MYSQLI DB Connection is not working in one class giving Warning: mysqli::__construct(): (HY000/2002):

Question

I am connecting to the amazon aws server. in one class my DBConnect class is working while in other, the same class is giving

Warning: mysqli::__construct(): (HY000/2002):No such file or directory 

The class code is below;

<?php
class DBConnect {

private $hostname;
private $username;
private $password;
private $dbname;

public function __construct ($conn_cred) {
    $this->hostname = $conn_cred['hostname'];
    $this->username = $conn_cred['username'];
    $this->password = $conn_cred['password'];
    $this->dbname   = $conn_cred['dbname'];
}

public static function connect($dbname) {
    // Include connection credentials
    $conn_cred = require_once 'constants/'.$dbname.'.credentials.php';
    // Set object
    $conn_obj = new self($conn_cred);
    // Establish Connection
    return $conn_obj->establish_connection();
}

private function establish_connection () {
    // Create connection    
    $conn = new mysqli($this->hostname, $this->username, $this->password, $this->dbname);
    // Check connection
    if ($conn->connect_error) {
        die("Connection failed: " . $conn->connect_error);
    } else {
    //    echo "Connected";
        return $conn;
    }
}
}

The class invoking line is

$dbObj = DBConnect::connect('cloudDBone');

cloudDBone.credentials.php

<?php
return array(
"driver"    => "mysql",
"hostname"  => "prodcloud.cshtaf5aoiog.ap-south-1.rds.amazonaws.com",
"username"  => "<-- myusername -->",
"password"  => "<-- mypwd -->",
"dbname"    => "<-- mydbname -->"
);

I am stuck in this. Any kind of help would be highly appreciated. Thanks