From the "ThingWorx 8 High Availability Administrator’s Guide":
ThingWorx HA requires the following:
ThingWorx 8.0 or higher
Two or more servers to operate ThingWorx in a HA environment
Apache ZooKeeper 3.4.5 or higher
Three servers to operate ZooKeeper in a HA environment
From the ThingWorx Connection Server Installation and Operations Guide:
The Connection Server handles all message routing to and from devices [by Thingworx.]
Navigate only makes requests to Windchill or other PLM applications, and so should have no need for the ThingWorx Connection Server.