Agent Skills: Validate template

When to use this skill

Use this skill whenever the user wants to:

• Write or debug CloudFormation templates (YAML/JSON)
• Create and manage AWS resources (EC2, S3, RDS, Lambda, etc.)
• Configure CloudFormation stacks, nested stacks, or stack sets
• Implement infrastructure automation with CloudFormation best practices
• Use cross-stack references with Export/ImportValue

How to use this skill

Workflow

1. Define template — write YAML with Parameters, Resources, and Outputs
2. Create change set — preview changes before applying
3. Deploy stack — create or update the stack
4. Validate — check stack events and outputs

Quick Start Example

AWSTemplateFormatVersion: '2010-09-09'
Description: Simple S3 bucket with versioning

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

Resources:
  AppBucket:
    Type: AWS::S3::Bucket
    Properties:
      BucketName: !Sub 'myapp-${Environment}-assets'
      VersioningConfiguration:
        Status: Enabled

Outputs:
  BucketArn:
    Value: !GetAtt AppBucket.Arn
    Export:
      Name: !Sub '${Environment}-AppBucketArn'

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

# Create stack with change set preview
aws cloudformation deploy \
  --template-file template.yaml \
  --stack-name myapp-dev \
  --parameter-overrides Environment=dev

Cross-Stack Reference Example

# In consuming stack — import the exported bucket ARN
Resources:
  LambdaFunction:
    Type: AWS::Lambda::Function
    Properties:
      Environment:
        Variables:
          BUCKET_ARN: !ImportValue dev-AppBucketArn

Best Practices

• Use YAML over JSON for readability and version control
• Store sensitive values with Parameter + NoEcho or AWS Secrets Manager — never hardcode
• Use Mappings and Conditions for environment-specific configuration
• Prefix stack names with environment (e.g., dev-, prod-) to avoid conflicts
• Encapsulate reusable resources as nested stacks for composability

Troubleshooting

• Rollback on create: Check stack events in CloudFormation console for the specific resource failure
• Circular dependency: Refactor with DependsOn or split resources across stacks
• Drift detection: Run aws cloudformation detect-stack-drift to find out-of-band changes

Keywords

cloudformation, aws, infrastructure as code, cloudformation template, aws iac, nested stacks, cross-stack references