Scenario:

• Create a vpc
  • Add 3 subnets to vpc [Refer to previous classes screenshots]
  • Create and attach internet gateway to vpc
  • Create a Route table with route to internet gateway
  • Create subnet associations to new route table for 2 out 3 subnets
  • Create a Key value pair [manual] and security group [manual]
• Create an ec2 instance in subnet1 and other ec2 instance in subnet2 [last step] and ensure this solution works on us-west-2, us-east-1 and ap-south-1
• With every region in aws Image id /AMI id changes
• AWS has a reference {‘Ref’: "AWS::Region" } which gives you current region
• AWS supports Mappings Refer Here
• The cloud formation template looks as shown below

{
    "AWSTemplateFormatVersion": "2010-09-09",
    "Description": "This template is written for learning and it creates s3 bucket and ec2 instance",
    "Parameters": {
        "keypair": {
            "Description": "key pair for ec2 instance",
            "Type": "AWS::EC2::KeyPair::KeyName"
        },
        "instancetype": {
            "Type": "String",
            "AllowedValues": [
                "t2.micro",
                "t2.nano"
            ]
        },
        "subnet1AZ": {
            "Type": "AWS::EC2::AvailabilityZone::Name"
        },
        "subnet2AZ": {
            "Type": "AWS::EC2::AvailabilityZone::Name"
        },
        "subnet3AZ": {
            "Type": "AWS::EC2::AvailabilityZone::Name"
        }
    },
    "Mappings": {
        "AMIRegionMap": {
            "us-west-2": {
                "ubuntu18": "ami-003634241a8fcdec0"
            },
            "us-west-1": {
                "ubuntu18": "ami-0f56279347d2fa43e"
            },
            "us-east-2": {
                "ubuntu18": "ami-07c1207a9d40bc3bd"
            },
            "us-east-1": {
                "ubuntu18": "ami-085925f297f89fce1"
            },
            "ap-south-1": {
                "ubuntu18": "ami-0b44050b2d893d5f7"
            }
        }
    },
    "Resources": {
        "mynetwork": {
            "Type": "AWS::EC2::VPC",
            "Properties": {
                "CidrBlock": "10.10.0.0/16",
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "my network"
                    }
                ]
            }
        },
        "subnet1": {
            "Type": "AWS::EC2::Subnet",
            "Properties": {
                "AvailabilityZone": {
                    "Ref": "subnet1AZ"
                },
                "VpcId": {
                    "Ref": "mynetwork"
                },
                "CidrBlock": "10.10.0.0/24",
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "subnet1"
                    }
                ]
            }
        },
        "subnet2": {
            "Type": "AWS::EC2::Subnet",
            "Properties": {
                "AvailabilityZone": {
                    "Ref": "subnet2AZ"
                },
                "VpcId": {
                    "Ref": "mynetwork"
                },
                "CidrBlock": "10.10.1.0/24",
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "subnet2"
                    }
                ]
            }
        },
        "subnet3": {
            "Type": "AWS::EC2::Subnet",
            "Properties": {
                "AvailabilityZone": {
                    "Ref": "subnet3AZ"
                },
                "VpcId": {
                    "Ref": "mynetwork"
                },
                "CidrBlock": "10.10.2.0/24",
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "subnet2"
                    }
                ]
            }
        },
        "myigw": {
            "Type": "AWS::EC2::InternetGateway",
            "Properties": {
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "myigw"
                    }
                ]
            }
        },
        "AttachGateway": {
            "Type": "AWS::EC2::VPCGatewayAttachment",
            "Properties": {
                "VpcId": {
                    "Ref": "mynetwork"
                },
                "InternetGatewayId": {
                    "Ref": "myigw"
                }
            }
        },
        "myroutetable": {
            "Type": "AWS::EC2::RouteTable",
            "Properties": {
                "VpcId": {
                    "Ref": "mynetwork"
                },
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "my rt"
                    }
                ]
            }
        },
        "routeName": {
            "Type": "AWS::EC2::Route",
            "Properties": {
                "RouteTableId": {
                    "Ref": "myroutetable"
                },
                "DestinationCidrBlock": "0.0.0.0/0",
                "GatewayId": {
                    "Ref": "myigw"
                }
            }
        },
        "routeTableAssocName": {
            "Type": "AWS::EC2::SubnetRouteTableAssociation",
            "Properties": {
                "SubnetId": {
                    "Ref": "subnet1"
                },
                "RouteTableId": {
                    "Ref": "myroutetable"
                }
            }
        },
        "InstanceSecurityGroup": {
            "Type": "AWS::EC2::SecurityGroup",
            "Properties": {
                "GroupDescription": "Allow ssh to client host",
                "VpcId": {
                    "Ref": "mynetwork"
                },
                "SecurityGroupIngress": [
                    {
                        "IpProtocol": "tcp",
                        "FromPort": 22,
                        "ToPort": 22,
                        "CidrIp": "0.0.0.0/0"
                    }
                ]
            }
        },
        "myweb": {
            "Type": "AWS::EC2::Instance",
            "Properties": {
                "KeyName": {
                    "Ref": "keypair"
                },
                "ImageId": {
                    "Fn::FindInMap": [
                        "AMIRegionMap",
                        {
                            "Ref": "AWS::Region"
                        },
                        "ubuntu18"
                    ]
                },
                "InstanceType": {
                    "Ref": "instancetype"
                },
                "NetworkInterfaces": [
                    {
                        "AssociatePublicIpAddress": "true",
                        "DeviceIndex": "0",
                        "GroupSet": [
                            {
                                "Ref": "InstanceSecurityGroup"
                            }
                        ],
                        "SubnetId": {
                            "Ref": "subnet1"
                        }
                    }
                ],
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "myweb"
                    }
                ]
            }
        }
    }
}

