(ec2): using ARM-based instances in BastionHostLinux results in an invalid instance configuration

[Jacob-Doetsch]

Deployment of a stack containing a BastionHostLinux construct backed by an ARM-based instance (e.g., a1, t4g, etc) will fail, with CloudFormation reporting the following for the EC2 instance resource:

't4g.nano' is not a valid instance type for instance 'i-*********' of architecture 'x86_64'. (Service: AmazonEC2; Status Code: 400; Error Code: InvalidInstanceAttributeValue; Request ID: ********; Proxy: null)

Reproduction Steps

The following stack will fail during deployment:

const cdk = require('@aws-cdk/core');
const ec2 = require('@aws-cdk/aws-ec2');
class BastionHostReproStack extends cdk.Stack {

  constructor(scope, id, props) {
    super(scope, id, props);

    this.vpc = new ec2.Vpc(this, 'Vpc');
    new ec2.BastionHostLinux(this, 'BastionHost', {
      vpc: this.vpc,
      instanceType: ec2.InstanceType.of(ec2.InstanceClass.T4G, ec2.InstanceSize.NANO),
    });
  }
}

module.exports = { BastionHostReproStack }

What did you expect to happen?

The stack should deploy successfully when using an instanceType on BastionHostLinux that has an InstanceClass with an ARM architecture.

What actually happened?

CloudFormation will report the following for the backing EC2 instance:

't4g.nano' is not a valid instance type for instance 'i-*********' of architecture 'x86_64'. (Service: AmazonEC2; Status Code: 400; Error Code: InvalidInstanceAttributeValue; Request ID: ********; Proxy: null)

Environment

• CDK CLI Version : 1.80
• Framework Version: 1.80
• Node.js Version: 15.2.1
• OS : Ubuntu (WSL2)
• Language (Version): TypeScript, JavaScript

Other

In the constructor of BastionHostLinux, the architecture of the instanceType is assumed to be x86-64, and so the Amazon Linux 2 X86-64 AMI is always used for the backing EC2 instance even if the instanceType uses an instance class that is ARM-based. This explains the error reported by CloudFormation.
Furthermore, only the x86-64 SSM Agent rpm is installed via UserData.

Proposed fix at #12280

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This is 🐛 Bug Report

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