ec2: userData in launchTemplate is not created automatically even when machineImege is provided

[tmokmss]

Describe the bug

Reading this doc, userData is expected to be automatically created when machineImage is provided.

(optional, default: This Launch Template creates a UserData based on the type of provided machineImage; no UserData is created if a machineImage is not provided)

However, it is not working as expected; userData is not automatically created at all. See reproduction steps for the actual code.

Expected Behavior

userData is automatically created when machineImage is provided.

Current Behavior

userData is not created even when machineImage is provided.

Reproduction Steps

Synthesize the below stack:

export class Ec2UserdataStack extends cdk.Stack {
  constructor(scope: Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    const launchTemplate = new ec2.LaunchTemplate(this, 'LaunchTemplate', {
      instanceType: new ec2.InstanceType('t3.small'),
      machineImage: new ec2.AmazonLinuxImage({
        generation: ec2.AmazonLinuxGeneration.AMAZON_LINUX_2,
      }),
    });

    // this will cause an error
    launchTemplate.userData!.addCommands("yum -y update")
  }
}

and we get the following error:

/../ec2-userdata/lib/ec2-userdata-stack.ts:26
    launchTemplate.userData!.addCommands("yum -y update")
                             ^
TypeError: Cannot read properties of undefined (reading 'addCommands')

Possible Solution

Current implementation is here. We need to add code for creating userData depending on machineImage.

I guess we can follow the below implementation in ec2.Instance:

aws-cdk/packages/@aws-cdk/aws-ec2/lib/instance.ts

Lines 349 to 351 in f178c98

	// use delayed evaluation
	const imageConfig = props.machineImage.getImage(this);
	this.userData = props.userData ?? imageConfig.userData;

Additional Information/Context

Adding this feature will not be a breaking change because we are just adding empty userData to launchTemplates whose userData was not specified explicitly, and it will not have any effect on the existing behavior.

CDK CLI Version

2.59.0

Framework Version

2.59.0

Node.js Version

v16.18.1

OS

macOS

Language

Typescript

Language Version

No response

Other information

No response

[peterwoodworth]

Thanks for the quick PR on this!

[github-actions]

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