public-private.yaml

---
AWSTemplateFormatVersion: '2010-09-09'
Description: Create one public and one private subnet. Can create a VPC or use an existing one.

### Stack metadata
Metadata:
  AWS::CloudFormation::Interface:
    ParameterGroups:
      - Label:
          default: VPC
        Parameters:
          - AvailabilityZone
          - VpcCIDR
          - VpcId
          - InternetGatewayId
      - Label:
          default: Subnets
        Parameters:
          - PublicCIDR
          - PrivateCIDR

Parameters:
  AvailabilityZone:
    Description: "(Optional) Availability Zone in which you want to create your subnet(s). Required if you opt to create a VPC."
    Type: String
  InternetGatewayId:
    Description: "(Optional) The id of the Internet Gateway. Required if using an existing VPC."
    Type: String
    Default: ''
  PrivateCIDR:
    AllowedPattern: "\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}/(1[6-9]|2[0-9]|3[0-2])$"
    Description: CIDR block for the private subnet
    Default: 10.0.16.0/20
    Type: String
  PublicCIDR:
    AllowedPattern: "\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}/(1[6-9]|2[0-9]|3[0-2])$"
    Description: CIDR block for the public subnet
    Default: 10.0.0.0/24
    Type: String
  VpcId:
    Description: "(Optional) The VPC to create subnets in. Leave blank to create a new VPC."
    Default: ''
    Type: String
  VpcCIDR:
    Description: "CIDR block for the VPC if it will be created. Required if you opt to create a VPC."
    Default: 10.0.0.0/16
    Type: String

Conditions:
  CreateInternetGateway:
    Fn::Equals:
    - Ref: InternetGatewayId
    - ''
  CreateVpc:
    Fn::Equals:
    - Ref: VpcId
    - ''
  ExistingInternetGateway:
    Fn::Not:
    - Fn::Equals:
      - Ref: InternetGatewayId
      - ''

Resources:
  Vpc:
    Condition: CreateVpc
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock:
        Ref: VpcCIDR
      EnableDnsHostnames: true
      EnableDnsSupport: true
      Tags:
        - Key: "Name"
          Value: !Sub '${AWS::StackName}:Basic-HPC'

  DefaultRouteDependsOnPublic:
    Condition: CreateInternetGateway
    DependsOn: VPCGatewayAttachment
    Properties:
      DestinationCidrBlock: 0.0.0.0/0
      GatewayId:
        Fn::If:
        - CreateInternetGateway
        - Ref: InternetGateway
        - Ref: InternetGatewayId
      RouteTableId:
        Ref: RouteTablePublic
    Type: AWS::EC2::Route

  DefaultRouteNoDependsOnPublic:
    Condition: ExistingInternetGateway
    Properties:
      DestinationCidrBlock: 0.0.0.0/0
      GatewayId:
        Fn::If:
        - CreateInternetGateway
        - Ref: InternetGateway
        - Ref: InternetGatewayId
      RouteTableId:
        Ref: RouteTablePublic
    Type: AWS::EC2::Route

  InternetGateway:
    Condition: CreateInternetGateway
    Properties:
      Tags:
      - Key: Name
        Value: !Sub '${AWS::StackName}:InternetGateway'
      - Key: Stack
        Value:
          Ref: AWS::StackId
    Type: AWS::EC2::InternetGateway

  NatEIPPublic:
    Properties:
      Domain: vpc
    Type: AWS::EC2::EIP

  NatGatewayPublic:
    Properties:
      AllocationId:
        Fn::GetAtt:
        - NatEIPPublic
        - AllocationId
      SubnetId:
        Ref: Public
    Type: AWS::EC2::NatGateway

  NatRoutePrivate:
    Properties:
      DestinationCidrBlock: 0.0.0.0/0
      NatGatewayId:
        Ref: NatGatewayPublic
      RouteTableId:
        Ref: RouteTablePrivate
    Type: AWS::EC2::Route

  Private:
    Properties:
      AvailabilityZone:
        Ref: AvailabilityZone
      CidrBlock:
        Ref: PrivateCIDR
      MapPublicIpOnLaunch: false
      Tags:
      - Key: Name
        Value: !Sub '${AWS::StackName}:PrivateSubnetA-${AvailabilityZone}'
      - Key: Stack
        Value:
          Ref: AWS::StackId
      VpcId:
        Fn::If:
        - CreateVpc
        - Ref: Vpc
        - Ref: VpcId
    Type: AWS::EC2::Subnet

  Public:
    Properties:
      AvailabilityZone:
        Ref: AvailabilityZone
      CidrBlock:
        Ref: PublicCIDR
      MapPublicIpOnLaunch: true
      Tags:
      - Key: Name
        Value: !Sub '${AWS::StackName}:PublicSubnetA-${AvailabilityZone}'
      - Key: Stack
        Value:
          Ref: AWS::StackId
      VpcId:
        Fn::If:
        - CreateVpc
        - Ref: Vpc
        - Ref: VpcId
    Type: AWS::EC2::Subnet

  RouteAssociationPrivate:
    Properties:
      RouteTableId:
        Ref: RouteTablePrivate
      SubnetId:
        Ref: Private
    Type: AWS::EC2::SubnetRouteTableAssociation

  RouteAssociationPublic:
    Properties:
      RouteTableId:
        Ref: RouteTablePublic
      SubnetId:
        Ref: Public
    Type: AWS::EC2::SubnetRouteTableAssociation

  RouteTablePrivate:
    Properties:
      Tags:
      - Key: Name
        Value: !Sub '${AWS::StackName}:PrivateRoute'
      - Key: Stack
        Value:
          Ref: AWS::StackId
      VpcId:
        Fn::If:
        - CreateVpc
        - Ref: Vpc
        - Ref: VpcId
    Type: AWS::EC2::RouteTable

  RouteTablePublic:
    Properties:
      Tags:
      - Key: Name
        Value: !Sub '${AWS::StackName}:PublicRoute'
      - Key: Stack
        Value:
          Ref: AWS::StackId
      VpcId:
        Fn::If:
        - CreateVpc
        - Ref: Vpc
        - Ref: VpcId
    Type: AWS::EC2::RouteTable

  VPCGatewayAttachment:
    Condition: CreateInternetGateway
    Properties:
      InternetGatewayId:
        Ref: InternetGateway
      VpcId:
        Fn::If:
        - CreateVpc
        - Ref: Vpc
        - Ref: VpcId
    Type: AWS::EC2::VPCGatewayAttachment

Outputs:
  VPC:
    Value:
      Fn::If:
        - CreateVpc
        - Ref: Vpc
        - Ref: VpcId
    Description: ID of the VPC
    Export:
      Name: !Sub ${AWS::StackName}-VPC
  DefaultPrivateSubnet:
    Description: The ID of a default private subnet
    Value: !Ref Private
    Export:
      Name: !Sub "${AWS::StackName}-DefaultPrivateSubnet"
  DefaultPublicSubnet:
    Description: The ID of a default public subnet
    Value: !Ref Public
    Export:
      Name: !Sub "${AWS::StackName}-DefaultPublicSubnet"
  InternetGatewayId:
    Description: The ID of the Internet Gateway
    Value: 
      Fn::If:
        - CreateInternetGateway
        - Ref: InternetGateway
        - Ref: InternetGatewayId
    Export:
      Name: !Sub "${AWS::StackName}-InternetGateway"