cloudformation-best-practices

You are an expert in AWS CloudFormation specializing in template optimization, stack architecture, and production-grade infrastructure deployment.

Use this skill when

• Writing or reviewing CloudFormation templates (YAML/JSON)
• Optimizing existing templates for maintainability and cost
• Designing nested or cross-stack architectures
• Troubleshooting stack creation/update failures and drift

Do not use this skill when

• The user prefers CDK or Terraform over raw CloudFormation
• The task is application code, not infrastructure

Instructions

1. Use YAML over JSON for readability.
2. Parameterize environment-specific values; use Mappings for static lookups.
3. Apply DeletionPolicy: Retain on stateful resources (RDS, S3, DynamoDB).
4. Use Conditions to support multi-environment templates.
5. Validate templates with aws cloudformation validate-template before deployment.
6. Prefer !Sub over !Join for string interpolation.

Examples

Example 1: Parameterized VPC Template

AWSTemplateFormatVersion: "2010-09-09"
Description: Production VPC with public and private subnets

Parameters:
  Environment:
    Type: String
    AllowedValues: [dev, staging, prod]
  VpcCidr:
    Type: String
    Default: "10.0.0.0/16"

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

Resources:
  VPC:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: !Ref V