AWS Config カスタム LambdaルールでAmazon Elasticache for Redisの保管時暗号化設定をチェックしてみた

'''
Rule Name:
  redis-encrypted-at-rest-check-rule

Description:
  Check whether the Amazon ElastiCache Redis clusters have encryption at rest turned on. The rule is NON_COMPLIANT if the encryption at rest is not enabled.
Trigger:
  Periodic
Reports on:
  AWS::ElastiCache::CacheCluster
Rule Parameters:
  None
Scenarios:
  Scenario: 1
     Given: No Amazon ElastiCache Redis cluster in the AWS Account
      Then: Return "NOT_APPLICABLE"
  Scenario: 2
     Given: Encryption at rest not enabled for Amazon ElastiCache cluster
      Then: Return NON_COMPLIANT with Annotation "Encryption at rest not enabled for Amazon ElastiCache cluster: {Cluster_ID}"
  Scenario: 3
     Given: Encryption at rest enabled for Amazon ElastiCache cluster
      Then: Return COMPLAINT
'''
import json
import sys
import datetime
import boto3
import botocore

try:
    import liblogging
except ImportError:
    pass

##############
# Parameters #
##############

# Define the default resource to report to Config Rules
DEFAULT_RESOURCE_TYPE = 'AWS::ElastiCache::CacheCluster'

# Set to True to get the lambda to assume the Role attached on the Config Service (useful for cross-account).
ASSUME_ROLE_MODE = False

# Other parameters (no change needed)
CONFIG_ROLE_TIMEOUT_SECONDS = 900

#############
# Main Code #
#############

def get_replication_groups(ec_client):
    replication_groups = []
    marker = None
    replication_groups_result = {}
    while True:
        if not marker:
            replication_groups_result = ec_client.describe_replication_groups(MaxRecords=100)
        else:
            replication_groups_result = ec_client.describe_replication_groups(Marker=marker, MaxRecords=100)
        replication_groups.extend(replication_groups_result['ReplicationGroups'])
        if 'Marker' in replication_groups_result:
            marker = replication_groups_result['Marker']
        else:
            return replication_groups
def get_cache_clusters(ec_client):
    cache_clusters = []
    marker = None
    cache_clusters_result = {}
    while True:
        if not marker:
            cache_clusters_result = ec_client.describe_cache_clusters(MaxRecords=100, ShowCacheNodeInfo=False, ShowCacheClustersNotInReplicationGroups=True)
        else:
            cache_clusters_result = ec_client.describe_cache_clusters(Marker=marker, MaxRecords=100, ShowCacheNodeInfo=False, ShowCacheClustersNotInReplicationGroups=True)
        for cluster in cache_clusters_result['CacheClusters']:
            if cluster['Engine'] == 'redis':
                cache_clusters.append(cluster)
        if 'Marker' in cache_clusters_result:
            marker = cache_clusters_result['Marker']
        else:
            return cache_clusters

def generate_evaluations(eval_list, key,event):
    evaluations = []
    for cluster in eval_list:
        if cluster['AtRestEncryptionEnabled'] == False:
            evaluations.append(build_evaluation(cluster[key], 'NON_COMPLIANT', event, annotation="Encryption at rest not enabled for Amazon ElastiCache cluster: {}".format(cluster[key])))
        else:
            evaluations.append(build_evaluation(cluster[key], 'COMPLIANT', event))
    return evaluations

def evaluate_compliance(event, configuration_item):
    ec_client = get_client('elasticache', event)
    cache_clusters = get_cache_clusters(ec_client)
    evaluations = []
    replication_groups = get_replication_groups(ec_client)
    if not cache_clusters and not replication_groups:
        return build_evaluation(event['accountId'], "NOT_APPLICABLE", event)
    evaluations.extend(generate_evaluations(cache_clusters, 'CacheClusterId', event))
    evaluations.extend(generate_evaluations(replication_groups, 'ReplicationGroupId', event))
    return evaluations

