stack-designer

# Stack Designer

## Quick Start

Design well-organized CloudFormation stacks with proper resource grouping, parameters, outputs, and cross-stack references.

## Instructions

### Step 1: Identify stack boundaries

Determine how to organize resources into stacks:

**By lifecycle:**
- Resources that change together should be in the same stack
- Separate frequently updated resources from stable infrastructure
- Group by deployment frequency

**By ownership:**
- Network stack (VPC, subnets, route tables)
- Security stack (security groups, IAM roles)
- Application stack (EC2, ECS, Lambda)
- Data stack (RDS, DynamoDB, S3)

**By environment:**
- Separate dev, staging, production stacks
- Use parameters for environment-specific values
- Share common resources via cross-stack references

### Step 2: Design stack structure

**Simple stack (single template):**
```yaml
AWSTemplateFormatVersion: '2010-09-09'
Description: Simple web application stack

Parameters:
  EnvironmentName:
    Type: String
    Default: dev
    AllowedValues: [dev, staging, prod]
  
  InstanceType:
    Type: String
    Default: t3.micro
    AllowedValues: [t3.micro, t3.small, t3.medium]

Resources:
  WebServer:
    Type: AWS::EC2::Instance
    Properties:
      InstanceType: !Ref InstanceType
      ImageId: !Sub '{{resolve:ssm:/aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2}}'
      Tags:
        - Key: Environment
          Value: !Ref EnvironmentName

Outputs:
  InstanceId:
    Description: EC2 instance ID
    Value: !Ref WebServer
    Export:
      Name: !Sub '${AWS::StackName}-InstanceId'
```

**Multi-stack architecture:**
```
Root Stack
├── Network Stack (VPC, subnets)
├── Security Stack (security groups, IAM)
├── Database Stack (RDS)
└── Application Stack (EC2, ALB)
```

### Step 3: Define parameters

**Parameter best practices:**
```yaml
Parameters:
  # Use descriptive names
  DatabaseInstanceClass:
    Type: String
    Default: db.t3.micro
    AllowedValues:
      - db.t3.micro