Laravel 5 using 2 db connections join 2 tables

How can I join 2 tables which are located on 2 different servers.

I setup db configs:

'mysql' => [
            'driver' => 'mysql',
            'host' => env('DB_HOST', '127.0.0.1'),
            'port' => env('DB_PORT', '3306'),
            'database' => env('DB_DATABASE', 'forge'),
            'username' => env('DB_USERNAME', 'forge'),
            'password' => env('DB_PASSWORD', ''),
            'unix_socket' => env('DB_SOCKET', ''),
            'charset' => 'utf8mb4',
            'collation' => 'utf8mb4_unicode_ci',
            'prefix' => '',
            'strict' => false,
            'engine' => null,
            'options'   => [
                \PDO::ATTR_EMULATE_PREPARES => true
            ]
        ],

        'mysql2' => [
            'driver' => 'mysql',
            'host' => '132.133.22.9',
            'port' => '3306',
            'database' => 'contracts',
            'username' => 'asdsdsa',
            'password' => 'asdsad',
            'unix_socket' => env('DB_SOCKET', ''),
            'charset' => 'utf8mb4',
            'collation' => 'utf8mb4_unicode_ci',
            'prefix' => '',
            'strict' => false,
            'engine' => null,
            'options'   => [
                \PDO::ATTR_EMULATE_PREPARES => true
            ]
        ],

I'm able to access only one like DB::connection('mysql')->table('elements')->get();

How can I use leftJoin for two tables on two different servers?

lets say I have:

elements (server1): id, class_id

classes (server2) id, name

via Chebli Mohamed