lambda.py

'''
Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
Licensed under the Apache License, Version 2.0 (the "License"). You may not use this file except in compliance with the License. A copy of the License is located at
    http://aws.amazon.com/apache2.0/
or in the "license" file accompanying this file. This file is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
'''

import boto3
import hashlib
import json
import urllib2

# Name of the service, as seen in the ip-groups.json file, to extract information for
SERVICE = "CLOUDFRONT"

# Ports your application uses that need inbound permissions from the service for
INGRESS_PORTS = {'Https': 443}

# Security GroupIds which identify the security groups you want to update with global Ips
GLOBAL_SECURITY_GROUP_IDS = [
    'sg-########',
    'sg-########'
]

# Security GroupIds which identify the security groups you want to update with regional Ips
REGIONAL_SECURITY_GROUP_IDS = [
    'sg-########',
    'sg-########'
]


def lambda_handler(event, context):
    print("Received event: " + json.dumps(event, indent=2))
    message = json.loads(event['Records'][0]['Sns']['Message'])

    # Load the ip ranges from the url
    ip_ranges = json.loads(get_ip_groups_json(message['url'], message['md5']))

    # extract the service ranges
    global_cf_ranges = get_ranges_for_service(ip_ranges, SERVICE, "GLOBAL")
    region_cf_ranges = get_ranges_for_service(ip_ranges, SERVICE, "REGION")
    ip_ranges = {"GLOBAL": global_cf_ranges, "REGION": region_cf_ranges}

    # update the security groups
    result = update_security_groups(ip_ranges)

    return result


def get_ip_groups_json(url, expected_hash):
    print("Updating from " + url)

    response = urllib2.urlopen(url)
    ip_json = response.read()

    m = hashlib.md5()
    m.update(ip_json)
    hash = m.hexdigest()

    if hash != expected_hash:
        raise Exception('MD5 Mismatch: got ' + hash + ' expected ' + expected_hash)

    return ip_json


def get_ranges_for_service(ranges, service, subset):
    service_ranges = list()
    for prefix in ranges['prefixes']:
        if prefix['service'] == service and ((subset == prefix['region'] and subset == "GLOBAL") or (subset != 'GLOBAL' and prefix['region'] != 'GLOBAL')):
            print('Found ' + service + ' region: ' + prefix['region'] + ' range: ' + prefix['ip_prefix'])
            service_ranges.append(prefix['ip_prefix'])

    return service_ranges


def update_security_groups(new_ranges):
    client = boto3.client('ec2')

    global_security_groups = list()
    regional_security_groups = list()

    for sec_group_id in GLOBAL_SECURITY_GROUP_IDS:
        global_security_groups.append(
            get_security_groups_for_update(client, sec_group_id)
        )

    for sec_group_id in REGIONAL_SECURITY_GROUP_IDS:
        regional_security_groups.append(
            get_security_groups_for_update(client, sec_group_id)
        )

    print('Found ' + str(len(global_security_groups)) + ' Global HttpsSecurityGroups to update')
    print('Found ' + str(len(regional_security_groups)) + ' Regional HttpsSecurityGroups to update')

    result = list()
    global_https_updated = 0
    region_https_updated = 0

    for groups in global_security_groups:
        for group in groups:
            if update_security_group(client, group, new_ranges["GLOBAL"], INGRESS_PORTS['Https']):
                global_https_updated += 1
                result.append('Updated: ' + group['GroupId'])

    for groups in regional_security_groups:
        for group in groups:
            if update_security_group(client, group, new_ranges["REGION"], INGRESS_PORTS['Https']):
                region_https_updated += 1
                result.append('Updated: ' + group['GroupId'])

    result.append(
        'Updated: ' + str(global_https_updated) +
        ' of: ' + str(len(global_security_groups)) +
        ' CloudFront_g HttpsSecurityGroups'
    )
    result.append(
        'Updated: ' + str(region_https_updated) +
        ' of: ' + str(len(regional_security_groups)) +
        ' CloudFront_r HttpsSecurityGroups'
    )

    return result


def update_security_group(client, group, new_ranges, port):
    added = 0
    removed = 0

    if len(group['IpPermissions']) > 0:
        for permission in group['IpPermissions']:
            if permission['FromPort'] <= port and permission['ToPort'] >= port:
                old_prefixes = list()
                to_revoke = list()
                to_add = list()
                for range in permission['IpRanges']:
                    cidr = range['CidrIp']
                    old_prefixes.append(cidr)
                    if new_ranges.count(cidr) == 0:
                        to_revoke.append(range)
                        print(group['GroupId'] + ": Revoking " + cidr + ":" + str(permission['ToPort']))

                for range in new_ranges:
                    if old_prefixes.count(range) == 0:
                        to_add.append({ 'CidrIp': range })
                        print(group['GroupId'] + ": Adding " + range + ":" + str(permission['ToPort']))

                removed += revoke_permissions(client, group, permission, to_revoke)
                added += add_permissions(client, group, permission, to_add)
    else:
        to_add = list()
        for range in new_ranges:
            to_add.append({ 'CidrIp': range })
            print(group['GroupId'] + ": Adding " + range + ":" + str(port))
        permission = { 'ToPort': port, 'FromPort': port, 'IpProtocol': 'tcp'}
        added += add_permissions(client, group, permission, to_add)

    print(group['GroupId'] + ": Added " + str(added) + ", Revoked " + str(removed))

    return (added > 0 or removed > 0)


def revoke_permissions(client, group, permission, to_revoke):
    if len(to_revoke) > 0:
        revoke_params = {
            'ToPort': permission['ToPort'],
            'FromPort': permission['FromPort'],
            'IpRanges': to_revoke,
            'IpProtocol': permission['IpProtocol']
        }

        try:
            client.revoke_security_group_ingress(GroupId=group['GroupId'], IpPermissions=[revoke_params])
        except Exception as e:
            print(str(e))

    return len(to_revoke)


def add_permissions(client, group, permission, to_add):
    if len(to_add) > 0:
        add_params = {
            'ToPort': permission['ToPort'],
            'FromPort': permission['FromPort'],
            'IpRanges': to_add,
            'IpProtocol': permission['IpProtocol']
        }

        client.authorize_security_group_ingress(GroupId=group['GroupId'], IpPermissions=[add_params])

    return len(to_add)


def get_security_groups_for_update(client, security_group_id):
    response = client.describe_security_groups(GroupIds=[security_group_id])

    return response['SecurityGroups']


'''
Sample Event From SNS:
{
  "Records": [
    {
      "EventVersion": "1.0",
      "EventSubscriptionArn": "arn:aws:sns:EXAMPLE",
      "EventSource": "aws:sns",
      "Sns": {
        "SignatureVersion": "1",
        "Timestamp": "1970-01-01T00:00:00.000Z",
        "Signature": "EXAMPLE",
        "SigningCertUrl": "EXAMPLE",
        "MessageId": "95df01b4-ee98-5cb9-9903-4c221d41eb5e",
        "Message": "{\"create-time\": \"yyyy-mm-ddThh:mm:ss+00:00\", \"synctoken\": \"0123456789\", \"md5\": \"45be1ba64fe83acb7ef247bccbc45704\", \"url\": \"https://ip-ranges.amazonaws.com/ip-ranges.json\"}",
        "Type": "Notification",
        "UnsubscribeUrl": "EXAMPLE",
        "TopicArn": "arn:aws:sns:EXAMPLE",
        "Subject": "TestInvoke"
      }
    }
  ]
}
'''