Example for connecting Lithium apps to a MongoDB replica set

connections.php

/**
 * Example of a production database called "db_prod" connecting to a replica set 
 * running on two systems, "db1" and "db2" with the replica set name of "prod_01".
 *
 * This setup assumes that you're running a recent version of MongoDB as well as
 * the PHP extension.
**/
Connections::add('default', array(
	'production' => array(
		'type' => 'MongoDb',
		'database' => 'db_prod',
		'host' => array(
			'db1.mywebsite.com',
			'db2.mywebsite.com'
		),
		'replicaSet' => 'prod_01',
		'setSlaveOkay' => true
	)
)

The important part about this is the setSlaveOkay part, as you won't be able to do much but throw errors without it.