####################
# Helper Functions #
####################

# This gets the client after assuming the Config service role
# either in the same AWS account or cross-account.
def get_client(service, event):
    """Return the service boto client. It should be used instead of directly calling the client.
    Keyword arguments:
    service -- the service name used for calling the boto.client()
    event -- the event variable given in the lambda handler
    """
    if not ASSUME_ROLE_MODE:
        return boto3.client(service)
    credentials = get_assume_role_credentials(event["executionRoleArn"])
    return boto3.client(service, aws_access_key_id=credentials['AccessKeyId'],
                        aws_secret_access_key=credentials['SecretAccessKey'],
                        aws_session_token=credentials['SessionToken']
                       )

# This generate an evaluation for config
def build_evaluation(resource_id, compliance_type, event, resource_type=DEFAULT_RESOURCE_TYPE, annotation=None):
    """Form an evaluation as a dictionary. Usually suited to report on scheduled rules.
    Keyword arguments:
    resource_id -- the unique id of the resource to report
    compliance_type -- either COMPLIANT, NON_COMPLIANT or NOT_APPLICABLE
    event -- the event variable given in the lambda handler
    resource_type -- the CloudFormation resource type (or AWS::::Account) to report on the rule (default DEFAULT_RESOURCE_TYPE)
    annotation -- an annotation to be added to the evaluation (default None)
    """
    eval_cc = {}
    if annotation:
        eval_cc['Annotation'] = annotation
    eval_cc['ComplianceResourceType'] = resource_type
    eval_cc['ComplianceResourceId'] = resource_id
    eval_cc['ComplianceType'] = compliance_type
    eval_cc['OrderingTimestamp'] = str(json.loads(event['invokingEvent'])['notificationCreationTime'])
    return eval_cc

def build_evaluation_from_config_item(configuration_item, compliance_type, annotation=None):
    """Form an evaluation as a dictionary. Usually suited to report on configuration change rules.
    Keyword arguments:
    configuration_item -- the configurationItem dictionary in the invokingEvent
    compliance_type -- either COMPLIANT, NON_COMPLIANT or NOT_APPLICABLE
    annotation -- an annotation to be added to the evaluation (default None)
    """
    eval_ci = {}
    if annotation:
        eval_ci['Annotation'] = annotation
    eval_ci['ComplianceResourceType'] = configuration_item['resourceType']
    eval_ci['ComplianceResourceId'] = configuration_item['resourceId']
    eval_ci['ComplianceType'] = compliance_type
    eval_ci['OrderingTimestamp'] = configuration_item['configurationItemCaptureTime']
    return eval_ci

####################
# Boilerplate Code #
####################

# Helper function used to validate input
def check_defined(reference, reference_name):
    if not reference:
        raise Exception('Error: ', reference_name, 'is not defined')
    return reference

# Check whether the message is OversizedConfigurationItemChangeNotification or not
def is_oversized_changed_notification(message_type):
    check_defined(message_type, 'messageType')
    return message_type == 'OversizedConfigurationItemChangeNotification'

# Check whether the message is a ScheduledNotification or not.
def is_scheduled_notification(message_type):
    check_defined(message_type, 'messageType')
    return message_type == 'ScheduledNotification'

# Get configurationItem using getResourceConfigHistory API
# in case of OversizedConfigurationItemChangeNotification
def get_configuration(resource_type, resource_id, configuration_capture_time):
    result = AWS_CONFIG_CLIENT.get_resource_config_history(
        resourceType=resource_type,
        resourceId=resource_id,
        laterTime=configuration_capture_time,
        limit=1)
    configuration_item = result['configurationItems'][0]
    return convert_api_configuration(configuration_item)

# Convert from the API model to the original invocation model
def convert_api_configuration(configuration_item):
    for k, v in configuration_item.items():
        if isinstance(v, datetime.datetime):
            configuration_item[k] = str(v)
    configuration_item['awsAccountId'] = configuration_item['accountId']
    configuration_item['ARN'] = configuration_item['arn']
    configuration_item['configurationStateMd5Hash'] = configuration_item['configurationItemMD5Hash']
    configuration_item['configurationItemVersion'] = configuration_item['version']
    configuration_item['configuration'] = json.loads(configuration_item['configuration'])
    if 'relationships' in configuration_item:
        for i in range(len(configuration_item['relationships'])):
            configuration_item['relationships'][i]['name'] = configuration_item['relationships'][i]['relationshipName']
    return configuration_item

