Bad gateway

I have a simple MySQL setup master-slave with one WordPress site.
– MySQL services are on two different servers (Windows Server 2008)
– WordPress is on a Windows Server 2008 too and can access both MySQL instances

Problems:

1. When i activate HyperDB then the whole WordPress site is slow…
And sometimes i get a 502 – Bad gateway response on wp-admin section

2. When i stop the MySQL master service then WordPress respond with a Bad Gateway response (502)

I can see WordPress 10 connections on my slave in this situation…

This is my config for HyperBD:
$wpdb->add_database(array(
‘host’ => DB_HOST, // If port is other than 3306, use host:port.
‘user’ => DB_USER,
‘password’ => DB_PASSWORD,
‘name’ => DB_NAME,
));

$wpdb->add_database(array(
‘host’ => ‘x.x.x.x:2470’, // If port is other than 3306, use host:port.
‘user’ => DB_USER,
‘password’ => DB_PASSWORD,
‘name’ => DB_NAME,
‘write’ => 0,
‘read’ => 1,
‘dataset’ => ‘global’,
‘timeout’ => 0.2,
));

https://www.ads-software.com/extend/plugins/hyperdb/