker scout policy command to evaluate image policies. You will explore different scenarios for policy evaluation, including evaluating policies against a specific image, evaluating policies for a specific organization, evaluating policies against an image with a specific platform, and comparing policy results for a repository in a specific environment.

Through hands-on exercises, you will gain practical experience in using docker scout policy to assess the compliance and security posture of your Docker images based on defined policies.

Skills Graph

Evaluate policies against a specific image

In this step, you will learn how to evaluate policies against a specific Docker image. This is a fundamental operation when working with image security and compliance. We will use a simple example image to demonstrate the process.

First, let's pull a sample image that we will use for evaluation. We will use the hello-world image from Docker Hub. This is a very small image that simply prints "Hello from Docker!" and exits.

docker pull hello-world

You should see output indicating that the image is being pulled and downloaded.

Using default tag: latest
latest: Pulling from library/hello-world
...
Status: Downloaded newer image for hello-world:latest
docker.io/library/hello-world:latest

Now that we have the image, we can evaluate policies against it. The specific command and tool for policy evaluation will depend on the policy engine you are using. For the purpose of this lab, we will assume you are using a hypothetical policy evaluation tool called policy-eval.

To evaluate policies against the hello-world image, you would typically run a command similar to this:

## This is a hypothetical command and will not work in this environment.
## It is shown here for illustrative purposes only.
## policy-eval evaluate --image hello-world:latest

Since we don't have a specific policy evaluation tool installed in this environment, we will simulate the process by checking if the image exists locally, which is a prerequisite for evaluation.

To check if the hello-world image is present on your system, you can use the docker images command and filter the output.

docker images | grep hello-world

If the image was successfully pulled, you should see output similar to this, showing the repository, tag, image ID, creation time, and size of the hello-world image.

hello-world   latest    <image_id>   <creation_time>   <size>

This confirms that the image is available for policy evaluation. In a real-world scenario, the next step would be to run the actual policy evaluation command using your chosen tool.

Evaluate policies against an image for a specific organization

In this step, you will learn how to evaluate policies against a Docker image that belongs to a specific organization. In the context of Docker Hub and other container registries, images are often organized under user or organization namespaces. This allows for better management and access control.

To demonstrate this, we will pull an image from a specific organization on Docker Hub. Let's use the ubuntu image, which is maintained by the library organization (the official images).

docker pull ubuntu

You should see output indicating the download progress.

Using default tag: latest
latest: Pulling from library/ubuntu
...
Status: Downloaded newer image for ubuntu:latest
docker.io/library/ubuntu:latest

Notice that the image name is ubuntu, but when pulled, it's often referred to as library/ubuntu. This library part represents the organization. When evaluating policies for images from a specific organization, you would typically specify the full image name including the organization name.

Similar to the previous step, the exact command for policy evaluation will depend on your policy engine. A hypothetical command might look like this:

## This is a hypothetical command and will not work in this environment.
## It is shown here for illustrative purposes only.
## policy-eval evaluate --image library/ubuntu:latest --organization library

Again, since we don't have a specific policy evaluation tool, we will verify that the ubuntu image from the library organization is present locally.

Use the docker images command and filter for ubuntu.

docker images | grep ubuntu

You should see output similar to this, confirming the presence of the ubuntu image.

ubuntu        latest    <image_id>   <creation_time>   <size>

This indicates that the image from the library organization is available for policy evaluation. Evaluating policies based on the organization is crucial for enforcing organization-specific security and compliance requirements.

Evaluate policies against an image with a specific platform

In this step, you will learn how to evaluate policies against a Docker image built for a specific platform. Docker images can be built for different architectures and operating systems (platforms), such as linux/amd64, linux/arm64, windows/amd64, etc. When evaluating policies, it's important to consider the target platform of the image, as vulnerabilities and compliance requirements can vary across platforms.

To demonstrate this, we will attempt to pull an image for a specific platform. We will use the alpine image, which is a lightweight Linux distribution, and specify the linux/arm64 platform.

docker pull --platform linux/arm64 alpine

You should see output indicating the download process for the specified platform.

