Using the Client Failover Service

You can configure the adapter for failover by registering the adapter to a failover group managed by the Client Failover Service.

For additional information on the Client Failover endpoint, review the Client Failover Service user guide.

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

The Client Failover Service allows for:

• Registering/unregistering the adapter instance to a failover group.

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

• Querying 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 looking at the failover status diagnostics streams. See Failover status for additional information.

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, if we had 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 with 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://<ClientFailoverEndpointHostname>:<ClientFailoverEndpointPort>/api/v1/diagnostics/FailoverState

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

{

"role": "Primary",

"lastdataprocessedtime": "2021-01-01T00:00:00",

"failoverscore": "95",

"adapterstate": "Running"

}