• Now use this template to create stacks in atleast two regions

CloudFormation Functions

• Refer Here
• Lets try to show the public ip address of the ec2 machine in the outputs
• To do this we need to use Fn::GetAtt function and also look into the reference and Fn::GetAtt section of any resource
• using GetAtt function as defined over here
• Lets add the following to the template written above

,
    "Outputs": {
        "publicip": {
            "Value": {
                "Fn::GetAtt": [
                    "myweb",
                    "PublicIp"
                ]
            }
        },
        "privateip": {
            "Value": {
                "Fn::GetAtt": [
                    "myweb",
                    "PrivateIp"
                ]
            }
        }
    }

• The complete template

{
    "AWSTemplateFormatVersion": "2010-09-09",
    "Description": "This template is written for learning and it creates s3 bucket and ec2 instance",
    "Parameters": {
        "keypair": {
            "Description": "key pair for ec2 instance",
            "Type": "AWS::EC2::KeyPair::KeyName"
        },
        "instancetype": {
            "Type": "String",
            "AllowedValues": [
                "t2.micro",
                "t2.nano"
            ]
        },
        "subnet1AZ": {
            "Type": "AWS::EC2::AvailabilityZone::Name"
        },
        "subnet2AZ": {
            "Type": "AWS::EC2::AvailabilityZone::Name"
        },
        "subnet3AZ": {
            "Type": "AWS::EC2::AvailabilityZone::Name"
        }
    },
    "Mappings": {
        "AMIRegionMap": {
            "us-west-2": {
                "ubuntu18": "ami-003634241a8fcdec0"
            },
            "us-west-1": {
                "ubuntu18": "ami-0f56279347d2fa43e"
            },
            "us-east-2": {
                "ubuntu18": "ami-07c1207a9d40bc3bd"
            },
            "us-east-1": {
                "ubuntu18": "ami-085925f297f89fce1"
            },
            "ap-south-1": {
                "ubuntu18": "ami-0b44050b2d893d5f7"
            }
        }
    },
    "Resources": {
        "mynetwork": {
            "Type": "AWS::EC2::VPC",
            "Properties": {
                "CidrBlock": "10.10.0.0/16",
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "my network"
                    }
                ]
            }
        },
        "subnet1": {
            "Type": "AWS::EC2::Subnet",
            "Properties": {
                "AvailabilityZone": {
                    "Ref": "subnet1AZ"
                },
                "VpcId": {
                    "Ref": "mynetwork"
                },
                "CidrBlock": "10.10.0.0/24",
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "subnet1"
                    }
                ]
            }
        },
        "subnet2": {
            "Type": "AWS::EC2::Subnet",
            "Properties": {
                "AvailabilityZone": {
                    "Ref": "subnet2AZ"
                },
                "VpcId": {
                    "Ref": "mynetwork"
                },
                "CidrBlock": "10.10.1.0/24",
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "subnet2"
                    }
                ]
            }
        },
        "subnet3": {
            "Type": "AWS::EC2::Subnet",
            "Properties": {
                "AvailabilityZone": {
                    "Ref": "subnet3AZ"
                },
                "VpcId": {
                    "Ref": "mynetwork"
                },
                "CidrBlock": "10.10.2.0/24",
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "subnet2"
                    }
                ]
