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

14.4 Vertical scaling: changing the instance type

By Ravindra Bagale · Last updated: 25 September 2026

Scale up vs scale out

Think of a busy dosa stall: vertical scaling is buying a bigger tawa for the same cook; horizontal scaling is opening two more counters with more cooks. Technically, vertical scaling moves your EBS-backed instance to different hardware with more resources; horizontal scaling distributes requests across multiple instances via a load balancer.

Steps to change the instance type

Step 1 — Check the current size (on the instance):

nproc          # number of vCPUs
free -h        # RAM
lscpu | grep -E "Model name|Architecture|^CPU\(s\)"

Step 2 — Stop the instance: EC2 → Instances → select → Instance state → Stop instance → wait for Stopped. (Take a snapshot/AMI first if this is important.)

Step 3 — Change type: Actions → Instance settings → Change instance type (the UI may vary slightly) → choose, e.g., t3.small → Apply (or Change). Incompatible types are usually greyed out or rejected with a message.

Step 4 — Start: Instance state → Start instance → note the new public IP (unless you use an Elastic IP) → SSH in again.

Step 5 — Verify:

nproc
free -h
lscpu | grep -E "Model name|Architecture|^CPU\(s\)"
sudo service nginx status        # make sure your apps came back (enabled at boot)

CLI alternative (instance must be stopped):

aws ec2 stop-instances --instance-ids i-0123456789abcdef0
aws ec2 wait instance-stopped --instance-ids i-0123456789abcdef0
aws ec2 modify-instance-attribute --instance-id i-0123456789abcdef0 --instance-type "{\"Value\": \"t3.small\"}"
aws ec2 start-instances --instance-ids i-0123456789abcdef0

What changes and what stays

Compatibility cautions

• Architecture must match: an x86_64 instance (t3, m7i) cannot simply become an Arm/Graviton type (t4g, m7g). The AMI/OS is compiled for one architecture — for Graviton, launch a new instance from an arm64 AMI and migrate.
• Drivers for Nitro types: modern types (t3, m5 and newer) need ENA networking and NVMe storage drivers. Current Amazon Linux, Ubuntu and CentOS Stream AMIs have them; very old AMIs moving from t2 to t3 may fail to boot or lose networking. Also remember disk names change to /dev/nvme... — another reason fstab uses UUIDs (Chapter 13).
• Availability: not every instance type is offered in every AZ/region; the console tells you if a type is unsupported.
• Other features: hibernation, instance store volumes, or placement groups can restrict which types you can switch to.
• Downtime: the stop/start takes a few minutes — plan it in a maintenance window and inform users.