Stack Policy and Resource Policies - Tutorial

Welcome to this tutorial on stack policy and resource policies in AWS CloudFormation. Stack policies and resource policies provide fine-grained control over the permissions and access control for your CloudFormation stacks and resources. Understanding how to use these policies effectively is essential for maintaining the security and integrity of your infrastructure.

Example of a Stack Policy

Let's consider an example where you have a CloudFormation stack that contains sensitive resources. To prevent accidental deletion of these resources, you can define a stack policy to restrict modifications.


    {
      "Statement" : [
        {
          "Effect" : "Deny",
          "Action" : "Update:*",
          "Principal" : "*",
          "Resource" : "*"
        }
      ]
    }

In the above example, the stack policy denies any updates to the stack, effectively preventing modifications to the resources within it.

Steps to Implement Stack Policy and Resource Policies

Understand the concepts and purpose of stack policies and resource policies.
Identify the resources or stacks for which you want to define policies.
Choose the appropriate type of policy: stack policy or resource policy.
Write or define the policy using the JSON or YAML syntax.
Attach the policy to the stack or the specific resource.
Test the policy to ensure it functions as intended.

Common Mistakes with Stack Policy and Resource Policies

Using overly permissive policies that grant excessive permissions.
Forgetting to update the policies when making changes to resources or stacks.
Not testing the policies thoroughly before deploying them.
Ignoring warnings or errors related to policy evaluations.
Not regularly reviewing and updating the policies as requirements change.

Frequently Asked Questions (FAQs)

1. What is the difference between stack policy and resource policies?

A stack policy is applied to the entire CloudFormation stack and can control actions such as stack updates and deletions. Resource policies, on the other hand, are attached to specific resources within a stack and control actions specific to those resources.

2. Can I override a stack policy with a resource policy?

No, a stack policy takes precedence over a resource policy. If a stack policy denies an action, a resource policy cannot allow it.

3. How can I test the effects of a stack policy before applying it?

You can use the aws cloudformation validate-stack-policy command to validate a stack policy without actually applying it to a stack.

4. Can I use IAM policies for access control within CloudFormation?

Yes, you can use IAM policies to control access to CloudFormation operations, but they are separate from stack policies and resource policies.

5. Are there any limits to the size or complexity of stack policies or resource policies?

Yes, there are limits to the size and complexity of policies. For example, stack policies have a maximum size limit of 16 KB, and resource policies must be less than 64 KB.

Summary

Stack policies and resource policies in AWS CloudFormation offer powerful control mechanisms for managing access and permissions within your infrastructure. By understanding how to define and implement these policies, you can ensure the security and integrity of your CloudFormation stacks and resources.