Create an EC2 key pair with ssh-keygen and deploy with AWS CDK

You can create a key pair that will be used to SSH into EC2 instances with:

ssh-keygen -m PEM -b 4096 -f ~/.ssh/my-key-pair -t rsa

This will create two files in ~/.ssh/, one with the private key named my-key-pair and one with the public key named my-key-pair.pub. Parameters:

-m: The key format.
-t: The key type. At the time of this writing on 2023-06-13, EC2 supports RSA and ED25519 keys.
-b: The key bits.
-f: The file name in which the key will be stored. Two files will be generated, one for the private and one for the public key.

You can use the public key to create an EC2 key pair and associate it with your EC2 instances. Here's a minimal CDK code snippet for this:

import { Stack, StackProps } from 'aws-cdk-lib';
import * as ec2 from 'aws-cdk-lib/aws-ec2';
import { Construct } from 'constructs';

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

    const cfnKeyPair = new ec2.CfnKeyPair(this, 'MyCfnKeyPair', {
      keyName: 'keyName',
      publicKeyMaterial: [
        'ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAACAQCtS/sY98Yk6RqJXrWQIqMrRoesRKTI0s6xRUlSPJzx7G8kbWKEH1YS+kE0xFOfdbo/MpXpU',
        'yFf9vTIKS5HEG5ZKhFnLpbh3fBBfFmkFNazJcxpyu4yGQyy8SEhavM8xMl1NCpIhBmg8fccn78FwHVjrwBDaXlLkCkHkQf5AM+Fgx2lEOuSNz',
        '4NmIvDBAEzJi8gixgKlZM5wnyEOHXyUQ04Xs+vS6RHLxmBQ90ncmMga9FhflqfmSC8r/1uMVQYgW+8/pXOGvbMRmdy9zxxnIz6EBcNtAyWhGO',
        'sWB743fdXpCpbIqtiMXImkpjnItU15ar9ij+vkgB5nKBBqFbIvlQ0IKYZ5VJxZMFlpRNZAVyEDedcDWSvc8As5APYau/UgdEv73ingEZpqZR5',
        'VcpKQfP4F3psgHtIO+cyPvKss0Q0vKPMwmpl7z5RRcbKxWGXizsQ+B9kvVs3HzK8gu4qaDW1RbEyWkdIzOkV+ovnhqzbn9o6078hkdIU62wix',
        'k7fI9ugiOEFLoTiiAUo2H/nQ+Z06I+rxrOgF3ucGpBmAm6VaIO0upjysbKL+g05WRj5BKsHp2a2DfMlzp+TcDbpMcy/4YXYwA+BGIilIKeFbR',
        'AkWDT6MP/mLfh0ud4+xZpdymS1Qvq4AzasRVQatVWZpaVWOpGzjF5KJkzhWz4DHAnL5Q== m@e'
      ].join('')
    });
  }
}

References:

CfnKeyPair (construct) in the CDK documentation.
Amazon EC2 key pairs and Linux instances in the EC2 user guide.

Image credit: Kylemore Abbey, by Lode Van de Velde. In the Public Domain. Source.