Third-Party Redundancy with Enterprise+
Third-party redundancy is used to ensure redundant access to a connected subsystem. The OPC Router primarily connects to a preferred target system and can switch to an alternative target system if necessary.
Typical use cases include plug-ins where a primary and an alternative server can be configured for the same target system, such as in a database connection.
When This Concept Is Relevant
This concept is relevant when it is not the OPC Router itself, but the connected third-party system that is to be configured for redundancy. The OPC Router remains a single instance but uses both a primary and an alternative remote system for the connection to a subsystem.
Prerequisites
The Enterprise+ add-on is required for this feature. This add-on is included in the Enterprise license. The corresponding feature name in the license overview is “Redundant Connection of Subsystems.” For more information on license assignment and other Enterprise+ features, see License Levels.
Features of the Enterprise+ Add-on in the Respective Plug-ins
Depending on the plug-in, the 3rd-party redundancy of the Enterprise+ add-on includes the following features in particular:
- OPC Client: Redundant connection to an OPC server in the OPC UA Plug-in and in the OPC Classic Plug-in
- MS SQL: Using an alternative SQL server via the failover settings
- SAP® Plug-in: Load balancing function for the SAP connection
Distinction from Other Redundancy Concepts
Difference from the OPC Router’s Secure Redundancy
Secure Redundancy makes the OPC Router itself redundant. To achieve this, a primary and a secondary service work together as a redundancy pair, with project synchronization as needed.
Third-party redundancy pursues a different goal: Here, the OPC Router itself remains unchanged, but a single connection to an external system can switch to an alternative remote system.
Difference from External HTTP(s) Failover
The HTTP(s) failover concepts concern the availability of the OPC Router’s server endpoints via reverse proxies or load balancers.
Third-party redundancy, on the other hand, does not concern the OPC Router’s server endpoints, but rather the connection of a third-party system behind a plug-in.
Typical Use Case
A typical use case is an OPC UA client connection with a primary and an alternate server. The OPC Router first attempts to use the primary OPC UA server. If this server is unreachable or if the configured life item no longer returns a valid state, the system can switch to the alternate server.
The actual high availability of the third-party system continues to be provided outside the OPC Router, for example through a redundant server configuration or a vendor-specific failover solution.
Where to Configure This Feature
The specific configuration is performed in the respective plug-in (see the section Functions of the Enterprise+ Add-on in the Respective Plug-ins).