A system that operates using Open Platform Communications (OPC) Unified Architecture (UA) includes: a redundant server set including a first OPC UA server and a second OPC UA server; an OPC UA client that designates an endpoint Uniform Resource Locator (URL) to communicate with the redundant server set; and a load balancer (LB) connected between the redundant server set and the OPC UA client. The OPC UA client sends a request for connection to the endpoint URL. The first OPC UA server is an active server. The second OPC UA server is a standby server. The LB proxies the connection to the first OPC UA server. The end point ULR is different from a URL of each of the first OPC UA server and the second OPC UA server.