AWS Certification tips:

How to encrypt root device volumes?

root device volumes are basic an EBS volumes, where Operating system is installed.

Converting EBS volumes from not encrypted to encrypted:

•  provision an EC2 instance.
• take snapshot for the root volume.
•  copy the snapshot, while coping make it as encrypt.
• Provision a AMI with the encrypted snapshot copy.
• Launch EC2 instance with the above encrypted AMI image.

• for EBS volumes & for instance store volumes
• Spot instances and Spot Fleets
  
• EC2 placement groups