OPC UA Servers that are part of a RedundantServerSet have certain AddressSpace requirements. These requirements allow a Client to consistently access information from Servers in a RedundantServerSet and to make intelligent choices related to the health and availability of Servers in the RedundantServerSet.

Servers in the RedundantServerSet shall have an identical AddressSpace including:

The only Nodes that can differ between Servers in a RedundantServerSet are the Nodes that are in the local Server namespace like the Server diagnostic Nodes. A Client that fails over shall not be required to translate browse paths or otherwise resolve NodeIds. Servers are allowed to add and delete Nodes as long as all Servers in the RedundantServerSet will be updated with the same Node changes.

All Servers in a RedundantServerSet shall be synchronized with respect to time. This may mean installing a NTP service or a PTP service.

There are other important considerations for a redundant system regarding synchronization: