Spot instances are the spare EC2 capacity that helps the user to save up 90% off of On-Demand prices that AWS can interrupt with a 2-minute notification. Spot uses the almost similar underlying EC2 instances as the On-Demand and Reserved Instances, and can be the best suited for fault-tolerant scenarios and flexible workloads. Spot instances provides an additional option that can be used for obtaining compute capacity and also can be used along with the On-Demand and the Reserved Instances.