You can add a host to an HA cluster by calling one of the methods for moving hosts into a cluster. See Adding a Host to a Cluster. You might have to call HostSystem.ReconfigureHostForDAS_Task to reconfigure the host for HA if the automatic HA configuration fails.You can add a host to a cluster by calling the ClusterComputeResource.AddHost_Task method, which requires that you specify the host name, port, and password for the host to be added as a HostConnectSpec.