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Deploying Network Infrastructures in AWS Using CloudFormation

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AWS is undoubtedly the most complete cloud services provider. Even though its services are not always the best compared to other similar services, it is able to provide a variety of tools to help us build any kind of internet-based services. When we initially create an account in AWS, we instantly receive the ability to create a complex network within a Virtual Private Cloud (VPC). We can develop a VPC in a region on multiple data centers or availability zones. AWS allows us to configure and deploy our infrastructures using an IaC-based (Infrastructure as Code) service called CloudFormation.

For instance, we will deploy a VPC with several network components in it. The components include internet gateway, subnet, NAT gateway, and routing tables. The VPC will be available in a single availability zone and hosts two subnets which are private and public.


Firstly, we define the variables that will be referred to in the configuration within the Parameters block. It contains only the declaration of the variable's names. The related values will be stored in a different file.

# file: network.yml

Parameters:
  ProjectName:
    Description: Name of the project
    Type: String
  VpcCIDR:
    Description: CIDR of VPC
    Type: String
    Default: 10.0.0.0/16
  PrivateSubnetCIDR:
    Description: CIDR of private subnet
    Type: String
    Default: 10.0.1.0/24
  PublicSubnetCIDR:
    Description: CIDR of public subnet
    Type: String
    Default: 10.0.2.0/24

For example, we store the values in the network-params.json file.

[
  {
    "ParameterKey": "ProjectName",
    "ParameterValue": "MyProject"
  },
  {
    "ParameterKey": "VpcCIDR",
    "ParameterValue": "10.0.0.0/16"
  },
  {
    "ParameterKey": "PrivateSubnetCIDR",
    "ParameterValue": "10.0.0.0/24"
  },
  {
    "ParameterKey": "PublicSubnetCIDR",
    "ParameterValue": "10.0.128.0/24"
  }
]

Now, we will define all resources in the Resources block. The first component that is required to be defined is the VPC itself. The component's name is up to us. In this example, it is named as VPC. The most important property is the type. For deploying the VPC it should be AWS::EC2::VPC. CloudFormation can translate a reference by using the !Ref function. We can refer to other resources' names or configuration parameter names by using the same function. 

  VPC:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: !Ref VpcCIDR
      EnableDnsSupport: true
      EnableDnsHostnames: true
      Tags:
        - Key: Name
          Value: !Ref ProjectName

Then, we need to deploy an internet gateway and attach it to the VPC network. The internet gateway is required to allow all components in our network to communicate with the outside world through the internet. 

  InetGW:
    Type: AWS::EC2::InternetGateway
    Properties:
      Tags:
        - Key: Name
          Value: !Ref ProjectName
  
  InetGWAttachment:
    Type: AWS::EC2::VPCGatewayAttachment
    Properties:
      InternetGatewayId: !Ref InetGW
      VpcId: !Ref VPC

The next are the subnets. The private subnet doesn't need to provide public IP addresses while the public subnet needs it. The !Sub function is used in a text to transform the parameter to the referred value. CloudFormation is shipped to support many built-in functions, one of them is the !GetAZs function for retrieving the list of availability zones (AZ) in a region. In this example, we take only the first result because we deploy the subnets in a single AZ. 

  PrivateSubnet:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: !Ref VPC
      CidrBlock: !Ref PrivateSubnetCIDR
      AvailabilityZone: !Select [0, !GetAZs '']
      MapPublicIpOnLaunch: false
      Tags:
        - Key: Name
          Value: !Sub ${ProjectName} Private Subnet (AZ1)
  
  PublicSubnet:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: !Ref VPC
      CidrBlock: !Ref PublicSubnetCIDR
      AvailabilityZone: !Select [0, !GetAZs '']
      MapPublicIpOnLaunch: true
      Tags:
        - Key: Name
          Value: !Sub ${ProjectName} Public Subnet (AZ1)

The resources in the private subnet typically still need some dependencies which may be available only on the internet. Therefore, we need to deploy a NAT gateway that allows outbound traffic from private resources. The NAT gateway should be deployed on the public subnet so that it can access the internet. It also requires an allocated IP for allowing inbound traffic from specific clients that need to access the private resources. 

