I frequently ran out of time when I have a packer debug session open and the saml role only grant me one hour of access. So instead of manually removing the keypair and the security group, I come up with this script.

packer_cleanup.py

#!/usr/bin/env python
# encoding=utf8
"""
This script will cleanup leftover resources(instance, key-pair and security group)
related to an instance specified by its ipaddr or instance-id.

I frequently ran out of time when I have a packer debug session open and
the saml role only grant me one hour of access. So instead of manually 
removing the keypair and the security group, I come up with this script.
"""
from __future__ import print_function

import sys
import time

import boto3


def get_instance(spec):
    """Get packer build instance.

    The instance can be specified by its id, private_ip_address or
    public_ip_address.
    """
    boto3.setup_default_session(region_name='ap-southeast-2')
    ec2 = boto3.resource('ec2')
    instances = ec2.instances.filter(
        Filters=[{
            'Name': 'instance-state-name', 'Values': [
                'running', 'stopped', 'terminated'
            ],
        }]
    )

    for inst in instances:
        print(inst.id, inst.private_ip_address)
        candidates = [
            inst.id, inst.private_ip_address, inst.public_ip_address,
        ]
        if spec in candidates:
            return inst
    else:
        raise RuntimeError("Instance not found!")

def cleanup(instance):
    """Cleanup resources used by an instance.

    This will verify that this is the right instance, then it will do the
    following cleanups:
      * remove the keypair created by packer
      * terminate the instance
      * remove the security group attached to the instance.
    """
    # Verify we've got the right instance.
    assert instance.key_pair.name.startswith('packer_')

    # Print out some info about the instance
    print("About to terminate this instance /w its resources:")
    print("Instance ID: {}".format(instance.id))
    print("Internal IPaddr: {}".format(instance.private_ip_address))
    print("SecurityGroup: {}".format(instance.security_groups))
    print("Key Pair: {}".format(instance.key_pair.key_name))

    # remove the keypair first
    instance.key_pair.delete()

    # terminate the instance so we can delete the security group.
    print("Terminating the instance.", end="")
    while True:
        response = instance.terminate()
        status = response['TerminatingInstances'][0]['CurrentState']['Name']
        if status == 'terminated':
            print("\nInstance terminated.")
            break
        time.sleep(2)
        print(".", end='')

    # and finally, remove the security group.
    # FIXME: could add a try-except block here.
    if instance.security_groups:
        instance.security_groups[0].delete()
    print("Resources cleaned.")


def main():
    instance = get_instance(sys.argv[1])
    cleanup(instance)

if __name__ == '__main__':
    main()