Deregister old AMIs with boto3

deregister_amis.py

"""
Deregister retired AMIs.

This script deregister all images marked as retired more than a X days
and removes the associated snapshot volumes.
To be able to identify the marked ones as retired and the time when it was
done the following tag system is used:
    - stage [dev|production|retired]: used to track the life cycle of an image.
    - state-changed [YYYYMMDDHHSS]: datetime mark to track when 
                                    stage changes were made.

Code inspired and adapted from the book AWS System Administration
by Mike Ryan and Federico Lucifredi (O’Reilly).
"""
from datetime import datetime

import boto3


DATETIME_FORMAT = "%Y%m%d%H%M"  # TODO: select format from input params with default
DELETE_DELTA = 7 # days TODO: select delta from input params with default

ec2 = boto3.resource("ec2")  # TODO: select region from input params with default

for image in ec2.images.filter(
    Filters=[
        {"Name": "tag:stage", "Values": ["retired"]},
        {"Name": "tag-key", "Values": ["state-changed"]}
    ],
    Owners=["self"]
):
    state_changed = next((tag["Value"] for tag in image.tags if tag["Key"] == "state-changed"))
    state_changed = datetime.strptime(state_changed, DATETIME_FORMAT)
    if (datetime.now()-state_changed).days > DELETE_DELTA:
        devices = image.block_device_mappings
        print(f"Deregistering image {image.id}")
        image.deregister()
        for device in devices:
            if "Ebs" in device:
                snapshot = ec2.Snapshot(device["Ebs"]["SnapshotId"])
                print(f"Deleting snapshot {snapshot.id} for image {image.id}")
                snapshot.delete()
    else:
        print("No image to delete")