When the OPC Client plugin role is connected to two OPC servers, you can configure the plugin to operate in failover mode or in redundancy mode.
- For failover to work properly, both OPC servers must have the same node IDs.
- If you change this operation mode, you must deactivate, and then reactivate, the plugin role for the change take effect.
Failover mode is the default operation mode for the plugin when two connections are configured. In this mode, the OPC Client plugin connects to both configured OPC servers, but only listens for data change on the active server. On the Connection page of the plugin, the active server is indicated by a green icon ().
The active server is usually the first server with which the OPC Client plugin establishes a connection. The order in which the servers are listed does not affect which server is the active server.
When the connection between the plugin and the active server is lost, the connection will fail over to the next active server.
- If Server 1 goes offline, Server 2 becomes the active server, and the plugin will start listening for data changes on Server 2.
- If Server 1 comes back online, Server 2 will remain the active server, as long as it is connected.
Redundancy mode is enabled by selecting Redundancy mode at the bottom of the Servers list. In this operation mode, the OPC Client plugin connects to both configured OPC servers, and listens for data change on both servers.
State changes of OPC tags are processed by the rule engine of the plugin. If both OPC servers are properly configured with the same node IDs, alarms and events used in rules are only triggered once because the plugin receives two data changes with identical values.