After creating a reference to the server instance or cluster, enable the server instance or cluster using enable-http-lb-server. If you used a server instance or cluster as the target when you created the load balancer configuration, you must enable it. To do this using the Admin Console, on the left frame, click the HTTP Load Balancers node and then click the desired load balancer listed under the node. Now, open the Targets tab and in the Targets table, click the check box next to the instance you want to enable and click Enable.
For more information, see the documentation for enable-http-lb-server .