AWS Cloudformation Vpc

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

# Review change set before applying
aws cloudformation create-change-set \
  --stack-name my-vpc \
  --template-body file://vpc.yaml \
  --change-set-type CREATE

# Verify route table associations
aws ec2 describe-route-tables \
  --filters "Name=vpc-id,Values=<vpc-id>"

# Check subnet to route table mappings
aws ec2 describe-route-tables \
  --filters "Name=association.subnet-id,Values=<subnet-id>"

# Verify internet gateway attachment
aws ec2 describe-internet-gateways \
  --filters "Name=attachment.vpc-id,Values=<vpc-id>"

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

Resources:
  # VPC
  MainVpc:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: 10.0.0.0/16
      EnableDnsHostnames: true
      EnableDnsSupport: true
      Tags:
        - Key: Name
          Value: !Sub "${AWS::StackName}-main"

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

  # Attach IGW to VPC
  GatewayToInternet:
    Type: AWS::EC2::VPCGatewayAttachment
    Properties:
      VpcId: !Ref MainVpc
      InternetGatewayId: !Ref InternetGateway

  # Public Subnet (AZ 1)
  PublicSubnetA:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: !Ref MainVpc
      CidrBlock: 10.0.1.0/24
      AvailabilityZone: !Select [0, !GetAZs ""]
      MapPublicIpOnLaunch: true
      Tags:
        - Key: Name
          Value: !Sub "${AWS::StackName}-public-a"

  # Private Subnet (AZ 1)
  PrivateSubnetA:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: !Ref MainVpc
      CidrBlock: 10.0.11.0/24
      AvailabilityZone: !Select [0, !GetAZs ""]
      Tags:
        - Key: Name
          Value: !Sub "${AWS::StackName}-private-a"

  # Elastic IP for NAT Gateway
  NatEip:
    Type: AWS::EC2::EIP
    DependsOn: GatewayToInternet
    Properties:
      Domain: vpc

  # NAT Gateway
  NatGateway:
    Type: AWS::EC2::NatGateway
    Properties:
      SubnetId: !Ref PublicSubnetA
      AllocationId: !GetAtt NatEip.AllocationId

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

  # Default route to IGW
  PublicDefaultRoute:
    Type: AWS::EC2::Route
    DependsOn: GatewayToInternet
    Properties:
      RouteTableId: !Ref PublicRouteTable
      DestinationCidrBlock: 0.0.0.0/0
      GatewayId: !Ref InternetGateway

  # Associate public subnet
  PublicSubnetARouteTableAssociation:
    Type: AWS::EC2::SubnetRouteTableAssociation
    Properties:
      SubnetId: !Ref PublicSubnetA
      RouteTableId: !Ref PublicRouteTable

  # Private Route Table
  PrivateRouteTable:
    Type: AWS::EC2::RouteTable
    Properties:
      VpcId: !Ref MainVpc
      Tags:
        - Key: Name
          Value: !Sub "${AWS::StackName}-private-rt"

  # Default route via NAT Gateway
  PrivateDefaultRoute:
    Type: AWS::EC2::Route
    Properties:
      RouteTableId: !Ref PrivateRouteTable
      DestinationCidrBlock: 0.0.0.0/0
      NatGatewayId: !Ref NatGateway

  # Associate private subnet
  PrivateSubnetARouteTableAssociation:
    Type: AWS::EC2::SubnetRouteTableAssociation
    Properties:
      SubnetId: !Ref PrivateSubnetA
      RouteTableId: !Ref PrivateRouteTable

Outputs:
  VpcId:
    Description: VPC ID
    Value: !Ref MainVpc
    Export:
      Name: !Sub "${AWS::StackName}-VpcId"

  PublicSubnetA:
    Description: Public subnet AZ1
    Value: !Ref PublicSubnetA
    Export:
      Name: !Sub "${AWS::StackName}-PublicSubnetA"

  PrivateSubnetA:
    Description: Private subnet AZ1
    Value: !Ref PrivateSubnetA
    Export:
      Name: !Sub "${AWS::StackName}-PrivateSubnetA"

  PublicRouteTableId:
    Description: Public route table ID
    Value: !Ref PublicRouteTable
    Export:
      Name: !Sub "${AWS::StackName}-PublicRouteTableId"

  PrivateRouteTableId:
    Description: Private route table ID
    Value: !Ref PrivateRouteTable
    Export:
      Name: !Sub "${AWS::StackName}-PrivateRouteTableId"

Resources:
  # S3 VPC Endpoint
  S3Endpoint:
    Type: AWS::EC2::VPCEndpoint
    Properties:
      VpcId: !Ref MainVpc
      ServiceName: !Sub "com.amazonaws.${AWS::Region}.s3"
      RouteTableIds:
        - !Ref PrivateRouteTable
      VpcEndpointType: Gateway