Configure cfn-hup, cloudformation tools on ubuntu 18. Based on a gist from https://gist.github.com/kixorz/10194688. Written in YAML.

UbuntuCFinit.yaml

#This script will install the cloudformation helper work on Ubuntu 18.
#Some values are hard coded. Make sure to update where needed, or add to the parameters section.
#This would probably work on other distros, but I have not tested yet. Try it out. 
#Just make sure to change things like apt to yum if trying on another OS.
Parameters:
  EnvironmentSize:
    Type: String
    Default: t3.nano
    AllowedValues:
      - t3.nano
      - t3.small
      - t3.medium
    Description: Select instance size
  #KeyPair section will pull a list of existing keypairs from your account to choose from. Change Default so the intended key is referenced if you are programmatically initiating this build.
  KeyPair:
    Default: somekey
    Description: Existing keypair
    Type: AWS::EC2::KeyPair::KeyName
    
Resources:
#If you change the name of this EC2 instance resource ID from EC2, make sure to update the name throughout the metadata. Anywhere that says EC2 would need to be changed to reflect the new resource instance ID.
  EC2:
    Type: 'AWS::EC2::Instance'
    Properties:
      ImageId: ami-063aa838bd7631e0b
      InstanceType: !Ref EnvironmentSize
      KeyName: !Ref KeyPair
      Tags:
        - Key: Name
          Value: ubuntuCFinit
      UserData:
        Fn::Base64: !Sub |
          #!/bin/bash
          apt-get update -y
          apt-get install -y python-pip
          apt-get install -y python-setuptools
          mkdir -p /opt/aws/bin
          python /usr/lib/python2.7/dist-packages/easy_install.py --script-dir /opt/aws/bin https://s3.amazonaws.com/cloudformation-examples/aws-cfn-bootstrap-latest.tar.gz
          /opt/aws/bin/cfn-init -v --stack ${AWS::StackName} --resource EC2 --configsets setup --region ${AWS::Region}
          /opt/aws/bin/cfn-signal -e --stack ${AWS::StackName} --resource EC2 --configsets setup --region ${AWS::Region}
    Metadata:
    # If you change the configSet ID from setup, ensure you update it throughout the this resource configuration. Anywhere is says setup, change it to reflect the new ID. 
      AWS::CloudFormation::Init:
        configSets:
          setup:
            - "configure_cfn"
        configure_cfn:
          files:
            /etc/cfn/cfn-hup.conf:
              content: !Sub |
                [main]
                stack=${AWS::StackId}
                region=${AWS::Region}
                verbose=true
                interval=5
              mode: "000400"
              owner: root
              group: root
            /etc/cfn/hooks.d/cfn-auto-reloader.conf:
              content: !Sub |
                [cfn-auto-reloader-hook]
                triggers=post.update
                path=Resources.EC2.Metadata.AWS::CloudFormation::Init
                action=/opt/aws/bin/cfn-init -v --stack ${AWS::StackName} --resource EC2 --configsets setup --region ${AWS::Region}
              mode: "000400"
              owner: root
              group: root
            /lib/systemd/system/cfn-hup.service:
              content: !Sub |
                [Unit]
                Description=cfn-hup daemon
                
                [Service]
                Type=simple
                ExecStart=/opt/aws/bin/cfn-hup
                Restart=always
                
                [Install]
                WantedBy=multi-user.target
              mode: "000400"
              owner: root
              group: root
          commands:
            01_enable_cfn-hup:
              command: "systemctl enable cfn-hup.service"
            02_start_cfn-hup:
              command: "systemctl start cfn-hup.service"

Found your response on StackOverflow and it gave me a great starting point. This is the updated user data for Python3:

  UserData:
    Fn::Base64: !Sub |
      #!/bin/bash
      apt-get update -y
      apt-get install -y python3-pip
      pip3 install https://s3.amazonaws.com/cloudformation-examples/aws-cfn-bootstrap-py3-latest.tar.gz
      ln -s /usr/local/init/ubuntu/cfn-hup /etc/init.d/
      /usr/local/bin/cfn-init -v --stack ${AWS::StackName} --resource EC2 --configsets setup --region ${AWS::Region}
      /usr/local/bin/cfn-signal -e $? --stack ${AWS::StackName} --resource EC2 --region ${AWS::Region}