            }
        },
        "myigw": {
            "Type": "AWS::EC2::InternetGateway",
            "Properties": {
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "myigw"
                    }
                ]
            }
        },
        "AttachGateway": {
            "Type": "AWS::EC2::VPCGatewayAttachment",
            "Properties": {
                "VpcId": {
                    "Ref": "mynetwork"
                },
                "InternetGatewayId": {
                    "Ref": "myigw"
                }
            }
        },
        "myroutetable": {
            "Type": "AWS::EC2::RouteTable",
            "Properties": {
                "VpcId": {
                    "Ref": "mynetwork"
                },
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "my rt"
                    }
                ]
            }
        },
        "routeName": {
            "Type": "AWS::EC2::Route",
            "Properties": {
                "RouteTableId": {
                    "Ref": "myroutetable"
                },
                "DestinationCidrBlock": "0.0.0.0/0",
                "GatewayId": {
                    "Ref": "myigw"
                }
            }
        },
        "routeTableAssocName": {
            "Type": "AWS::EC2::SubnetRouteTableAssociation",
            "Properties": {
                "SubnetId": {
                    "Ref": "subnet1"
                },
                "RouteTableId": {
                    "Ref": "myroutetable"
                }
            }
        },
        "InstanceSecurityGroup": {
            "Type": "AWS::EC2::SecurityGroup",
            "Properties": {
                "GroupDescription": "Allow ssh to client host",
                "VpcId": {
                    "Ref": "mynetwork"
                },
                "SecurityGroupIngress": [
                    {
                        "IpProtocol": "tcp",
                        "FromPort": 22,
                        "ToPort": 22,
                        "CidrIp": "0.0.0.0/0"
                    }
                ]
            }
        },
        "myweb": {
            "Type": "AWS::EC2::Instance",
            "Properties": {
                "KeyName": {
                    "Ref": "keypair"
                },
                "ImageId": {
                    "Fn::FindInMap": [
                        "AMIRegionMap",
                        {
                            "Ref": "AWS::Region"
                        },
                        "ubuntu18"
                    ]
                },
                "InstanceType": {
                    "Ref": "instancetype"
                },
                "NetworkInterfaces": [
                    {
                        "AssociatePublicIpAddress": "true",
                        "DeviceIndex": "0",
                        "GroupSet": [
                            {
                                "Ref": "InstanceSecurityGroup"
                            }
                        ],
                        "SubnetId": {
                            "Ref": "subnet1"
                        }
                    }
                ],
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "myweb"
                    }
                ]
            }
        }
    },
    "Outputs": {
        "publicip": {
            "Value": {
                "Fn::GetAtt": [
                    "myweb",
                    "PublicIp"
                ]
            }
        },
        "privateip": {
            "Value": {
                "Fn::GetAtt": [
                    "myweb",
                    "PrivateIp"
                ]
            }
        }
    }
}

