def do_db(self, arg):
        """
        Usage:
          db get_config
          db use_local_file [<filename>]
          db use_aws_instance [<instance_id>]
          db aws_list_regions
          db aws_get_region
          db aws_set_region [<region_name>]
          db aws_list_instances
          db aws_create_instance [<instance_id> <size> <username> <password>
                                  <dbname>]
          db aws_delete_instance [<instance_id>]
          db help
        """
        if arg['get_config']:
            self.db_get_config()
        elif arg['use_local_file']:
            self.db_use_local_file(arg, filename=arg['<filename>'])
        elif arg['use_aws_instance']:
            self.db_use_aws_instance(arg['<instance_id>'], arg)
        elif arg['aws_list_regions']:
            self.db_aws_list_regions()
        elif arg['aws_get_region']:
            self.db_aws_get_region()
        elif arg['aws_set_region']:
            self.db_aws_set_region(arg['<region_name>'])
        elif arg['aws_list_instances']:
            self.db_aws_list_instances()
        elif arg['aws_create_instance']:
            self.db_create_aws_db_instance(arg['<instance_id>'], arg['<size>'],
                                           arg['<username>'],
                                           arg['<password>'], arg['<dbname>'])
        elif arg['aws_delete_instance']:
            self.db_aws_delete_instance(arg['<instance_id>'])
        else:
            self.help_db()
Usage:
          db get_config
          db use_local_file [<filename>]
          db use_aws_instance [<instance_id>]
          db aws_list_regions
          db aws_get_region
          db aws_set_region [<region_name>]
          db aws_list_instances
          db aws_create_instance [<instance_id> <size> <username> <password>
                                  <dbname>]
          db aws_delete_instance [<instance_id>]
          db help