Introduction

When the SSDT installs a new version of the ODDEX application, it is normally done usually performed as a "rolling upgrade".   Rolling upgrades allow the application to be upgraded without shutting down the entire application.   The application is upgraded as users log off the previous version and are automatically connected to the new version on their next login.In layman terms, this means that the application is upgraded with minimal user disruption.    

However, occasionally, a small number of users will inconvenienced by being forcibly logged out, which requires the user to log back in unexpectedly.  If you care to know why this happens, please read the remainder of this page.

...

The SSDT executes ODDEX on more than one application server simultaneously. This provides load-balancing across the servers. On login, each user is randomly assigned to one of the available servers.  For the length of the user's session, the load-balancer ensures the user users will remain "connected" to the server where the their session resides.  

At the time of this writing up to three application servers are executing ODDEX at any given time.

...

At all times, at least one server is available for new sessions, giving the appearance that the system was never shut down.  As users log out of the previous version, they will be automatically connected to the new version.

Long Running Sessions

In practice, it often takes four to eight hours to complete a rolling upgrade.  This is because a few users keep an active session for the entire business day.  A single user can prevent the upgrade from proceeding by keeping a session active. For most upgrades, this is not an issue so the sessions are allowed to expire normally.  However, for an important upgrade or bug fix, the SSDT may decide to speed up the process by forcibly terminating a few users.   Whenever possible, we only terminate sessions that have been inactive for at least 15 minutes but occasionally are forced to terminate more active sessions. 

...