Connect to remote MySQL server with SSL from PHP

"Unfortunately I can't use mysqli lib because have too many working adapters for pdo_mysql."

You're using the old MySQL extension ("mysql_connect"), which is no longer under development (maintenance only). Since you're using PHP 5, you may want to use MySQLi, the MySQL Improved Extension. Among other things, it has an object-oriented interface, support for prepared/multiple statements and has enhanced debugging capabilities. You can read more about converting to MySQLi here; more about the mysqli class itself here.

Here is some sample code that may help you get started:

<?php
ini_set ('error_reporting', E_ALL);
ini_set ('display_errors', '1');
error_reporting (E_ALL|E_STRICT);

$db = mysqli_init();
mysqli_options ($db, MYSQLI_OPT_SSL_VERIFY_SERVER_CERT, true);

$db->ssl_set('/etc/mysql/ssl/client-key.pem', '/etc/mysql/ssl/client-cert.pem', '/etc/mysql/ssl/ca-cert.pem', NULL, NULL);
$link = mysqli_real_connect ($db, 'ip', 'user', 'pass', 'db', 3306, NULL, MYSQLI_CLIENT_SSL);
if (!$link)
{
    die ('Connect error (' . mysqli_connect_errno() . '): ' . mysqli_connect_error() . "\n");
} else {
    $res = $db->query('SHOW TABLES;');
    print_r ($res);
    $db->close();
}
?>

If PDO_MYSQL is really what you want, then you need to do something like this:

<?php
$pdo = new PDO('mysql:host=ip;dbname=db', 'user', 'pass', array(
    PDO::MYSQL_ATTR_SSL_KEY    =>'/etc/mysql/ssl/client-key.pem',
    PDO::MYSQL_ATTR_SSL_CERT=>'/etc/mysql/ssl/client-cert.pem',
    PDO::MYSQL_ATTR_SSL_CA    =>'/etc/mysql/ssl/ca-cert.pem'
    )
);
$statement = $pdo->query("SHOW TABLES;");
$row = $statement->fetch(PDO::FETCH_ASSOC);
echo htmlentities($row['_message']);
?>

However, only recent versions of PHP have SSL support for PDO, and SSL options are silently ignored in (at least) version 5.3.8: see the bug report.

Good luck!

if your using PHP 7.3 and AWS PEM file , Use below code to connect DB with ssl

UR AWS PEM FILE PATH =/home/cert/rds2019.pem
$mysqli = mysqli_init();
$mysqli->ssl_set(NULL,NULL,'UR AWS PEM FILE PATH',NULL,'DHE-RSA-AES256-SHA');
$mysqli->options(MYSQLI_OPT_SSL_VERIFY_SERVER_CERT, true);
$mysqli->real_connect($dbHostName, $dbUserName, $dbPassword, $dataBaseName,PORT,NULL, MYSQLI_CLIENT_SSL);

return $mysqli;

For PDO Connection

$pdo = new PDO('mysql:host='.$dbHostName.';dbname='.$dataBaseName.'', $dbUserName, $dbPassword, array(
            //PDO::MYSQL_ATTR_SSL_KEY    =>NULL,

            //PDO::MYSQL_ATTR_SSL_CERT=>NULL,

            PDO::MYSQL_ATTR_SSL_CA    =>'UR AWS PEM FILE PATH',
            PDO::MYSQL_ATTR_SSL_CAPATH    =>NULL,
            PDO::MYSQL_ATTR_SSL_CIPHER    =>'DHE-RSA-AES256-SHA',
            PDO::MYSQL_ATTR_SSL_VERIFY_SERVER_CERT => false
            )
        );
return $pdo;