By UATeam in AWS —

AWS CloudFormation Nested Stack Example: A Comprehensive Guide

AWS CloudFormation is a powerful infrastructure-as-code (IaC) service that simplifies resource provisioning and management. Nested stacks, a feature of CloudFormation, enable modularization by allowing you to reuse templates within other CloudFormation stacks. This article provides a practical example of using AWS CloudFormation nested stacks to streamline resource management.

What Are CloudFormation Nested Stacks?

Nested stacks allow you to:

  • Reuse CloudFormation templates by embedding them as resources in parent stacks.
  • Simplify large and complex templates by breaking them into manageable components.
  • Improve maintainability and modularity by separating different resource groups.

AWS CloudFormation Nested Stack Example

Objective

We’ll create a parent stack that includes nested stacks for:

  1. A VPC (Virtual Private Cloud).
  2. An S3 bucket.
  3. An EC2 instance.

Step 1: Create Nested Stack Templates

1. VPC Template

Save the following as vpc-template.yaml:

Resources:
  VPC:
    Type: "AWS::EC2::VPC"
    Properties:
      CidrBlock: "10.0.0.0/16"
      EnableDnsSupport: true
      EnableDnsHostnames: true
      Tags:
        - Key: Name
          Value: ExampleVPC

2. S3 Bucket Template

Save the following as s3-template.yaml:

Resources:
  S3Bucket:
    Type: "AWS::S3::Bucket"
    Properties:
      BucketName: "example-nested-stack-bucket"

3. EC2 Instance Template

Save the following as ec2-template.yaml:

Resources:
  EC2Instance:
    Type: "AWS::EC2::Instance"
    Properties:
      InstanceType: "t2.micro"
      ImageId: "ami-0c94855ba95c71c99" # Replace with an appropriate AMI ID for your region
      KeyName: "example-keypair" # Ensure you have created this key pair in your region

Step 2: Create the Parent Template

Save the following as parent-template.yaml:

Resources:
  VPCStack:
    Type: "AWS::CloudFormation::Stack"
    Properties:
      TemplateURL: "https://your-s3-bucket/vpc-template.yaml"

  S3Stack:
    Type: "AWS::CloudFormation::Stack"
    Properties:
      TemplateURL: "https://your-s3-bucket/s3-template.yaml"

  EC2Stack:
    Type: "AWS::CloudFormation::Stack"
    Properties:
      TemplateURL: "https://your-s3-bucket/ec2-template.yaml"

Step 3: Upload Templates to S3

  1. Upload the vpc-template.yaml, s3-template.yaml, and ec2-template.yaml files to an S3 bucket.
  2. Make note of the S3 URLs for these templates.

Step 4: Deploy the Parent Stack

  1. Navigate to the CloudFormation Console.
  2. Click Create Stack → With New Resources (Standard).
  3. Upload the parent-template.yaml file or provide its S3 URL.
  4. Follow the prompts and create the stack.

Step 5: Verify Resources

  1. CloudFormation Console:
    • Check the status of the parent stack and nested stacks to ensure they are created successfully.
  2. AWS Management Console:
    • VPC: Verify the creation of the VPC under the VPC Console.
    • S3 Bucket: Check the S3 bucket in the S3 Console.
    • EC2 Instance: Confirm the EC2 instance is running in the EC2 Console.

Advantages of Nested Stacks

  1. Modularity:
    • Break large templates into reusable components for better organization.
  2. Simplified Maintenance:
    • Update nested stacks independently without modifying the parent stack.
  3. Improved Collaboration:
    • Different teams can manage nested stacks separately while contributing to the same infrastructure.

Best Practices for Using Nested Stacks

  1. Version Control Templates: Store templates in a version control system like Git for easy tracking and updates.
  2. Parameter Passing: Use parameters to pass values from the parent stack to nested stacks for greater flexibility.
  3. Keep Nested Templates Simple: Avoid overloading nested templates with excessive resources.
  4. Test Independently: Test each nested stack individually before integrating them into the parent stack.

Conclusion

AWS CloudFormation nested stacks are an excellent way to manage complex infrastructures by promoting modularity and reusability. In this example, we demonstrated how to create a parent stack that incorporates nested stacks for a VPC, an S3 bucket, and an EC2 instance. By leveraging nested stacks, you can simplify infrastructure management, improve maintainability, and streamline resource deployment in AWS.