OPC UA Redundancy

The OPC UA communication protocole offers standardized ways of achieving redundancy, as described in full detail here: OPC UA Online Reference - Server Redundancy

We support redundancy on both server and client side.

Server Redundancy

To configure redundancy on the server side we use Apis High Availability to set up a OpcUa "Redundant Server Set".

This will be a Non-transparent Redundancy Redundant Server Set.

By definition all servers shall have identical AddressSpace including:

  • identical NodeIds
  • identical browse paths and structure of the AddressSpace
  • identical logic for setting the the ServiceLevel. (defined by Apis HAGovernor)

OpcUa Namespace 2 (NS2) in Hive, reflect configuration and all variable/signals witch are connected. By default Hive-instances automaticly create an URI for NS2, based on computername and instancename. When configure a Redundant Server Set the NS2 uri have to be equal. This can be sett manually by changing the registry key NS2 under UAServer for all servers in the Redundant Server Set.

Apis support Cold and Hot server failover, see defenitions of Server Failover mode .

Connect to a Redundant Server Set

To create a connection to a Redundant Server Set use the Apis Connection Manager together with the Apis OpcUa. The ClusterItem in ApisCmxMgr define the connectionpoint, and shall be used as the Server property in the Apis OpcUa. The client will connect to the server with highest ServiceLevel. The ApisCnxMgr will continue to monitor the ServiceLevel of all servers in the set. If the ServiceLevel of the current used server indicate a degenerated server, the connection manager will switch to a server with the highest ServiceLevel, and the ApisOpcUa module will connect to the this server. Some data can be lost due to the time involved in reconnection to a new server.

This is defined as Warm failover. See Redundancy Failover mode .