How to connect MariaDB in S3(Amazon) server.

Hi,

I'm using amazon s3 server and marianDB, the DB is not connect show the below error.

A PHP Error was encountered
Severity: Warning
Message: mysqli::real_connect(): (HY000/2002): No such file or directory
Filename: mysqli/mysqli_driver.php
Line Number: 201
Backtrace:
File: /var/www/html/summitapp/core/application/controllers/Client.php
Line: 9
Function: model
File: /var/www/html/summitapp/core/index.php
Line: 315
Function: require_once

-----------------------------------------

A Database Error Occurred
Unable to connect to your database server using the provided settings.
Filename: core/CodeIgniter.php
Line Number: 518


And my Database configuration

$db['default'] = array(
    'dsn'    => '',
    'hostname' => 'localhost',
    'username' => 'root',
    'password' => 'Root@2018',
    'database' => 'example',
    'dbdriver' => 'mysqli',
    'dbprefix' => '',
    'pconnect' => FALSE,
    'db_debug' => (ENVIRONMENT !== 'production'),
    'cache_on' => FALSE,
    'cachedir' => '',
    'char_set' => 'utf8',
    'dbcollat' => 'utf8_general_ci',
    'swap_pre' => '',
    'encrypt' => FALSE,
    'compress' => FALSE,
    'stricton' => FALSE,
    'failover' => array(),
    'save_queries' => TRUE
);

OS                         : Amazon Linux AMI
PHP version           : 7.0.29
Codeigniter version : 3.1.8
MariaDB   version   : 10.3.1

Please tell me how to connect DB