5.14.3 Redundant A & C servers

In an OPC UA Server that is implementing the A & C Information Model and that is configured to be a redundant OPC UA Server the following behaviour is expected:

• The EventId is used to uniquely identify an Event. For an Event that is in each of the redundant Servers, it shall be identical. This applies to all standard Events, Alarms and Conditions. This may be accomplished by sharing of information between redundant Server (such as actual Events) or it may be accomplished by providing a strict EventId generating algorithm that will generate an identical EventId for each Event

• It is expected that for cold or warm failovers of redundant Servers, Subscription for Events shall require a Refresh operation. The Client shall initiate this Refresh operation.

• It is expected that for hot failovers of redundant Servers, Subscriptions for Events may require a Refresh operation. The Server shall issue a RefreshRequiredEventType Event if it is required.

• For transparent redundancy, a Server shall not require any action be performed by a Client.