mysql -u xxx -p -h AWS_RDS_endpoint.com

<?php
  $servername = "aws_rds_endpoint.com";
  $username = "username";
  $password = "password";

  // Create connection
  $conn = new mysqli($servername, $username, $password);

  // Check connection
  if ($conn->connect_error) {
      die("Connection failed: " . $conn->connect_error);
  }
  echo "Connected successfully";
?>