[...]
  ServerInstance:
    Type: "AWS::EC2::Instance"
    Properties:
      ImageId: "ami-0e1ab783dc9489f34" # Centos7 for paris
      InstanceType: t3.2xlarge
      AvailabilityZone: !GetAtt FortiVPCFrontNet.AvailabilityZone
      KeyName:
        Ref: KeyName
      SubnetId:
        Ref: FortiVPCBackNet
      SecurityGroupIds:
        - !Ref ServerSecGroup

  Server2Instance:
    Type: "AWS::EC2::Instance"
    Properties:
      ImageId: "ami-0e1ab783dc9489f34" # Centos7 for paris
      [...]