code: function buildSubnet(name, position, zone, cidrBlock) {
    const cfName = `${name}Subnet${position}`;
    return {
      [cfName]: {
        Type: 'AWS::EC2::Subnet',
        Properties: {
          AvailabilityZone: zone,
          CidrBlock: cidrBlock,
          Tags: [
            {
              Key: 'Name',
              Value: {
                'Fn::Join': [
                  '-',
                  [
                    {
                      Ref: 'AWS::StackName',
                    },
                    name.toLowerCase(),
                    zone,
                  ],
                ],
              },
            },
          ],
          VpcId: {
            Ref: 'VPC',
          },
        },
      },
    };
  }
docs: Create a subnet
  
  @param {String} name Name of subnet
  @param {Number} position Subnet position
  @param {String} zone Availability zone
  @param {String} cidrBlock Subnet CIDR block
  @return {Object}