  NatGatewayEIP:
    Type: AWS::EC2::EIP
    DependsOn: InetGWAttachment
    Properties:
      Domain: vpc
  
  NatGateway:
    Type: AWS::EC2::NatGateway
    Properties:
      AllocationId: !GetAtt NatGatewayEIP.AllocationId
      SubnetId: !Ref PublicSubnet

We need route tables for public and private subnets so that the gateways can direct traffic correctly. The route table can host multiple route configurations. Then, we need to define the association between a routing table and a subnet. In the public routing configuration, we use the GatewayId property. Meanwhile, in the private routing configuration, we use the NatGatewayId property. 

  PublicRouteTable:
    Type: AWS::EC2::RouteTable
    Properties:
      VpcId: !Ref VPC
      Tags:
        - Key: Name
          Value: !Sub ${ProjectName} Public Routing

  DefaultPublicRoute:
    Type: AWS::EC2::Route
    DependsOn: InetGWAttachment
    Properties:
      RouteTableId: !Ref PublicRouteTable
      DestinationCidrBlock: 0.0.0.0/0
      GatewayId: !Ref InetGW
  
  PublicSubnetRouteTableAssociation:
    Type: AWS::EC2::SubnetRouteTableAssociation
    Properties:
      RouteTableId: !Ref PublicRouteTable
      SubnetId: !Ref PublicSubnet
  
  PrivateRouteTable:
    Type: AWS::EC2::RouteTable
    Properties:
      VpcId: !Ref VPC
      Tags:
        - Key: Name
          Value: !Sub ${ProjectName} Private Routing AZ1
  
  DefaultPrivateRoute:
    Type: AWS::EC2::Route
    Properties:
      RouteTableId: !Ref PrivateRouteTable
      DestinationCidrBlock: 0.0.0.0/0
      NatGatewayId: !Ref NatGateway
  
  PrivateSubnetRouteTableAssociation:
    Type: AWS::EC2::SubnetRouteTableAssociation
    Properties:
      RouteTableId: !Ref PrivateRouteTable
      SubnetId: !Ref PrivateSubnet

After we define all resources, we may need to know the IDs of the deployed components or the allocated IPs of the elastic IP resources. The values can also be referred to by other stack declarations within different configuration files. We can expose those values by declaring custom output variables in the Outputs block. The values are accessed by other files using their exported names.

  oVPC:
    Description: Reference to created VPC
    Value: !Ref VPC
    Export:
      Name: !Sub ${ProjectName}-VPCID

  oVPCPublicRouteTable:
    Description: Public Routing
    Value: !Ref PublicRouteTable
    Export:
      Name: !Sub ${ProjectName}-PubRouteID

  oVPCPrivateRouteTable:
    Description: Private Routing AZ1
    Value: !Ref PrivateRouteTable
    Export:
      Name: !Sub ${ProjectName}-PrivRouteID
  
  oPublicSubnets:
    Description: List of public subnets
    Value: !Join [ ',', [!Ref PublicSubnet] ]
    Export:
      Name: !Sub ${ProjectName}-PubNets

  oPrivateSubnets:
    Description: List of private subnets
    Value: !Join [ ',', [!Ref PrivateSubnet] ]
    Export:
      Name: !Sub ${ProjectName}-PrivNets
  
  oNatGatewayEIP:
    Description: Elastic IP address of the NAT gateway
    Value: !Ref NatGatewayEIP
    Export:
      Name: !Sub ${ProjectName}-NatGatewayEIP

Lastly, we can deploy the infrastructures using the AWS CLI tool.

aws --region ap-southeast-1 cloudformation create-stack \
  --stack-name myStack \
  --template-body file://network.yml \
  --parameters file://network-params.json

The final configuration file that we run is as follows.

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