AWS Cloudformation

AWS CloudFormation Skill

Create and manage infrastructure as code with CloudFormation.

Quick Reference

Parameters

Required

Optional

Template Structure

AWSTemplateFormatVersion: '2010-09-09'
Description: 'Production VPC with 3-tier architecture'

Parameters:
  Environment:
    Type: String
    AllowedValues: [dev, staging, prod]

Mappings:
  RegionMap:
    us-east-1:
      AMI: ami-12345678

Conditions:
  IsProd: !Equals [!Ref Environment, prod]

Resources:
  VPC:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: 10.0.0.0/16
      Tags:
        - Key: Name
          Value: !Sub ${Environment}-vpc

Outputs:
  VPCId:
    Value: !Ref VPC
    Export:
      Name: !Sub ${Environment}-VPCId

Implementation

Deploy Stack

# Validate template
aws cloudformation validate-template \
  --template-body file://template.yaml

# Create stack
aws cloudformation create-stack \
  --stack-name my-stack \
  --template-body file://template.yaml \
  --parameters ParameterKey=Environment,ParameterValue=prod \
  --capabilities CAPABILITY_IAM CAPABILITY_NAMED_IAM \
  --tags Key=Environment,Value=Production \
  --enable-termination-protection

# Wait for completion
aws cloudformation wait stack-create-complete --stack-name my-stack

Update Stack

# Create change set (preview changes)
aws cloudformation create-change-set \
  --stack-name my-stack \
  --change-set-name my-changes \
  --template-body file://template.yaml \
  --parameters ParameterKey=Environment,ParameterValue=prod

# Review changes
aws cloudformation describe-change-set \
  --stack-name my-stack \
  --change-set-name my-changes

# Execute change set
aws cloudformation execute-change-set \
  --stack-name my-stack \
  --change-set-name my-changes

Nested Stacks Pattern

Resources:
  VPCStack:
    Type: AWS::CloudFormation::Stack
    Properties:
      TemplateURL: https://s3.amazonaws.com/bucket/vpc.yaml
      Parameters:
        Environment: !Ref Environment

  DatabaseStack:
    Type: AWS::CloudFormation::Stack
    DependsOn: VPCStack
    Properties:
      TemplateURL: https://s3.amazonaws.com/bucket/rds.yaml
      Parameters:
        VPCId: !GetAtt VPCStack.Outputs.VPCId

Troubleshooting

Common Issues

Debug Checklist

• Template valid (validate-template)?
• Required capabilities specified?
• Parameters have valid values?
• IAM has required permissions?
• Resource dependencies correct?
• No circular references?

Stack Events Analysis

# Get stack events
aws cloudformation describe-stack-events \
  --stack-name my-stack \
  --query 'StackEvents[?ResourceStatus==`CREATE_FAILED`]'

Common Errors

Resource handler returned message: ... → Provider-specific error
Circular dependency between resources → Use DependsOn carefully
Export ... cannot be updated → Update dependent stacks first
Template format error → Check YAML syntax

Best Practices

1. Use Change Sets: Always preview before updating
2. Enable Termination Protection: For production stacks
3. Use Nested Stacks: For reusable components
4. Export Outputs: For cross-stack references
5. Use Stack Policies: Protect critical resources
6. Version Templates: Store in Git

Test Template

def test_cloudformation_template():
    # Arrange
    template_body = open('template.yaml').read()

    # Act - Validate
    response = cfn.validate_template(TemplateBody=template_body)

    # Assert
    assert 'Parameters' in response
    assert response['Capabilities'] == ['CAPABILITY_IAM']

    # Act - Create stack (dry run)
    # Use change set with no execute for testing

Assets

• assets/vpc-template.yaml - Production VPC template

References

• CloudFormation User Guide
• Best Practices