Learn about client-level failover

The AVEVA Adapter for RDBMS can be configured for failover by registering the adapter to a failover group managed by a failover endpoint.

Registering the adapter to a failover group allows multiple adapters to work in tandem to ensure constant data flow between the data source and the data destination. Failover groups minimize the likelihood of data loss if an adapter goes offline due to unexpected maintenance or a power outage.

Using client failover, you can:

• Register or unregister the adapter instance to a failover group.

• Perform runtime failover service parameter changes, such as failover mode and failover timeout.

• Query the current failover state, including the failover role, last data processed time, failover status, and adapter state.

Failover Role

The current failover Role is determined by the client failover endpoint. The current failover role is visible by querying the failover state, or by reviewing the failover status diagnostics streams. For additional information, see Failover status.

When an adapter with a valid client failover configuration registers with an endpoint and it is the only adapter registered in the group, it becomes the Primary adapter instance. If the adapter is not the only adapter registered in the client failover group, the Primary adapter instance will be the adapter with the highest FailoverScore value. The failover score value ranges from 0 to 100 and depends on the number of outstations that exist in the Good state.

Client-failover score

The adapter sends failover messages to the configured endpoint with the failover score, role, state, and processed time as part of OMF Health Data.

The failover score is determined by considering the status of individual adapter components and the total number of streams each component is set up to collect.

For example, for four components, each configured to handle 1000 streams:

• When all components are functioning correctly, the failover score is at its maximum, which is 100.

• If one of these components experiences a loss of connection to its data source, the failover score drops to 75.

• If two of the components experience a loss of connection to its data source, the failover score drops to 50.

In the worst-case scenario where all components lose their connections to their respective data sources, the failover score reaches its minimum value, which is 0.

Query current failover state

You can query the current failover state using the adapter's diagnostics. To query the current failover state, use any of the Configuration tools capable of making HTTP requests to run a GET command to the following endpoint:

http://<hostname>:<port>/api/v1/diagnostics/FailoverState

The following is an example of failover state returned from the adapter:

[

{

"role": "Primary",

"lastdataprocessedtime": "2025-01-01T00:00:00",

"failoverscore": "95",

"adapterstate": "Running"

}

]