When you configure Enhanced Failover, you need to choose one node to be the primary node and the other to be the secondary. When iFIX starts, each SCADA node will start in standby mode, and then after SCADA-to-SCADA communication is established, choose its correct state. If both the primary and secondary nodes can communicate with each other, and they are both in the same state (either active or standby), then the primary will become active and the secondary will become standby.
During startup, if communication cannot be made to the partner node, then the node being started becomes the active node. If you can communicate with the partner node and it's active, nothing happens. However, if the partner node is also in standby node, the primary node becomes active.
If the secondary node starts more quickly than the primary, it will become the active SCADA node. When the primary starts in this case, it remains on standby until a failure causes it to switch.
When iFIX starts on the iClient, it attempts to establish iFIX networking communication with its primary and secondary SCADA Servers. If both nodes are available, the iClient establishes an iFIX networking connection with both of them but retrieves its data and alarms only from the active SCADA. If only one SCADA Server is available, the iClient establishes a connection with it. If neither SCADA Server is available, the iClient polls both nodes until it establishes a connection with at least one SCADA Server.
If an iClient loses its network connection to the active SCADA, the iClient fails over to the standby SCADA, if available. The client remains connected to the standby SCADA until the active SCADA becomes available to the client again. In this condition, the client displays an iFIX Notification message indicating that the client cannot receive alarms, cannot do writes, and may display data that is out of date. This message box closes within a minute after the iFIX networking connection to the active SCADA is restored. The message box will remain on the screen until the connection to the active node is restored, or until the SCADA nodes switch roles.