• For the conditions we have a set of functions Refer Here

Scenario

• Write a template to create an vpc ec2 instance and when the user chooses an option to Dev from the environment parameter create an extra ec2 machine and when the user chooses to Test from the environment parameter create an extra subnet
• Look into conditions section, Resources "extraweb" and "subnet" and outputsection

{
    "AWSTemplateFormatVersion": "2010-09-09",
    "Description": "This template is written for learning and it creates s3 bucket and ec2 instance",
    "Parameters": {
        "environment": {
            "Description": "choose",
            "Type": "String",
            "AllowedValues": [
                "Dev",
                "Test"
            ]
        },
        "keypair": {
            "Description": "key pair for ec2 instance",
            "Type": "AWS::EC2::KeyPair::KeyName"
        },
        "instancetype": {
            "Type": "String",
            "AllowedValues": [
                "t2.micro",
                "t2.nano"
            ]
        },
        "subnet1AZ": {
            "Type": "AWS::EC2::AvailabilityZone::Name"
        },
        "subnet2AZ": {
            "Type": "AWS::EC2::AvailabilityZone::Name"
        },
        "subnet3AZ": {
            "Type": "AWS::EC2::AvailabilityZone::Name"
        }
    },
    "Conditions": {
        "CreateDev": {
            "Fn::Equals": [
                {
                    "Ref": "environment"
                },
                "Dev"
            ]
        },
        "CreateTest": {
            "Fn::Equals": [
                {
                    "Ref": "environment"
                },
                "Test"
            ]
        }
    },
    "Mappings": {
        "AMIRegionMap": {
            "us-west-2": {
                "ubuntu18": "ami-003634241a8fcdec0"
            },
            "us-west-1": {
                "ubuntu18": "ami-0f56279347d2fa43e"
            },
            "us-east-2": {
                "ubuntu18": "ami-07c1207a9d40bc3bd"
            },
            "us-east-1": {
                "ubuntu18": "ami-085925f297f89fce1"
            },
            "ap-south-1": {
                "ubuntu18": "ami-0b44050b2d893d5f7"
            }
        }
    },
    "Resources": {
        "mynetwork": {
            "Type": "AWS::EC2::VPC",
            "Properties": {
                "CidrBlock": "10.10.0.0/16",
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "my network"
                    }
                ]
            }
        },
        "subnet1": {
            "Type": "AWS::EC2::Subnet",
            "Properties": {
                "AvailabilityZone": {
                    "Ref": "subnet1AZ"
                },
                "VpcId": {
                    "Ref": "mynetwork"
                },
                "CidrBlock": "10.10.0.0/24",
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "subnet1"
                    }
                ]
            }
        },
        "subnet2": {
            "Type": "AWS::EC2::Subnet",
            "Properties": {
                "AvailabilityZone": {
                    "Ref": "subnet2AZ"
                },
                "VpcId": {
                    "Ref": "mynetwork"
                },
                "CidrBlock": "10.10.1.0/24",
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "subnet2"
                    }
                ]
            }
        },
        "subnet3": {
            "Type": "AWS::EC2::Subnet",
            "Properties": {
                "AvailabilityZone": {
                    "Ref": "subnet3AZ"
                },
                "VpcId": {
                    "Ref": "mynetwork"
                },
                "CidrBlock": "10.10.2.0/24",
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "subnet3"
                    }
                ]
            }
        },
        "subnet4": {
            "Type": "AWS::EC2::Subnet",
            "Condition": "CreateTest",
            "Properties": {
                "AvailabilityZone": {
                    "Ref": "subnet3AZ"
                },
                "VpcId": {
                    "Ref": "mynetwork"
                },
                "CidrBlock": "10.10.2.0/24",
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "subnet4"
                    }
                ]
            }
        },
        "myigw": {
            "Type": "AWS::EC2::InternetGateway",
            "Properties": {
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "myigw"
                    }
                ]
            }
        },
        "AttachGateway": {
            "Type": "AWS::EC2::VPCGatewayAttachment",
            "Properties": {
                "VpcId": {
                    "Ref": "mynetwork"
                },
