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Chapter 14: EC2 Operations — Elastic IP, AMI, Snapshots and Vertical Scaling

Interview Questions

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Q1. What is an Elastic IP and why is it needed?
A static public IPv4 address owned by your account. The auto-assigned public IP changes on stop/start; an EIP stays the same and can be moved between instances, so DNS records don't need to change.
Q2. How would you replace a web server without changing DNS?
Build and test the new instance, then re-associate the Elastic IP from the old instance to the new one (allow reassociation). Traffic switches within seconds; keep the old instance briefly for rollback.
Q3. What does an AMI consist of?
One or more EBS snapshots (root and optionally data volumes), a block device mapping, launch permissions and metadata such as architecture and virtualization type.
Q4. What is the risk of the "No reboot" option when creating an AMI?
The filesystem is captured while running, so in-flight writes may not be flushed and the image may be inconsistent (crash-consistent); databases might need recovery.
Q5. Are EBS snapshots full or incremental? Where are they stored?
Incremental — only changed blocks after the first snapshot. They are stored in Amazon S3, managed by AWS (not visible in your buckets), and are regional.
Q6. How do you restore a single deleted file from an EBS snapshot?
Create a volume from the snapshot in the instance's AZ, attach it, mount it read-only (with nouuid for XFS on the same instance), copy the file back, then unmount, detach and delete the temporary volume.
Q7. How do you automate EBS snapshots?
Use Amazon Data Lifecycle Manager (tag-based policies with schedules and retention) or AWS Backup.
Q8. What is the difference between vertical and horizontal scaling? What changes when you change an instance type?
Vertical = bigger instance (needs stop/start); horizontal = more instances behind a load balancer (ASG + ELB). After a type change, the auto-assigned public IP changes (unless EIP) and instance store data is lost; EBS data, private IP and instance ID stay.