Zero Downtime Upgrade — limitations

Discussion created by Michael_Lowry on Sep 19, 2017
Latest reply on Sep 29, 2017 by Michael_Lowry
Recently we have used the Zero Downtime Upgrade* process to upgrade several of our systems from v11 to v12. During the course of testing, preparing, and performing these upgrades, we learned some things about ZDU that were not previously clear to us:
  • Regardingcompatibility mode:
    • Work processeswill not switchtodialog work processmode while the server is in compatibility mode.
    • When the AE is in compatibility mode, once an AE process running the old version stops, it cannot be restarted.
    • When all AE processes running the old version have stopped, this has the effect of finalizing the upgrade, making it impossible to perform therollbackfunction.
    • This means that if anything happens that causes all the old AE processes to stop — e.g., a system outage, power failure, or program fault — this will make it impossible to start these processes again or to perform a rollback.
  • Regarding therollbackfunction:
    • Rollback does not allow going completely back to the old version. It is intended only fortemporaryoperation using old-version AE processes.
    • Once the DB has been upgraded to the new version, it is not possible to downgrade the DB.
  • Regarding thefinalizestep:
    • The finalize step cannot be performed if certain types of tasks started on old-version AE processes are still active (present in the activities list). These includeC_PERIODtasks, but may also include other types. It may not be possible to completely remove these tasks from the relevant tables if no old-version AE processes are running. (PRB00138607 has been opened about this problem.)
    • This means that if all of the old-version AE processes have stopped, but there are still entries associated with old-version AE tasks in some DB tables, it may be impossible to finalize the upgrade without resorting to manual deletions from DB tables.
    • Because of this, in order to ensure a clean ZDU upgrade, it’s probably advisable to ensure that all tasks started on old-version AE processes have completed and have been deactivatedprior to stopping the last old-version AE process.
The ZDU documentation does not make all of these limitations clear. (The first two will be documented soon.)

Would someone from Automic please confirm whether this an accurate description of ZDU’s limitations?

* I noticed this morning that at least for ARA, Zero Downtime Upgrade was recently renamed to Minimal Downtime Upgrade. (Thanks to Carsten_Schmitz_7883 for pointing out that this documentation page pertains to ARA.)