Starting today, you can configure EC2 Fleet and Spot Fleet to automatically terminate a Spot Instance when using Capacity Rebalancing. With Capacity Rebalancing, EC2 Fleet and Spot Fleet attempt to replace a Spot Instance when it is at an elevated risk of interruption as indicated by the EC2 Instance rebalance recommendation signal. Until now, EC2 Fleet or Spot Fleet launched a replacement Spot Instance without terminating the Spot Instance that received a rebalance recommendation, meaning you needed to either manually terminate the instance once workload rebalancing was completed, or let the instance run until it was interrupted by EC2. Now, you can set up EC2 Fleet or Spot Fleet to automatically terminate the instance that receives a rebalance recommendation with a specified termination delay.
Source:: Amazon AWS