Failover support
- Last UpdatedJun 26, 2025
- 1 minute read
- PI System
- Adapter for OPC UA 1.6
- Adapters
The OPC UA adapter supports Alarms and Conditions in both Client-side and Server-side Failover scenarios.
Client-side failover
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In Hot failover mode, the secondary adapter instance has a failover buffer for data, which works for events since events flow to the same buffer.
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In Warm failover mode, the secondary adapter instance can subscribe to alarms and conditions only after failover. Events are processed after the secondary adapter becomes the primary adapter. Some real time events will be lost, but Condition Refresh ensures the Alarms and Conditions that are in the retained state are processed.
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In Cold failover mode, the secondary adapter becomes primary and creates a connection and an event subscription. Some real time events will be lost, but Condition Refresh ensures the Alarms and Conditions that are in the retained state are processed.
Server-side failover
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If the servers are set to Cold or Warm failover, the adapter creates a subscription to events and performs a Condition Refresh. This ensures the Alarms and Conditions that are in the retained state are processed.
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If the server is set to Hot failover, the adapter performs a Condition Refresh if a RefreshRequiredEventType event notification is received from the Server.