'Create the SNS-based async topic.'

def create_async_sns_topic(self, lambda_name, lambda_arn):

    topic_name = get_topic_name(lambda_name)
    topic_arn = self.sns_client.create_topic(Name=topic_name)['TopicArn']
    self.sns_client.subscribe(TopicArn=topic_arn, Protocol='lambda', Endpoint=lambda_arn)
    self.create_event_permission(lambda_name=lambda_name, principal='sns.amazonaws.com', source_arn=topic_arn)
    add_event_source(event_source={'arn': topic_arn, 'events': ['sns:Publish']}, lambda_arn=lambda_arn, target_function='zappa.async.route_task', boto_session=self.boto_session)
    return topic_arn