# Based on the type of message get the configuration item
# either from configurationItem in the invoking event
# or using the getResourceConfigHistiry API in getConfiguration function.
def get_configuration_item(invoking_event):
    check_defined(invoking_event, 'invokingEvent')
    if is_oversized_changed_notification(invoking_event['messageType']):
        configuration_item_summary = check_defined(invoking_event['configuration_item_summary'], 'configurationItemSummary')
        return get_configuration(configuration_item_summary['resourceType'], configuration_item_summary['resourceId'], configuration_item_summary['configurationItemCaptureTime'])
    if is_scheduled_notification(invoking_event['messageType']):
        return None
    return check_defined(invoking_event['configurationItem'], 'configurationItem')

# Check whether the resource has been deleted. If it has, then the evaluation is unnecessary.
def is_applicable(configuration_item, event):
    try:
        check_defined(configuration_item, 'configurationItem')
        check_defined(event, 'event')
    except:
        return True
    status = configuration_item['configurationItemStatus']
    event_left_scope = event['eventLeftScope']
    if status == 'ResourceDeleted':
        print("Resource Deleted, setting Compliance Status to NOT_APPLICABLE.")
    return status in (['OK', 'ResourceDiscovered']) and not event_left_scope
    # return (status == 'OK' or status == 'ResourceDiscovered') and not event_left_scope

def get_assume_role_credentials(role_arn):
    sts_client = boto3.client('sts')
    try:
        assume_role_response = sts_client.assume_role(RoleArn=role_arn,
                                                      RoleSessionName="configLambdaExecution",
                                                      DurationSeconds=CONFIG_ROLE_TIMEOUT_SECONDS)
        if 'liblogging' in sys.modules:
            liblogging.logSession(role_arn, assume_role_response)
        return assume_role_response['Credentials']
    except botocore.exceptions.ClientError as ex:
        # Scrub error message for any internal account info leaks
        print(str(ex))
        if 'AccessDenied' in ex.response['Error']['Code']:
            ex.response['Error']['Message'] = "AWS Config does not have permission to assume the IAM role."
        else:
            ex.response['Error']['Message'] = "InternalError"
            ex.response['Error']['Code'] = "InternalError"
        raise ex

# This removes older evaluation (usually useful for periodic rule not reporting on AWS::::Account).
def clean_up_old_evaluations(latest_evaluations, event):

    cleaned_evaluations = []

    old_eval = AWS_CONFIG_CLIENT.get_compliance_details_by_config_rule(
        ConfigRuleName=event['configRuleName'],
        ComplianceTypes=['COMPLIANT', 'NON_COMPLIANT'],
        Limit=100)

    old_eval_list = []

    while True:
        for old_result in old_eval['EvaluationResults']:
            old_eval_list.append(old_result)
        if 'NextToken' in old_eval:
            next_token = old_eval['NextToken']
            old_eval = AWS_CONFIG_CLIENT.get_compliance_details_by_config_rule(
                ConfigRuleName=event['configRuleName'],
                ComplianceTypes=['COMPLIANT', 'NON_COMPLIANT'],
                Limit=100,
                NextToken=next_token)
        else:
            break

    for old_eval in old_eval_list:
        old_resource_id = old_eval['EvaluationResultIdentifier']['EvaluationResultQualifier']['ResourceId']
        newer_founded = False
        for latest_eval in latest_evaluations:
            if old_resource_id == latest_eval['ComplianceResourceId']:
                newer_founded = True
        if not newer_founded:
            cleaned_evaluations.append(build_evaluation(old_resource_id, "NOT_APPLICABLE", event))

    return cleaned_evaluations + latest_evaluations

def lambda_handler(event, context):
    if 'liblogging' in sys.modules:
        liblogging.logEvent(event)

