AWSTemplateFormatVersion: 2010-09-09

# This CloudFormation template deploys a basic VPC / Network.  Specifically:
# It deploys a VPC with 4 subnets (2 public, 2 private) across 2 Availability Zones
# A NAT Gateway is used to provide egress for private subnets.
# The VPC and subnets are exported for use by other stacks.


Resources:

  # First, a VPC:
  VPC:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: 10.10.0.0/16
      EnableDnsSupport: true
      EnableDnsHostnames: true
      Tags:
      - Key: Name
        Value:  !Join ['', [!Ref "AWS::StackName", "" ]]

  # Our VPC will need internet access:      
  InternetGateway:
    Type: AWS::EC2::InternetGateway
    DependsOn: VPC
  AttachGateway:
    Type: AWS::EC2::VPCGatewayAttachment
    # Notice how you can't attach an IGW to a VPC unless both are created:
    Properties:
      VpcId: !Ref VPC
      InternetGatewayId: !Ref InternetGateway

  # Now some subnets, 2 public and 2 private:
  PublicSubnetA:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: !Ref VPC
      CidrBlock: 10.10.1.0/24
      AvailabilityZone: !Select [ 0, !GetAZs ]    # Get the first AZ in the list        
      Tags:
      - Key: Name
        Value: !Sub ${AWS::StackName}-Public-A
  PublicSubnetB:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: !Ref VPC
      CidrBlock: 10.10.2.0/24
      AvailabilityZone: !Select [ 1, !GetAZs ]    # Get the second AZ in the list  
      Tags:
      - Key: Name
        Value: !Sub ${AWS::StackName}-Public-B
  PrivateSubnetA:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: !Ref VPC
      CidrBlock: 10.10.3.0/24
      AvailabilityZone: !Select [ 0, !GetAZs ]    # Get the first AZ in the list  
      Tags:
      - Key: Name
        Value: !Sub ${AWS::StackName}-Private-A
  PrivateSubnetB:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: !Ref VPC
      CidrBlock: 10.10.4.0/24
      AvailabilityZone: !Select [ 1, !GetAZs ]    # Get the second AZ in the list  
      Tags:
      - Key: Name
        Value: !Sub ${AWS::StackName}-Private-B
        
  # Some route tables for our subnets:
  PublicRouteTable:
    Type: AWS::EC2::RouteTable
    Properties:
      VpcId: !Ref VPC
      Tags:
      - Key: Name
        Value: Public
  PublicRoute1:   # Public route table has direct routing to IGW:
    Type: AWS::EC2::Route
    DependsOn: AttachGateway
    Properties:
      RouteTableId: !Ref PublicRouteTable
      DestinationCidrBlock: 0.0.0.0/0
      GatewayId: !Ref InternetGateway
      
  # Here is a private route table:
  PrivateRouteTable:
    Type: AWS::EC2::RouteTable
    Properties:
      VpcId: !Ref VPC
      Tags:
      - Key: Name
        Value: Private
  PrivateRoute1:            # Private route table can access web via NAT (created below)
    Type: AWS::EC2::Route
    Properties:
      RouteTableId: !Ref PrivateRouteTable
      DestinationCidrBlock: 0.0.0.0/0
      # Route traffic through the NAT Gateway:
      NatGatewayId: !Ref NATGateway

  # Attach the public subnets to public route tables, 
  # and attach the private subnets to private route tables:    
  PublicSubnetARouteTableAssociation:
    Type: AWS::EC2::SubnetRouteTableAssociation
    Properties:
      SubnetId: !Ref PublicSubnetA
      RouteTableId: !Ref PublicRouteTable
  PublicSubnetBRouteTableAssociation:
    Type: AWS::EC2::SubnetRouteTableAssociation
    Properties:
      SubnetId: !Ref PublicSubnetB
      RouteTableId: !Ref PublicRouteTable
  PrivateSubnetARouteTableAssociation:
    Type: AWS::EC2::SubnetRouteTableAssociation
    Properties:
      SubnetId: !Ref PrivateSubnetA
      RouteTableId: !Ref PrivateRouteTable
  PrivateSubnetBRouteTableAssociation:
    Type: AWS::EC2::SubnetRouteTableAssociation
    Properties:
      SubnetId: !Ref PrivateSubnetB
      RouteTableId: !Ref PrivateRouteTable

  #A NAT Gateway: 
  NATGateway:
    Type: AWS::EC2::NatGateway
    Properties: 
      AllocationId: !GetAtt ElasticIPAddress.AllocationId
      SubnetId: !Ref PublicSubnetA
      Tags: 
      - Key: Name
        Value: !Sub NAT-${AWS::StackName}
  ElasticIPAddress:
    Type: AWS::EC2::EIP
    Properties:
      Domain: VPC