bin/resque: add support for connecting with a cluster client

As `bin/resque` currently works, it pulls in the hostname to use from
the environment using `getenv`. The problem with this is that you cannot
pass in an array which is what the underlying Redis library uses[1] to
determine whether it initialises a `Credis_Client` or a `Credit_Cluster`
for the connection.

This solves that by introducing a new environment variable
(`REDIS_CLUSTER_ENABLED`) to determine when it should expand a comma
separated list of hosts to define as a cluster.

[1]: master/lib/Resque/Redis.php#L128

Author: jacobbednarz

bin/resque

@@ -37,14 +37,23 @@ if(empty($QUEUE)) {
  * Note: the 'user' part of the DSN URI is required but is not used.
  */
 $REDIS_BACKEND = getenv('REDIS_BACKEND');
+$REDIS_CLUSTER_ENABLED = getenv('REDIS_CLUSTER_ENABLED');
 
 // A redis database number
 $REDIS_BACKEND_DB = getenv('REDIS_BACKEND_DB');
-if(!empty($REDIS_BACKEND)) {
-    if (empty($REDIS_BACKEND_DB))
-        Resque::setBackend($REDIS_BACKEND);
-    else
-        Resque::setBackend($REDIS_BACKEND, $REDIS_BACKEND_DB);
+if (!empty($REDIS_BACKEND)) {
+	if (empty($REDIS_BACKEND_DB)) {
+		// Should we have clustering enabled, we accept a comma separated list of
+		// servers to pass to the backend. This tells the underlying client we should
+		// use the specific cluster client.
+		if (filter_var($REDIS_CLUSTER_ENABLED, FILTER_VALIDATE_BOOLEAN)) {
+			Resque::setBackend(explode(",", $REDIS_BACKEND));
+		} else {
+			Resque::setBackend($REDIS_BACKEND);
+		}
+	} else {
+		Resque::setBackend($REDIS_BACKEND, $REDIS_BACKEND_DB);
+	}
 }
 
 $logLevel = false;