Cloud Computing
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Cloud Computing
Increase AWS EC2 Root Volume Size with Terraform
Increase EC2 root volume size using Terraform root_block_device. Step-by-step guide with complete code, gp3 vs gp2, filesystem resize
LLuca Berton3 min read
The Problem
#Your EC2 instance is running low on disk space. The default root volume is typically 8 GB, which fills up fast with applications, logs, Docker images, or data.
You need to increase it — without destroying and recreating the instance.
Quick Answer
#Add root_block_device to your aws_instance resource:
resource "aws_instance" "web" {
ami = "ami-0c55b159cbfafe1f0"
instance_type = "t3.micro"
root_block_device {
volume_size = 50 # GB (default is 8)
volume_type = "gp3" # General Purpose SSD
encrypted = true
}
}Run terraform apply. Terraform modifies the EBS volume in place — no instance replacement needed.
Complete Example
## variables.tf
variable "root_volume_size" {
description = "Root volume size in GB"
type = number
default = 50
}
variable "root_volume_type" {
description = "EBS volume type"
type = string
default = "gp3"
}
# main.tf
resource "aws_instance" "app" {
ami = data.aws_ami.ubuntu.id
instance_type = "t3.medium"
root_block_device {
volume_size = var.root_volume_size
volume_type = var.root_volume_type
encrypted = true
delete_on_termination = true
tags = {
Name = "app-root-volume"
}
}
tags = {
Name = "app-server"
}
}
data "aws_ami" "ubuntu" {
most_recent = true
owners = ["099720109477"]
filter {
name = "name"
values = ["ubuntu/images/hvm-ssd/ubuntu-jammy-22.04-amd64-server-*"]
}
}
output "root_volume_id" {
value = aws_instance.app.root_block_device[0].volume_id
}Volume Types: gp2 vs gp3 vs io2
#| Type | IOPS | Throughput | Cost | Best For |
|---|---|---|---|---|
| gp3 | 3,000 baseline (up to 16,000) | 125 MB/s (up to 1,000) | $0.08/GB/mo | Most workloads ✅ |
| gp2 | 3 per GB (up to 16,000) | 250 MB/s | $0.10/GB/mo | Legacy (gp3 is better) |
| io2 | Up to 64,000 | 1,000 MB/s | $0.125/GB/mo + IOPS | Databases, high IOPS |
| st1 | 500 | 500 MB/s | $0.045/GB/mo | Throughput-heavy (not for root) |
Always use gp3 unless you have specific IOPS requirements. It's 20% cheaper than gp2 with better baseline performance.
root_block_device {
volume_size = 100
volume_type = "gp3"
iops = 6000 # Optional: increase from 3,000 baseline
throughput = 250 # Optional: increase from 125 MB/s baseline
}What Happens During Resize
#Growing the Volume (e.g., 8 GB → 50 GB)
#- Terraform calls
ModifyVolumeAPI - AWS resizes the EBS volume in place
- Instance stays running — no reboot required for volume modification
- The OS filesystem needs to be extended (see below)
Terraform Plan Output
# # aws_instance.app will be updated in-place
~ resource "aws_instance" "app" {
~ root_block_device {
~ volume_size = 8 -> 50
}
}The key word is in-place — not replaced.
Filesystem Resize (After Terraform Apply)
#The EBS volume is larger, but the OS filesystem still sees the old size. Extend it:
For ext4 (Ubuntu/Debian/Amazon Linux):
# Check current size
df -h /
# Grow the partition (if needed)
sudo growpart /dev/xvda 1
# Extend the filesystem
sudo resize2fs /dev/xvda1For XFS (RHEL/CentOS/Amazon Linux 2023):
sudo growpart /dev/xvda 1
sudo xfs_growfs /NVMe instances (t3, m5, c5, etc.) use /dev/nvme0n1p1:
sudo growpart /dev/nvme0n1 1
sudo resize2fs /dev/nvme0n1p1Automate Filesystem Resize with User Data
#resource "aws_instance" "app" {
ami = data.aws_ami.ubuntu.id
instance_type = "t3.medium"
root_block_device {
volume_size = 50
volume_type = "gp3"
encrypted = true
}
user_data = <<-EOF
#!/bin/bash
# Auto-extend filesystem on boot
growpart /dev/nvme0n1 1 || growpart /dev/xvda 1
resize2fs /dev/nvme0n1p1 || resize2fs /dev/xvda1 || xfs_growfs /
EOF
}Adding Extra EBS Volumes
#For data that should survive instance replacement, use separate EBS volumes:
resource "aws_ebs_volume" "data" {
availability_zone = aws_instance.app.availability_zone
size = 200
type = "gp3"
encrypted = true
tags = {
Name = "app-data-volume"
}
}
resource "aws_volume_attachment" "data" {
device_name = "/dev/xvdf"
volume_id = aws_ebs_volume.data.id
instance_id = aws_instance.app.id
}Then on the instance:
# Format (first time only!)
sudo mkfs -t ext4 /dev/xvdf
# Mount
sudo mkdir -p /data
sudo mount /dev/xvdf /data
# Add to fstab for persistence
echo '/dev/xvdf /data ext4 defaults,nofail 0 2' | sudo tee -a /etc/fstabTroubleshooting
#"volume_size" forces instance replacement
#If changing volume_size shows "must be replaced" instead of "updated in-place", check:
- You're not also changing the AMI
- You're not changing
volume_typefrom the AMI default at the same time - Your Terraform AWS provider version is up to date
Volume modification is slow
#EBS modifications can take 6+ hours for large volumes. Check status:
aws ec2 describe-volumes-modifications --volume-ids vol-12345678Can't shrink a volume
#AWS does not support shrinking EBS volumes. You can only increase the size. To reduce, create a new smaller volume, copy data, and swap.
Filesystem shows old size after resize
#You need to extend the filesystem (see commands above). The EBS volume is larger, but the filesystem needs to be told.
Cost Estimate
#| Size | gp3 Monthly | gp2 Monthly |
|---|---|---|
| 8 GB (default) | $0.64 | $0.80 |
| 20 GB | $1.60 | $2.00 |
| 50 GB | $4.00 | $5.00 |
| 100 GB | $8.00 | $10.00 |
| 500 GB | $40.00 | $50.00 |
Prices for us-east-1. gp3 saves 20% over gp2 at every size.
Hands-On Courses
#Learn by doing with interactive courses on CopyPasteLearn:
Conclusion
#Add root_block_device { volume_size = 50 } to your aws_instance, use gp3 for the volume type, and run terraform apply. The resize happens in place with no instance replacement. Don't forget to extend the filesystem afterward with growpart + resize2fs. For data volumes, use separate aws_ebs_volume resources so they survive instance rebuilds.
#Terraform#AWS#AWS EC2#root block device#storage expansion
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