                "InternetGatewayId": {
                    "Ref": "myigw"
                }
            }
        },
        "myroutetable": {
            "Type": "AWS::EC2::RouteTable",
            "Properties": {
                "VpcId": {
                    "Ref": "mynetwork"
                },
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "my rt"
                    }
                ]
            }
        },
        "routeName": {
            "Type": "AWS::EC2::Route",
            "Properties": {
                "RouteTableId": {
                    "Ref": "myroutetable"
                },
                "DestinationCidrBlock": "0.0.0.0/0",
                "GatewayId": {
                    "Ref": "myigw"
                }
            }
        },
        "routeTableAssocName": {
            "Type": "AWS::EC2::SubnetRouteTableAssociation",
            "Properties": {
                "SubnetId": {
                    "Ref": "subnet1"
                },
                "RouteTableId": {
                    "Ref": "myroutetable"
                }
            }
        },
        "InstanceSecurityGroup": {
            "Type": "AWS::EC2::SecurityGroup",
            "Properties": {
                "GroupDescription": "Allow ssh to client host",
                "VpcId": {
                    "Ref": "mynetwork"
                },
                "SecurityGroupIngress": [
                    {
                        "IpProtocol": "tcp",
                        "FromPort": 22,
                        "ToPort": 22,
                        "CidrIp": "0.0.0.0/0"
                    }
                ]
            }
        },
        "myweb": {
            "Type": "AWS::EC2::Instance",
            "Properties": {
                "KeyName": {
                    "Ref": "keypair"
                },
                "ImageId": {
                    "Fn::FindInMap": [
                        "AMIRegionMap",
                        {
                            "Ref": "AWS::Region"
                        },
                        "ubuntu18"
                    ]
                },
                "InstanceType": {
                    "Ref": "instancetype"
                },
                "NetworkInterfaces": [
                    {
                        "AssociatePublicIpAddress": "true",
                        "DeviceIndex": "0",
                        "GroupSet": [
                            {
                                "Ref": "InstanceSecurityGroup"
                            }
                        ],
                        "SubnetId": {
                            "Ref": "subnet1"
                        }
                    }
                ],
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "myweb"
                    }
                ]
            }
        },
        "extraweb": {
            "Type": "AWS::EC2::Instance",
            "Condition": "CreateDev",
            "Properties": {
                "KeyName": {
                    "Ref": "keypair"
                },
                "ImageId": {
                    "Fn::FindInMap": [
                        "AMIRegionMap",
                        {
                            "Ref": "AWS::Region"
                        },
                        "ubuntu18"
                    ]
                },
                "InstanceType": {
                    "Ref": "instancetype"
                },
                "NetworkInterfaces": [
                    {
                        "AssociatePublicIpAddress": "true",
                        "DeviceIndex": "0",
                        "GroupSet": [
                            {
                                "Ref": "InstanceSecurityGroup"
                            }
                        ],
                        "SubnetId": {
                            "Ref": "subnet1"
                        }
                    }
                ],
                "Tags": [
                    {
                        "Key": "Name",
                        "Value": "myweb"
                    }
                ]
            }
        }
    },
    "Outputs": {
        "publicip": {
            "Value": {
                "Fn::GetAtt": [
                    "myweb",
                    "PublicIp"
                ]
            }
        },
        "privateip": {
            "Value": {
                "Fn::GetAtt": [
                    "myweb",
                    "PrivateIp"
                ]
            }
        },
        
        "publicipextra" : {
          "Value" : {
            "Fn::GetAtt": [
                "extraweb",
                "PublicIp"
            ]
          },
          "Condition": "CreateDev"
        }
        
    }
}