Autoscaling group instances not register on ALB

I have the following Cloudformation template, but the instances are only up for a few seconds before resulting in terminate status.

I thought it had something to do with the 'grace' period, 'timeout' periods, but still haven't been able to figure it out.

Basically, this template is to create autoscaling groups (target group) with multiple instances and register on the ALB.

How do I fix this issue and what's the best way to debug?

AWSTemplateFormatVersion: 2010-09-09
Description: ec2-instance
  
Parameters:
  # Azs:
  #   Description: Avialbility zones
  #   Type: String
  #   Default: ap-southeast-2a

  AMIs:
    Description: AMIs
    Type: String
    Default: Linux
    AllowedValues:
      - Linux
      - Windows
  
  InstanceCount:
    Description: Number of instances
    Type: Number
    Default: 1

  Environment:
    Description: Hosting Environment
    Type: String
    Default: Dev
    AllowedValues:
      - Dev
      - Prod

  Subnet01:
    Description: Subnet1
    Type: String
    Default: 10.0.1.0/24

  Subnet02:
    Description: Subnet2
    Type: String
    Default: 10.0.2.0/24
    
  LaunchTemplateVersionNumber:
    Default: 1
    Type: String
# Metadata:
  
Mappings:
  FreeTier:
    Linux:
      HVM64: ami-0d9f286195031c3d9
    Windows:
      HVM64: ami-09cf24ffd6d332930

Conditions:
  SelectImage: !Equals [!Ref AMIs, Linux]
  SelectEnv: !Equals [ !Ref Environment, Dev]
  
# Transform:
  
Resources:
  
  ApplicationLB:
    Type: AWS::ElasticLoadBalancingV2::LoadBalancer
    Properties:
      Type: application
      IpAddressType: ipv4
      Scheme: internet-facing
      Subnets:
        - !Ref MySubnet01
        - !Ref MySubnet02 
      Name: WebAppLB
      SecurityGroups: 
        - !Ref SecurityALB
      
      
  
  ALBListner:
    Type: AWS::ElasticLoadBalancingV2::Listener
    Properties:
      LoadBalancerArn: !Ref ApplicationLB
      DefaultActions:
        - Type: forward
          TargetGroupArn: !Ref MyTargetGroup
      Port: 80
      Protocol: "HTTP"
  
  MyTargetGroup:
    Type: AWS::ElasticLoadBalancingV2::TargetGroup
    Properties:
      HealthCheckEnabled: true
      HealthCheckIntervalSeconds: 30
      HealthCheckPath: /index.html
      HealthCheckPort: 80
      Port: 80
      Protocol: HTTP
      VpcId: !Ref MyVpc
      TargetType: "instance"
      Matcher: 
        HttpCode: "200"
      TargetGroupAttributes:
        - Key: load_balancing.algorithm.type
          Value: round_robin
        - Key: "deregistration_delay.timeout_seconds"
          Value: "3000"
        

  MyVpc:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: 10.0.0.0/16
      EnableDnsHostnames: true
      EnableDnsSupport: true

  MySubnet01:
    Type: AWS::EC2::Subnet
    Properties:
      AvailabilityZone:
        Fn::Select:
          - 0
          - Fn::GetAZs:
              Ref: AWS::Region
      CidrBlock: !Ref Subnet01
      VpcId: !Ref MyVpc
  
  MySubnet02:
    Type: AWS::EC2::Subnet
    Properties:
      AvailabilityZone:
        Fn::Select:
          - 1
          - Fn::GetAZs:
              Ref: AWS::Region
      CidrBlock: !Ref Subnet02 
      VpcId: !Ref MyVpc
  
  MyRouteTable:
    Type: AWS::EC2::RouteTable
    Properties:
      VpcId: !Ref MyVpc

  MyIgw:
    Type: AWS::EC2::InternetGateway
  
  Subnet01RouteTableAssociation:
    Type: AWS::EC2::SubnetRouteTableAssociation
    Properties:
      SubnetId: !Ref MySubnet01
      RouteTableId: !Ref MyRouteTable

  Subnet02RouteTableAssociation:
    Type: AWS::EC2::SubnetRouteTableAssociation
    Properties:
      SubnetId: !Ref MySubnet02
      RouteTableId: !Ref MyRouteTable
  
  VPCGatewayAttachment:
    Type: AWS::EC2::VPCGatewayAttachment
    Properties:
      InternetGatewayId: !Ref MyIgw
      VpcId: !Ref MyVpc

  Route: 
    DependsOn: VPCGatewayAttachment
    Type: AWS::EC2::Route
    Properties:
      RouteTableId: !Ref MyRouteTable 
      DestinationCidrBlock: 0.0.0.0/0
      GatewayId: !Ref MyIgw

  Launchtemplate:
    Type: AWS::EC2::LaunchTemplate
    Properties:
      LaunchTemplateData:
        ImageId: !If [SelectImage, !FindInMap [ FreeTier, Linux, HVM64 ], !FindInMap [ FreeTier, Windows, HVM64 ]]  
        InstanceType: t2.micro
        KeyName: cfn-putty
        UserData: 
          Fn::Base64: |
            #!/bin/bash
            sudo yum -y install httpd
            sudo touch /var/www/html/index.html
            echo "webserver v1" > /var/www/html/index.html
            sudo hostname >> /var/www/html/index.html
            sudo ifconfig >> /var/www/html/index.html
            systemctl start httpd.service
        
        SecurityGroups:
          - !Ref enbalessh


  LauncConfig:
    Type:  AWS::AutoScaling::AutoScalingGroup
    Properties:
      DefaultInstanceWarmup: 60
      HealthCheckGracePeriod: 120
      HealthCheckType: ELB
      AvailabilityZones:
        Fn::GetAZs:
          Ref: "AWS::Region"
      MaxSize: 3
      MinSize: 1
      TargetGroupARNs: 
        - !Ref  MyTargetGroup
      DesiredCapacity: !Ref InstanceCount
      LaunchTemplate:
        LaunchTemplateId: !Ref Launchtemplate
        Version: !Ref LaunchTemplateVersionNumber
      Tags:
        - Key: "Environment"
          PropagateAtLaunch: true
          Value: !If [SelectEnv,Dev,Prod]
        - Key: "Name"
          PropagateAtLaunch: true
          Value: !Sub 
            - "web-${os}-${env}"
            - os: !Ref AMIs
              env: !Ref Environment
                     
              
  enbalessh:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: enable-ssh
      SecurityGroupIngress:
        - IpProtocol: tcp
          FromPort: '22'
          ToPort: '22'
          CidrIp: "0.0.0.0/0"  
        - IpProtocol: tcp
          FromPort: 80
          ToPort: 80
          CidrIp: "0.0.0.0/0"

  SecurityALB:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: Incoming-traffic-lb
      SecurityGroupIngress:
        - IpProtocol: tcp
          FromPort: '80'
          ToPort: '80'
          CidrIp: "0.0.0.0/0"
      VpcId: !Ref MyVpc  

Probably because you are creating instances and its associated security groups in a default VPC, white your ALB is in your custom VPC.

So to fix that both instances and ALB must be in same VPC. You can't join them across VPCs without a VPC peering connection.