EC2 User Data Example in AWS CDK - Complete Guide

Adding User Data to an EC2 Instance in AWS CDK #

User data allows us to add commands to the startup script of an EC2 instance.

In order to add user data to an EC2 instance, we have to load the script from the local file system and pass it to the addUserData method on the instance.

lib/cdk-starter-stack.ts

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import {readFileSync} from 'fs';

// 👇 load user data script
const userDataScript = readFileSync('./lib/user-data.sh', 'utf8');
// 👇 add user data to the EC2 instance
ec2Instance.addUserData(userDataScript);

In this article we're going to look at a complete example of creating an EC2 instance and adding user data to it. Our user data script installs and starts an apache web server.

The code for this article is available on GitHub

Let's look at the code for the complete example:

lib/cdk-starter-stack.ts

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import * as ec2 from 'aws-cdk-lib/aws-ec2';
import * as cdk from 'aws-cdk-lib';
import {readFileSync} from 'fs';

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

    // 👇 import default VPC
    const vpc = ec2.Vpc.fromLookup(this, 'my-default-vpc', {
      isDefault: true,
    });

    // 👇 create a security group for the EC2 instance
    const webserverSG = new ec2.SecurityGroup(this, 'webserver-sg', {
      vpc,
    });

    webserverSG.addIngressRule(
      ec2.Peer.anyIpv4(),
      ec2.Port.tcp(80),
      'allow HTTP traffic from anywhere',
    );

    // 👇 create the EC2 instance
    const ec2Instance = new ec2.Instance(this, 'ec2-instance', {
      vpc,
      vpcSubnets: {
        subnetType: ec2.SubnetType.PUBLIC,
      },
      securityGroup: webserverSG,
      instanceType: ec2.InstanceType.of(
        ec2.InstanceClass.BURSTABLE2,
        ec2.InstanceSize.MICRO,
      ),
      machineImage: new ec2.AmazonLinuxImage({
        generation: ec2.AmazonLinuxGeneration.AMAZON_LINUX_2,
      }),
    });

    // 👇 load user data script
    const userDataScript = readFileSync('./lib/user-data.sh', 'utf8');

    // 👇 add user data to the EC2 instance
    ec2Instance.addUserData(userDataScript);
  }
}

If you still use CDK version 1, switch to the cdk-v1 branch in the GitHub repository.

Let's go over the code snippet.

We imported the default VPC, in which we'll launch the EC2 instance
We created a security group with the following inbound rule:

Type	Protocol	Port	Source
HTTP	TCP	80	`0.0.0.0/0`

We allowed inbound HTTP traffic on port 80 from anywhere. Note that by default all outbound traffic is allowed.

We created a t2.micro EC2 instance with AMAZON LINUX 2 AMI. The instance is launched in a public subnet of our VPC because we'll use it as a web server.
We loaded the user data script from the file system and passed it in a call to the addUserData method on the instance.

The code for this article is available on GitHub

Let's add the user data script, which installs and starts an apache web server, at lib/user-data.sh:

lib/user-data.sh

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#!/bin/bash

sudo su
yum update -y
yum install -y httpd

systemctl start httpd
systemctl enable httpd

echo "<h1>Hello World from $(hostname -f)</h1>" > /var/www/html/index.html

The script installs and starts the apache webserver.

If our user data script works as intended, our web server should respond with a simple "Hello World" message, when we paste the instance's public IPv4 address in our web browser.

Next, we'll deploy and test our user data script.