Hold only the last two snapshots

snapshotter.py

#!/usr/bin/env python

import boto3

MAX_SNAPSHOTS = 2   # Number of snapshots to keep

# Create the EC2 resource
ec2 = boto3.resource('ec2')

# Get a list of all volumes
volume_iterator = ec2.volumes.all()

# Create a snapshot of each volume
for v in volume_iterator:
  v.create_snapshot()

  # Too many snapshots?
  snapshots = list(v.snapshots.all())
  if len(snapshots) > MAX_SNAPSHOTS:

    # Delete oldest snapshots, but keep MAX_SNAPSHOTS available
    snap_sorted = sorted([(s.id, s.start_time, s) for s in snapshots], key=lambda k: k[1])
    for s in snap_sorted[:-MAX_SNAPSHOTS]:
      print "Deleting snapshot", s[0]
      s[2].delete()