Hello Gary,
When migrating license servers and dealing with client sessions that are bound to an old server, several important considerations and potential outcomes need to be addressed:
What Happens When the Old Server Goes Down
- Heartbeat Mechanism: Most license managers, including those used in academic settings, rely on a heartbeat mechanism to ensure that the client sessions are still connected to the license server. If the server goes down and the heartbeat is lost, clients typically have a grace period during which they will try to reconnect to the server.
- Rebinding to the New Server: Unfortunately, client sessions that are bound to the old server will not automatically rebind to the new server. The DNS CNAME change only affects new sessions. Existing sessions have cached the IP address of the old server and will not automatically update to the new server's IP.
- Session Behavior: Clients may continue to operate for a short grace period after losing connection to the license server. This period varies depending on the software and license manager configuration. After the grace period, if the client cannot reconnect to the license server, the session will typically terminate. This can result in loss of unsaved work.
- Work in Progress: If the session terminates abruptly, any unsaved work may be lost. Users should be advised to frequently save their work, especially during the transition period.
Strategies to Mitigate Issues
- User Communication: Clearly communicate with users about the migration and encourage them to save their work and restart their sessions to connect to the new server.
- Graceful Transition: If possible, configure the license manager to extend the grace period to allow users more time to transition. Keep the old server running as long as feasible to allow ongoing sessions to complete naturally.
- Testing and Validation: Before shutting down the old server, ensure thorough testing has been conducted to verify that the new server is handling all new sessions correctly.
- Backup and Recovery: Ensure that users are aware of backup and recovery options for their work, especially for long-running jobs.
I hope it helps!
