Hello and thank you for the question.

The facets of the OPC UA specification define the basic principles of redundancy. However, the actual implementation needs to be defined by the applications taking into consideration application specific issues.

Similarly, the Prosys OPC UA Java SDK makes it possible to use the redundancy features but it doesn’t actually offer you any ready made implementation. For example, the SDK implements transfer subscriptions service which makes it possible to move subscriptions between sessions in the client and server applications. Another concurrency feature is the service level variable of servers (Objects -> Server -> ServiceLevel), which can be used to expose information about the operating condition of the server application. However, these are just constructs that you can use to build the concurrency, they are not a ready made implementation.

For example, the Client Redundancy Server Facet is defined in the OPC UA specification as “Support TransferSubscriptions Service to transfer a Subscription from one Session to another.” So, the SDK does support this.

And Redundant Client Facet is defined as “Clients … can failover to another Client (requires some out of band communication).” and optionally “The Client supports transferring Subscription from other Clients”.

For the Redundancy Transparent Server Facet and Redundancy Visible Server Facet, the technical details page (https://prosysopc.com/products/opc-ua-java-sdk/technical-details/) does mention that “Requires application implementation”. In these cases, the handling of redundancy is really an application specific matter.

I would suggest that you start by looking at the general explanation about redundancy in OPC UA specification. The specification part 4, page 94 onwards handles this topic (version 1.03 specification). You can access the specification part 4 at https://opcfoundation.org/developer-tools/specifications-unified-architecture/part-4-services/ (this requires a free account to be created at the OPC Foundation website).