CloudFormation Template Generator

CloudFormation Template Generator

Generates AWS CloudFormation templates from scratch or helps convert Terraform configurations to CloudFormation (with limitations).

When to Use This

• Organization requires CloudFormation
• Need to use AWS StackSets
• Migrating from Terraform to CloudFormation
• AWS Service Catalog integration
• Prefer Terraform (use Terraform instead!)
• Multi-cloud infrastructure (CFN is AWS-only)

How It Works

You are a CloudFormation expert. When user runs /cloudformation-generate or /cfn:

1. Understand requirements:

   • Starting from scratch OR converting from Terraform?
   • What AWS resources? (VPC, EC2, RDS, S3, etc.)
   • Parameters needed (make template reusable)?
   • Outputs required?

2. Generate CloudFormation structure:

   AWSTemplateFormatVersion: '2010-09-09'
   Description: [template description]
   
   Parameters:      # User inputs
   Mappings:        # Lookup tables (optional)
   Conditions:      # Conditional logic (optional)
   Resources:       # AWS resources (REQUIRED)
   Outputs:         # Return values
   

3. Apply CFN best practices:

   • Use parameters for reusability
   • Proper DependsOn for ordering
   • Use !Ref and !GetAtt for references
   • Add outputs for important values
   • Use conditions for multi-environment

4. Provide deployment guide:

   • CLI deployment commands
   • Console deployment steps
   • Parameter examples
   • Stack update procedures

Output Format

# Complete CloudFormation template
# Ready to deploy with aws cloudformation create-stack

## Deployment

### CLI:
```bash
aws cloudformation create-stack \
  --stack-name my-stack \
  --template-body file://template.yaml \
  --parameters [params]

Console:

[Step-by-step instructions]

## Example

**User:** `/cfn`

**Request:** Create VPC with public/private subnets, similar to Terraform VPC module

**Output:**

```yaml
AWSTemplateFormatVersion: '2010-09-09'
Description: 'VPC with public and private subnets across 2 AZs'

Parameters:
  VPCName:
    Description: Name of the VPC
    Type: String
    Default: MyVPC

  VPCCIDR:
    Description: CIDR block for VPC
    Type: String
    Default: 10.0.0.0/16
    AllowedPattern: ^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])(\/([0-9]|[1-2][0-9]|3[0-2]))$

  PublicSubnet1CIDR:
    Description: CIDR for public subnet in AZ1
    Type: String
    Default: 10.0.1.0/24

  PublicSubnet2CIDR:
    Description: CIDR for public subnet in AZ2
    Type: String
    Default: 10.0.2.0/24

  PrivateSubnet1CIDR:
    Description: CIDR for private subnet in AZ1
    Type: String
    Default: 10.0.11.0/24

  PrivateSubnet2CIDR:
    Description: CIDR for private subnet in AZ2
    Type: String
    Default: 10.0.12.0/24

  Environment:
    Description: Environment name
    Type: String
    Default: dev
    AllowedValues:
      - dev
      - staging
      - production

Conditions:
  IsProduction: !Equals [!Ref Environment, production]

Mappings:
  AZMapping:
    us-east-1:
      AZ1: us-east-1a
      AZ2: us-east-1b
    us-west-2:
      AZ1: us-west-2a
      AZ2: us-west-2b

Resources:
  # VPC
  VPC:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: !Ref VPCCIDR
      EnableDnsHostnames: true
      EnableDnsSupport: true
      Tags:
        - Key: Name
          Value: !Ref VPCName
        - Key: Environment
          Value: !Ref Environment

  # Internet Gateway
  InternetGateway:
    Type: AWS::EC2::InternetGateway
    Properties:
      Tags:
        - Key: Name
          Value: !Sub '${VPCName}-igw'

  AttachGateway:
    Type: AWS::EC2::VPCGatewayAttachment
    Properties:
      VpcId: !Ref VPC
      InternetGatewayId: !Ref InternetGateway

  # Public Subnets
  PublicSubnet1:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: !Ref VPC
      CidrBlock: !Ref PublicSubnet1CIDR
      AvailabilityZone: !FindInMap [AZMapping, !Ref 'AWS::Region', AZ1]
      MapPublicIpOnLaunch: true
      Tags:
        - Key: Name
          Value: !Sub '${VPCName}-public-1'
        - Key: Type
          Value: public

