AWS CDK - Linux EC2 Instance Cloudformation Init - /opt/aws/bin/cfn-signal doesn't run properly after reboot

Question

So I'm trying to bootstrap my linux ec2 instance via cloudformation. What I want to do is to:

1. change hostname
2. reboot
3. send complete signal

so I have here an aws cdk python code:

testInit = ec2.CloudFormationInit.from_config_sets(

        config_sets={

            "test_configsets" : ["change_hostname", "reboot", "cfn-signal"]
        },

        configs={

            "change_hostname" : ec2.InitConfig([

                ec2.InitCommand.shell_command("> /etc/hostname ; echo testInstance > /etc/hostname", key = "change_hostname")

            ]),

            "reboot" : ec2.InitConfig([

                ec2.InitCommand.shell_command("reboot", key = "reboot")
            ]),

            "cfn-signal" : ec2.InitConfig([

                ec2.InitCommand.shell_command(core.Fn.sub("/opt/aws/bin/cfn-signal -e 0 --stack ${AWS::StackId} --resource TestInstance --region ${AWS::Region}"), key = "signal_complete")
            ])
        
        }

    )

Since the reboot will cause the cfn-signal on the user data section to not run, I've placed the cfn-signal on the AWS::CloudFormation::Init metadata section instead after the reboot command hoping that it will send success signal after the reboot. I tried this method on Windows Instance and it's working perfectly (https://aws.amazon.com/premiumsupport/knowledge-center/create-complete-bootstrapping/)

The change_hostname and reboot command runs sucessfully but then it got stuck indefinitely at the cfn-signal command and eventually the stack fails to create because of the time out. I tried to run the cfn-signal via ssh to the instance and it works just fine.

when I echo the command block of cfn_signal the Cloudformation pseudo parameters reference resolves perfectly fine as well.

This is the cdk synth output of the related code block

Metadata:
  aws:cdk:path: cdk-ec2/TestInstance/Resource
  AWS::CloudFormation::Init:
    configSets:
      test_configsets:
        - change_hostname
        - reboot
        - cfn-signal
    change_hostname:
      commands:
        change_hostname:
          command: "> /etc/hostname ; echo testInstance > /etc/hostname"
    reboot:
      commands:
        reboot:
          command: reboot
    cfn-signal:
      commands:
        signal_complete:
          command:
            Fn::Sub: /opt/aws/bin/cfn-signal -e 0 --stack ${AWS::StackId} --resource TestInstance --region ${AWS::Region}

This is the output of /var/log/cfn-init.log

[INFO] Running config cfn-signal

[DEBUG] No packages specified

[DEBUG] No groups specified

[DEBUG] No users specified

[DEBUG] No sources specified

[DEBUG] No files specified

[DEBUG] Running command signal_complete

[DEBUG] No test for command signal_complete

Appreciate any help !

Thanks, Sheldon