Outputs for cross-stack references in AWS - Mini Project: Build & Apply

Outputs for cross-stack references

📖 Scenario: You are working on an AWS CloudFormation project where you want to share information between two stacks. For example, one stack creates a VPC and outputs its ID. Another stack needs to use that VPC ID to create resources inside it.

🎯 Goal: Build two CloudFormation stacks where the first stack outputs a value, and the second stack imports that output using cross-stack references.

📋 What You'll Learn

Create a CloudFormation stack named NetworkStack that defines a VPC resource with a specific CIDR block.

Add an output in NetworkStack that exports the VPC ID with the export name MyVPCID.

Create a second CloudFormation stack named ComputeStack that imports the VPC ID using the export name MyVPCID.

Use the imported VPC ID to define a subnet resource inside ComputeStack.

💡 Why This Matters

🌍 Real World

Sharing resource IDs or configuration values between different CloudFormation stacks is common in real AWS projects to keep infrastructure modular and reusable.

💼 Career

Understanding cross-stack references is essential for cloud engineers and architects to design scalable and maintainable AWS infrastructure.

1

Create the NetworkStack with a VPC resource

Create a CloudFormation template for NetworkStack that defines a VPC resource named MyVPC with the CIDR block 10.0.0.0/16.

AWS

# Define a VPC resource named MyVPC with CIDR block 10.0.0.0/16
# Your code here

Need a hint?

Use the AWS::EC2::VPC resource type and set CidrBlock to 10.0.0.0/16.

2

Add an output exporting the VPC ID

Add an Outputs section to NetworkStack that exports the VPC ID of MyVPC with the export name MyVPCID. Use the intrinsic function !Ref MyVPC for the output value.

AWS

Resources:
  MyVPC:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: 10.0.0.0/16

# Add Outputs section exporting MyVPC ID
# Your code here

Need a hint?

Use Outputs with a name like VPCID. Set Value to !Ref MyVPC and add an Export with Name: MyVPCID.

3

Create ComputeStack importing the VPC ID

Create a CloudFormation template for ComputeStack that imports the VPC ID using the intrinsic function !ImportValue MyVPCID and assigns it to a parameter named ImportedVPCID.

AWS

# Define a parameter ImportedVPCID that imports the value MyVPCID
# Your code here

Need a hint?

Use a Parameters section with ImportedVPCID of type String. Set Default to !ImportValue MyVPCID.

4

Define a subnet in ComputeStack using the imported VPC ID

Add a subnet resource named MySubnet in ComputeStack that uses the imported VPC ID from the parameter ImportedVPCID as its VpcId. Set the subnet's CIDR block to 10.0.1.0/24.

AWS

Parameters:
  ImportedVPCID:
    Type: String
    Description: Imported VPC ID
    Default: !ImportValue MyVPCID

# Add a subnet resource MySubnet using ImportedVPCID
# Your code here

Need a hint?

Define a AWS::EC2::Subnet resource named MySubnet. Use !Ref ImportedVPCID for VpcId and set CidrBlock to 10.0.1.0/24.