The failover Kepware OPC-UA server works the same as the OPC-UA server with the exception that you need to have two copies of Kepware setup, preferably on different servers. The failover Kepware OPC-UA server will be used in the event the primary Kepware server goes down. To enable failover, check the box to Show advanced properties in the New OPCUA Connection Settings, set the Failover Enabled property to 'true,' and specify the Failover Endpoint.
The Backup properties should be used when a pair of redundant Ignition Gateways are trying to look at the same Kepware OPC-UA server. Both the Backup Discovery URL and Backup Endpoint URL properties need to be configured.
For additional information on Failover, refer to OPC-UA Connections and Settings.
When connecting to KepServer, some versions may not allow anonymous connections by default. This typically means you need to specify user credentials for Ignition to use in the OPC-UA server connection. Alternatively, individual Kepware Projects can allow anonymous login. For more information, take a look at KepServer's documentation.
While the above example is specific to KEPServerEX, the same concepts apply to connecting to any other third party OPC server that accepts OPC-UA client connections. The only difference may be in the way that the certificates are accepted on the server.
The Ignition OPC-UA server sends the client certificate to the third party OPC server when it tries to make the connection, however if the OPC server is not designed to expect these certificates then there may not be a straight forward way to accept them. In these cases you can manual download a client ticket from Ignition and supply it to the OPC server in the appropriate manner.