Will old sessions still bound to the old license server migrate to new license server upon loss of heartbeat?

We recently migrated our academic & classroom concurrent licenses from one server to another:

• all clients use 2 line SERVER cname ANY port / USE_SERVER license file so they never have to adjust anything
• server license files use real host name or own alias
• install license software on new server with new host name or alias
• deactivate licenses on old (license service remains up)
• activate license on new, download new codes, start new license service
• test new with a client configured to underlying host name or alias
• adjust DNS cname to new server
• all new sessions use new server
• all previously started sessions remain "bound" to the old server as it must cache the IP or such
• these gradually wither away as old sessions are ended
• request remaining old session users save & restart

Eventually though it is time to turn off the old server, or it may crash, or the old MLM license service may accidentally terminate. The old service cannot be restarted as it is no longer activated, ie it has been living on borrowed time.

What happens to any remaining "old" sessions once they detect loss of heartbeat? Will the IP or whatever be uncached on the client so it can "rebind" to the current SERVER cname and seamlessly carry on? Is there a way to force this? Or will the session be permanently "zombied"? Will any work still in progress be saved? Some users run jobs that take weeks to complete.

Answer 1

[Prateekshya]

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

1. 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.
2. 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.
3. 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.
4. 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

1. 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.
2. 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.
3. 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.
4. 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!