    global AWS_CONFIG_CLIENT

    print(event)
    check_defined(event, 'event')
    invoking_event = json.loads(event['invokingEvent'])

    try:
        AWS_CONFIG_CLIENT = get_client('config', event)
        if invoking_event['messageType'] in ['ConfigurationItemChangeNotification', 'ScheduledNotification', 'OversizedConfigurationItemChangeNotification']:
            configuration_item = get_configuration_item(invoking_event)
            if is_applicable(configuration_item, event):
                compliance_result = evaluate_compliance(event, configuration_item)
            else:
                compliance_result = "NOT_APPLICABLE"
        else:
            return build_internal_error_response('Unexpected message type', str(invoking_event))
    except botocore.exceptions.ClientError as ex:
        if is_internal_error(ex):
            return build_internal_error_response("Unexpected error while completing API request", str(ex))
        return build_error_response("Customer error while making API request", str(ex), ex.response['Error']['Code'], ex.response['Error']['Message'])
    except ValueError as ex:
        return build_internal_error_response(str(ex), str(ex))

    evaluations = []
    latest_evaluations = []

    if not compliance_result:
        latest_evaluations.append(build_evaluation(event['accountId'], "NOT_APPLICABLE", event, resource_type='AWS::::Account'))
        evaluations = clean_up_old_evaluations(latest_evaluations, event)
    elif isinstance(compliance_result, str):
        if configuration_item:
            evaluations.append(build_evaluation_from_config_item(configuration_item, compliance_result))
        else:
            evaluations.append(build_evaluation(event['accountId'], compliance_result, event, resource_type=DEFAULT_RESOURCE_TYPE))
    elif isinstance(compliance_result, list):
        for evaluation in compliance_result:
            missing_fields = False
            for field in ('ComplianceResourceType', 'ComplianceResourceId', 'ComplianceType', 'OrderingTimestamp'):
                if field not in evaluation:
                    print("Missing " + field + " from custom evaluation.")
                    missing_fields = True

            if not missing_fields:
                latest_evaluations.append(evaluation)
        evaluations = clean_up_old_evaluations(latest_evaluations, event)
    elif isinstance(compliance_result, dict):
        missing_fields = False
        for field in ('ComplianceResourceType', 'ComplianceResourceId', 'ComplianceType', 'OrderingTimestamp'):
            if field not in compliance_result:
                print("Missing " + field + " from custom evaluation.")
                missing_fields = True
        if not missing_fields:
            evaluations.append(compliance_result)
    else:
        evaluations.append(build_evaluation_from_config_item(configuration_item, 'NOT_APPLICABLE'))

    # Put together the request that reports the evaluation status
    result_token = event['resultToken']
    test_mode = False
    if result_token == 'TESTMODE':
        # Used solely for RDK test to skip actual put_evaluation API call
        test_mode = True

    # Invoke the Config API to report the result of the evaluation
    evaluation_copy = []
    evaluation_copy = evaluations[:]
    while evaluation_copy:
        AWS_CONFIG_CLIENT.put_evaluations(Evaluations=evaluation_copy[:100], ResultToken=result_token, TestMode=test_mode)
        del evaluation_copy[:100]

    # Used solely for RDK test to be able to test Lambda function
    return evaluations

def is_internal_error(exception):
    return ((not isinstance(exception, botocore.exceptions.ClientError)) or exception.response['Error']['Code'].startswith('5')
            or 'InternalError' in exception.response['Error']['Code'] or 'ServiceError' in exception.response['Error']['Code'])

def build_internal_error_response(internal_error_message, internal_error_details=None):
    return build_error_response(internal_error_message, internal_error_details, 'InternalError', 'InternalError')

def build_error_response(internal_error_message, internal_error_details=None, customer_error_code=None, customer_error_message=None):
    error_response = {
        'internalErrorMessage': internal_error_message,
        'internalErrorDetails': internal_error_details,
        'customerErrorMessage': customer_error_message,
        'customerErrorCode': customer_error_code
    }
    print(error_response)
    return error_response