David A Good

How to Specify AWS EC2 Root Volume Size with CDK

May 12, 2021

Here’s how to override the size of the root volume on your AWS EC2 instance using CDK. Not at all obvious!

Step 1: Check The Root Device Name

Update this command with your region and AMI:

aws ec2 describe-images --region us-east-1 --image-ids ami-0d5eff06f840b45e9

In this example output from the describe-images command, the device name is "/dev/xvda". The property path is .Images[0].BlockDeviceMappings[0].DeviceName.

  "Images": [
      "Architecture": "x86_64",
      "CreationDate": "2021-04-29T10:14:01.000Z",
      "ImageId": "ami-0d5eff06f840b45e9",
      "ImageLocation": "amazon/amzn2-ami-hvm-2.0.20210427.0-x86_64-gp2",
      "ImageType": "machine",
      "Public": true,
      "OwnerId": "137112412989",
      "PlatformDetails": "Linux/UNIX",
      "UsageOperation": "RunInstances",
      "State": "available",
      "BlockDeviceMappings": [
          "DeviceName": "/dev/xvda",
          "Ebs": {
            "DeleteOnTermination": true,
            "SnapshotId": "snap-01047646ec075f543",
            "VolumeSize": 8,
            "VolumeType": "gp2",
            "Encrypted": false
      "Description": "Amazon Linux 2 AMI 2.0.20210427.0 x86_64 HVM gp2",
      "EnaSupport": true,
      "Hypervisor": "xen",
      "ImageOwnerAlias": "amazon",
      "Name": "amzn2-ami-hvm-2.0.20210427.0-x86_64-gp2",
      "RootDeviceName": "/dev/xvda",
      "RootDeviceType": "ebs",
      "SriovNetSupport": "simple",
      "VirtualizationType": "hvm"

Step 2: Use the Root Device Name When Constructing the EC2 Instance

Now build an BlockDevice using the root device name from Step 1. Then provide the root block device on the blockDevices property when constructing the EC2 instance.

import * as cdk from '@aws-cdk/core';
import * as ec2 from '@aws-cdk/aws-ec2';

export class Ec2Stack extends cdk.Stack {
  constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    // Other setup

    const rootVolume: ec2.BlockDevice = {
      deviceName: '/dev/xvda', // Use the root device name from Step 1
      volume: ec2.BlockDeviceVolume.ebs(50), // Override the volume size in Gibibytes (GiB)

    const instance = new ec2.Instance(this, `${name}-ec2-instance`, {
      // Other properties
      blockDevices: [rootVolume],



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