EC2 instances unhealthy when created via ASG using cdk.

I am creating an ASG which will have a classical load balancer . The desired number of instances is 5 , I am starting the asg creation using a userdata but even after experimenting multiple times the load balancer shows unhealthy hosts,i changed the subnet type of the vpc as public but the number of healthy host for the elb remains 0 . Below is the code segment

 Vpc vpc=new Vpc(this,"MyVPC");
        AutoScalingGroup asg = AutoScalingGroup.Builder.create(this,"AutoScalingGroup").vpcSubnets(SubnetSelection.builder()
                        .subnetType(SubnetType.PUBLIC)
                        .build()).vpc(vpc).instanceType(InstanceType.of(InstanceClass.BURSTABLE2, InstanceSize.MICRO))
                .machineImage(new AmazonLinuxImage()).minCapacity(1).desiredCapacity(5).maxCapacity(10).build();
        asg.addUserData("#!/bin/bash\n" +
                "# Use this for your user data (script from top to bottom)\n" +
                "# install httpd (Linux 2 version)\n" +
                "yum update -y\n" +
                "yum install -y httpd\n" +
                "systemctl start httpd\n" +
                "systemctl enable httpd\n" +
                "echo \"<h1>Hello World from $(hostname -f)</h1>\" > /var/www/html/index.html");
        LoadBalancer loadbalancer=LoadBalancer.Builder.create(this,"ElasticLoadBalancer").vpc(vpc).internetFacing(Boolean.TRUE).healthCheck(software.amazon.awscdk.services.elasticloadbalancing.HealthCheck.builder().port(80).build())
                .build();
        loadbalancer.addTarget(asg);
        ListenerPort listenerPort = loadbalancer.addListener(LoadBalancerListener.builder().externalPort(80).build());

Also the instances those are created by default via ASG cannot be accessed on the web(by hitting their public IP) even after changing the security groups or making them all in a public subnet they are not accessible from instance connect,neither the load balancer shows these hosts healthy