  PublicSubnet2:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: !Ref VPC
      CidrBlock: !Ref PublicSubnet2CIDR
      AvailabilityZone: !FindInMap [AZMapping, !Ref 'AWS::Region', AZ2]
      MapPublicIpOnLaunch: true
      Tags:
        - Key: Name
          Value: !Sub '${VPCName}-public-2'
        - Key: Type
          Value: public

  # Private Subnets
  PrivateSubnet1:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: !Ref VPC
      CidrBlock: !Ref PrivateSubnet1CIDR
      AvailabilityZone: !FindInMap [AZMapping, !Ref 'AWS::Region', AZ1]
      Tags:
        - Key: Name
          Value: !Sub '${VPCName}-private-1'
        - Key: Type
          Value: private

  PrivateSubnet2:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: !Ref VPC
      CidrBlock: !Ref PrivateSubnet2CIDR
      AvailabilityZone: !FindInMap [AZMapping, !Ref 'AWS::Region', AZ2]
      Tags:
        - Key: Name
          Value: !Sub '${VPCName}-private-2'
        - Key: Type
          Value: private

  # Elastic IPs for NAT Gateways
  NatGateway1EIP:
    Type: AWS::EC2::EIP
    DependsOn: AttachGateway
    Properties:
      Domain: vpc
      Tags:
        - Key: Name
          Value: !Sub '${VPCName}-nat-eip-1'

  NatGateway2EIP:
    Type: AWS::EC2::EIP
    DependsOn: AttachGateway
    Condition: IsProduction  # Only create second NAT in production
    Properties:
      Domain: vpc
      Tags:
        - Key: Name
          Value: !Sub '${VPCName}-nat-eip-2'

  # NAT Gateways
  NatGateway1:
    Type: AWS::EC2::NatGateway
    Properties:
      AllocationId: !GetAtt NatGateway1EIP.AllocationId
      SubnetId: !Ref PublicSubnet1
      Tags:
        - Key: Name
          Value: !Sub '${VPCName}-nat-1'

  NatGateway2:
    Type: AWS::EC2::NatGateway
    Condition: IsProduction
    Properties:
      AllocationId: !GetAtt NatGateway2EIP.AllocationId
      SubnetId: !Ref PublicSubnet2
      Tags:
        - Key: Name
          Value: !Sub '${VPCName}-nat-2'

  # Public Route Table
  PublicRouteTable:
    Type: AWS::EC2::RouteTable
    Properties:
      VpcId: !Ref VPC
      Tags:
        - Key: Name
          Value: !Sub '${VPCName}-public-rt'

  PublicRoute:
    Type: AWS::EC2::Route
    DependsOn: AttachGateway
    Properties:
      RouteTableId: !Ref PublicRouteTable
      DestinationCidrBlock: 0.0.0.0/0
      GatewayId: !Ref InternetGateway

  PublicSubnet1RouteTableAssociation:
    Type: AWS::EC2::SubnetRouteTableAssociation
    Properties:
      SubnetId: !Ref PublicSubnet1
      RouteTableId: !Ref PublicRouteTable

  PublicSubnet2RouteTableAssociation:
    Type: AWS::EC2::SubnetRouteTableAssociation
    Properties:
      SubnetId: !Ref PublicSubnet2
      RouteTableId: !Ref PublicRouteTable

  # Private Route Tables
  PrivateRouteTable1:
    Type: AWS::EC2::RouteTable
    Properties:
      VpcId: !Ref VPC
      Tags:
        - Key: Name
          Value: !Sub '${VPCName}-private-rt-1'

  PrivateRoute1:
    Type: AWS::EC2::Route
    Properties:
      RouteTableId: !Ref PrivateRouteTable1
      DestinationCidrBlock: 0.0.0.0/0
      NatGatewayId: !Ref NatGateway1

  PrivateSubnet1RouteTableAssociation:
    Type: AWS::EC2::SubnetRouteTableAssociation
    Properties:
      SubnetId: !Ref PrivateSubnet1
      RouteTableId: !Ref PrivateRouteTable1

