AWS CloudFormation Skill Skill

AWS CloudFormation Skill

Create and manage infrastructure as code with CloudFormation.

Quick Reference

| Attribute | Value | |-----------|-------| | AWS Service | CloudFormation | | Complexity | Medium-High | | Est. Time | 10-60 min | | Prerequisites | IAM permissions |

Parameters

Required

| Parameter | Type | Description | Validation | |-----------|------|-------------|------------| | stack_name | string | Stack name | ^[a-zA-Z][-a-zA-Z0-9]{0,127}$ | | template_path | string | Template file path | Valid YAML/JSON |

Optional

| Parameter | Type | Default | Description | |-----------|------|---------|-------------| | parameters | object | {} | Stack parameters | | capabilities | array | [] | CAPABILITY_IAM, etc. | | tags | object | {} | Resource tags | | termination_protection | bool | false | Prevent deletion | | rollback_on_failure | bool | true | Rollback on error |

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

| Symptom | Cause | Solution | |---------|-------|----------| | CREATE_FAILED | Resource error | Check events for details | | UPDATE_ROLLBACK | Update failed | Review change set | | DELETE_FAILED | Resource in use | Remove dependencies | | ROLLBACK_COMPLETE | Creation failed | Delete and fix |

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

Use Change Sets: Always preview before updating
Enable Termination Protection: For production stacks
Use Nested Stacks: For reusable components
Export Outputs: For cross-stack references
Use Stack Policies: Protect critical resources
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

Agent Skills: AWS CloudFormation Skill

Skill Files