Add this block inside the top-level array returned by config/config.php:

'production_factory' => array(
    'enabled' => true,
    'api_url' => 'http://127.0.0.1:8787',
    'api_token' => '<THIS_YOU_PRODUCTION_API_TOKEN>',
    'connect_timeout_seconds' => 5,
    'request_timeout_seconds' => 30,
    'poll_interval_seconds' => 5
),

Development tunnel example (run in a separate terminal and keep it open):

ssh -N -L 8787:127.0.0.1:8000 root@YOUR_FACTORY_SERVER

Alternative environment variables supported by V2.1:
THIS_YOU_PRODUCTION_API_ENABLED=1
THIS_YOU_PRODUCTION_API_URL=http://127.0.0.1:8787
THIS_YOU_PRODUCTION_API_TOKEN=...

Never commit the API token to source control.