How do EBS snapshots work and how can you use them to move data to another AZ or Region?
A snapshot is a point-in-time backup of an EBS volume, stored in S3-managed storage. After the first full copy, later snapshots are incremental. You can create a new volume from a snapshot in any AZ of the Region, or copy the snapshot to another Region.
Explain it simply
A snapshot is like photographing a whiteboard before wiping it. The first photo captures everything. Later photos record only what changed since the last one, but each photo can still rebuild the whole board.
Example
# Take a snapshot
aws ec2 create-snapshot --volume-id vol-0abc --description "db-nightly"
# Recreate a volume in a different AZ
aws ec2 create-volume --snapshot-id snap-0123 \
--availability-zone ap-south-1b
# Copy the snapshot to another Region (run against the destination)
aws ec2 copy-snapshot --source-region ap-south-1 \
--source-snapshot-id snap-0123 --region ap-southeast-1An EBS volume lives in one AZ and attaches only to instances in that AZ. Snapshots are the way out: they are Regional, so a volume made from one can go to any AZ there, and a copy can cross Regions for disaster recovery.
Deleting an older snapshot never breaks newer ones, because AWS keeps the data blocks that later snapshots still need. Automate schedules with Amazon Data Lifecycle Manager or AWS Backup.
What to say in the interview
"Snapshots are incremental, point-in-time backups kept in S3-managed storage. Since volumes are tied to an AZ, I restore from a snapshot into another AZ, or copy it to another Region for DR. I schedule them with Data Lifecycle Manager or AWS Backup."
Common mistakes
- Thinking an EBS volume can be attached across AZs directly.