Use boto3 to generate an ssh config file entry for all your running instances (checks to see if you've already added them as well).

ssh.py

import os
import boto3

if __name__ == '__main__':
    session = boto3.Session()
    ec2 = session.resource('ec2')
    ec2c = session.client('ec2')
    # add active instances to the user's ssh config file
    instances = ec2.instances.filter(
                Filters=[{'Name': 'instance-state-name', 'Values': ['running']}])
    config = []
    try:
        config_path = os.path.join(os.environ['HOME'],".ssh/config")
        with open(config_path, "r") as f:
            old_config = f.read()
    except FileNotFoundError:
        old_config = ""
    for instance in instances:
        name = instance.tags[0]["Value"]
        if name not in old_config:
            config.append("# Generated for EC2 #")
            config.append(f'Host {name}')
            config.append(f'    HostName {instance.public_ip_address}')
            config.append(f'    User ubuntu')
            config.append(f'    IdentityFile ~/.ssh/{instance.key_name}.pem')
            config.append("# End Generated #")
    print("\n".join(config))