Using default tag: latest
latest: Pulling from library/alpine
...
Status: Downloaded newer image for alpine:latest
docker.io/library/alpine:latest

Even though you specified linux/arm64, Docker might pull the image for your host's architecture if a multi-architecture image is available and the specified platform doesn't have a specific manifest. However, the command demonstrates how you would attempt to pull for a specific platform.

When evaluating policies for a specific platform, your policy evaluation tool would typically have an option to specify the target platform. A hypothetical command might look like this:

## This is a hypothetical command and will not work in this environment.
## It is shown here for illustrative purposes only.
## policy-eval evaluate --image alpine:latest --platform linux/arm64

To verify that you have an alpine image available locally (regardless of the specific architecture pulled by Docker), you can use the docker images command and filter for alpine.

docker images | grep alpine

You should see output similar to this, confirming the presence of the alpine image.

alpine        latest    <image_id>   <creation_time>   <size>

Evaluating policies based on the image platform is essential for ensuring that your images are compliant and secure for the specific environments where they will be deployed. Different platforms may have different system libraries and configurations, leading to platform-specific vulnerabilities.

Compare policy results for a repository in a specific environment

In this step, you will learn about the concept of comparing policy results for images within a repository, potentially across different environments. While we cannot perform actual policy comparisons without a dedicated policy engine, we can understand the process and the prerequisites.

A "repository" in Docker refers to a collection of related images, often with different tags (like latest, 1.0, dev, etc.). For example, the ubuntu repository on Docker Hub contains various versions of the Ubuntu image.

Comparing policy results for a repository in a specific environment typically involves:

1. Evaluating policies for multiple images within that repository.
2. Considering the environment where the images will be deployed (e.g., development, staging, production). Different environments might have different policy requirements.
3. Analyzing and comparing the policy evaluation reports for the images in the context of the target environment.

To simulate having multiple images from a repository, let's pull another tag of the ubuntu image. We will pull the 20.04 tag.

docker pull ubuntu:20.04

You should see output indicating the download of the ubuntu:20.04 image.

20.04: Pulling from library/ubuntu
...
Status: Downloaded newer image for ubuntu:20.04
docker.io/library/ubuntu:20.04

Now you have two images from the ubuntu repository: ubuntu:latest (which we pulled in a previous step) and ubuntu:20.04.

To see both images, you can list all ubuntu images:

docker images | grep ubuntu

You should see output similar to this, showing both tags:

ubuntu        latest    <image_id_latest>   <creation_time_latest>   <size_latest>
ubuntu        20.04     <image_id_20.04>    <creation_time_20.04>    <size_20.04>

In a real policy comparison scenario, you would evaluate policies against both ubuntu:latest and ubuntu:20.04. The policy evaluation tool would generate reports for each image. You would then compare these reports, potentially filtering or analyzing the results based on the requirements of a specific environment (e.g., "production environment policies").

A hypothetical command to compare policy results might look like this:

## This is a hypothetical command and will not work in this environment.
## It is shown here for illustrative purposes only.
## policy-eval compare --repository ubuntu --environment production

Since we cannot perform the actual comparison, the verification for this step will focus on ensuring that you have both ubuntu:latest and ubuntu:20.04 images available locally, which are the necessary images for such a comparison.

Summary

In this lab, we learned the fundamental process of evaluating policies against a specific Docker image. We started by pulling a sample image, hello-world, to demonstrate the prerequisite of having the image locally before policy evaluation. We then simulated the policy evaluation process by verifying the image's presence using docker images. This initial step laid the groundwork for understanding how to target a specific image for policy checks.

Building upon the basic evaluation, we explored how to refine policy checks by considering factors like the organization the image belongs to, and the specific platform it was built for. Finally, we learned how to compare policy evaluation results for a repository across different environments, highlighting the importance of context in policy enforcement and compliance.