s3_iam_maker.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys
import json
import copy
import itertools

base_policy = json.loads("""
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "test",
      "Effect": "Allow",
      "Action": [
        "s3:*"
      ],
      "Resource": []
    }
  ]
}
""")

fresh_policy = lambda: copy.copy(base_policy)

def resources_for_bucket(bucket):
  resources = ["arn:aws:s3:::%(bucket)s", "arn:aws:s3:::%(bucket)s/*"]
  return [ r % { 'bucket': bucket } for r in resources ]

def generate_iam_policy(buckets):
  resources = list(itertools.chain(*[ resources_for_bucket(b) for b in buckets ]))
  policy = fresh_policy()
  policy['Statement'][0]['Resource'] = resources
  return policy

if __name__ == '__main__':
  buckets = sys.argv[1:]

  if not buckets:
    print "Please specify buckets for this policy as arguments."
    print "Ex: %s abc.farmlogs.com www.farmlogs.com" % __file__
    sys.exit()

  policy = generate_iam_policy(buckets)
  print json.dumps(policy, indent=2)