  PrivateRouteTable2:
    Type: AWS::EC2::RouteTable
    Properties:
      VpcId: !Ref VPC
      Tags:
        - Key: Name
          Value: !Sub '${VPCName}-private-rt-2'

  PrivateRoute2:
    Type: AWS::EC2::Route
    Properties:
      RouteTableId: !Ref PrivateRouteTable2
      DestinationCidrBlock: 0.0.0.0/0
      NatGatewayId: !If [IsProduction, !Ref NatGateway2, !Ref NatGateway1]

  PrivateSubnet2RouteTableAssociation:
    Type: AWS::EC2::SubnetRouteTableAssociation
    Properties:
      SubnetId: !Ref PrivateSubnet2
      RouteTableId: !Ref PrivateRouteTable2

Outputs:
  VPCID:
    Description: VPC ID
    Value: !Ref VPC
    Export:
      Name: !Sub '${AWS::StackName}-VPCID'

  VPCCIDR:
    Description: VPC CIDR block
    Value: !GetAtt VPC.CidrBlock

  PublicSubnets:
    Description: Public subnet IDs (comma-separated)
    Value: !Join [',', [!Ref PublicSubnet1, !Ref PublicSubnet2]]
    Export:
      Name: !Sub '${AWS::StackName}-PublicSubnets'

  PrivateSubnets:
    Description: Private subnet IDs (comma-separated)
    Value: !Join [',', [!Ref PrivateSubnet1, !Ref PrivateSubnet2]]
    Export:
      Name: !Sub '${AWS::StackName}-PrivateSubnets'

  NatGatewayIPs:
    Description: NAT Gateway Elastic IPs
    Value: !If
      - IsProduction
      - !Join [',', [!Ref NatGateway1EIP, !Ref NatGateway2EIP]]
      - !Ref NatGateway1EIP

Deployment Instructions:

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

# 2. Create stack (development)
aws cloudformation create-stack \
  --stack-name myapp-vpc-dev \
  --template-body file://vpc-template.yaml \
  --parameters \
    ParameterKey=VPCName,ParameterValue=myapp-dev \
    ParameterKey=Environment,ParameterValue=dev

# 3. Create stack (production)
aws cloudformation create-stack \
  --stack-name myapp-vpc-prod \
  --template-body file://vpc-template.yaml \
  --parameters \
    ParameterKey=VPCName,ParameterValue=myapp-prod \
    ParameterKey=Environment,ParameterValue=production

# 4. Check stack status
aws cloudformation describe-stacks --stack-name myapp-vpc-dev

# 5. Get outputs
aws cloudformation describe-stacks \
  --stack-name myapp-vpc-dev \
  --query 'Stacks[0].Outputs'

# 6. Update stack
aws cloudformation update-stack \
  --stack-name myapp-vpc-dev \
  --template-body file://vpc-template.yaml \
  --parameters [same as create]

# 7. Delete stack
aws cloudformation delete-stack --stack-name myapp-vpc-dev

Key CFN Features Used

Parameters:

• Make template reusable across environments
• Validation with AllowedPattern, AllowedValues
• Default values for convenience

Conditions:

• IsProduction creates second NAT only in prod (cost savings)
• !If function for conditional resource references

Mappings:

• AZMapping for region-specific availability zones
• Makes template portable across regions

Intrinsic Functions:

• !Ref - Reference parameters or resources
• !GetAtt - Get attribute from resource
• !Sub - String substitution
• !Join - Concatenate values
• !FindInMap - Lookup from mapping

Outputs with Exports:

• Export values for cross-stack references
• Other stacks can import with !ImportValue

Terraform vs CloudFormation

Pro Tips

Use parameters for reusability Export outputs for cross-stack references Use conditions for environment differences Always use DependsOn for correct ordering Validate template before deploying

Common Conversions

Terraform → CloudFormation:

# Terraform
resource "aws_s3_bucket" "assets" {
  bucket = "myapp-assets"
}

# CloudFormation
Resources:
  AssetsBucket:
    Type: AWS::S3::Bucket
    Properties:
      BucketName: myapp-assets