How to Monitor AWS Network Load Balancer its always run but when its Not working get Alert?

In AWS account Ubuntu EC2 with private Ip and one Network load balancer(need public Ip for that Machine) and open 4 TCP Port in target group (3 show healthy and 1 unhealthy) I know its possible using AWS cloudwatch but which metrics should i used any one port is healthy in target group its show healthy and if all port unhealthy then get alert