You can use CloudWatch which is already part of EC2 to monitor your instances for you. You can also have autoscaling scale up / down based on these metrics. You

You can use CloudWatch which is already part of EC2 to monitor your instances for you. You can also have autoscaling scale up / down based on these metrics. You also can have Elastic Load Balancer monitor the health of your backend web hosts port state (ie: is the nginx port down for more than three health checks? OK kill that instance and replace it with a new one behind the ELB). All of these functions are builtin to AWS and now with the new web interface it is much easier to configure autoscaling to do these types of things.