Hot standby nodes (HSNs) are spare, running nodes that improve availability and quickly recover performance levels in the event of a node failure. If one or more nodes fail, the system replaces the failed nodes with the same number of available HSNs.
When launching HSNs, the process automatically tags the new, spare nodes as hsn, distinguishing them from TPA nodes tagged as database. If a TPA node fails, NFR tags the failed node as FailedDatabase and an available HSN replaces it as the new, functional TPA node (database).
| TPA or HSN Tag | Description |
|---|---|
| instanceType : database | Functional TPA node |
| instanceType : FailedDatabase | Failed TPA node |
| instanceType : hsn | Running HSN |
| instanceType : TransitioningHSN | HSN used for configuration |
| instanceType : HSNWaiting | HSN deployed but not ready to use |
You can also delete HSNs and switch to traditional NFR, which provisions new TPA nodes to replace failed TPA nodes and takes more time.
If there are no HSNs or not enough available HSNs, NFR automatically spins up one or more replacement nodes, detaches the network-attached storage of the failed node, reattaches the network-attached storage to the new VM, migrates the secondary IPs from the failed node NIC to the new VM NIC, and reinstates the configuration. The replacement node is deployed from a snapshot of the active (control) node.