Nested Stacks in AWS CloudFormation - krdheeraj51/aws-labs GitHub Wiki

In AWS CloudFormation, a nested stack is essentially a CloudFormation stack that is created and managed as part of another CloudFormation stack. Think of it like embedding a stack within a stack.

Why Use Nested Stacks?

  • Modularity and Organization: When your infrastructure grows, your CloudFormation templates can become very large and complex. Nested stacks allow you to break down your infrastructure into smaller, more manageable units. Each nested stack can represent a specific component of your architecture (e.g., a VPC, a database, an application server).
  • Reusability: You can reuse the same nested stack across multiple parent stacks. This is particularly beneficial when you have common infrastructure patterns that are used in different parts of your environment. For example, you might have a standard VPC configuration that you want to use for all your applications.
  • Encapsulation: Nested stacks encapsulate resources and configurations within a clear boundary. This helps prevent naming conflicts and makes it easier to manage dependencies between different parts of your infrastructure.
  • Simplified Updates: You can update individual nested stacks without affecting the entire infrastructure. This makes it easier to deploy changes and reduces the risk of unintended consequences.

How Nested Stacks Work

  1. Parent Stack: The parent stack is the main CloudFormation template that defines the overall infrastructure. It includes a resource of type AWS::CloudFormation::Stack for each nested stack.
  2. Nested Stack: Each nested stack is a separate CloudFormation template that defines a specific part of your infrastructure.
  3. TemplateURL: In the parent stack, you specify the TemplateURL property for each nested stack. This property points to the location of the nested stack template (usually an S3 bucket).
  4. Parameters: You can pass parameters to nested stacks from the parent stack. This allows you to customize the configuration of the nested stacks.
  5. Outputs: Nested stacks can have outputs that can be used by the parent stack or other nested stacks. This allows you to create dependencies between different parts of your infrastructure.

Example

Imagine you're building a web application. You might have:

  • Parent Stack: This stack creates the overall environment, including a VPC, subnets, and security groups.
  • Nested Stack 1: This stack creates the web servers.
  • Nested Stack 2: This stack creates the database.

The parent stack would include resources of type AWS::CloudFormation::Stack for the web server stack and the database stack. It would also pass parameters to these stacks, such as the instance type for the web servers and the database instance size.

Benefits of Using Nested Stacks

  • Improved organization and maintainability of your CloudFormation templates.
  • Increased reusability of infrastructure components.
  • Simplified updates and deployments.
  • Reduced risk of errors and unintended consequences.

If you're working with complex infrastructure in AWS, nested stacks are a valuable tool for managing your CloudFormation templates and simplifying your deployments.