Also, in case it matters, the order of upgrades was:
HDP 2.1.15 and Ambari 1.7.0
HDP 2.1.15 and Ambari 2.0.1 (upgrade done 3 days ago)
HDP 2.2.6 and Ambari 2.0.1 (yesterday)
I checked our production cluster (HDP 2.1.15 / Ambari 2.0.1) and there is no “Versions” tab under “Stacks & Versions”, so it’s likely that was something that was added under the HDP2.2 upgrade.
Also – when upgrading, I used “UpgradeCatalog_2.1_to_2.2.4.json” to go to 2.2.6, because there was no related 2.2.6 upgrade catalog.
Finally … to the ambari developers … thank you! A few months ago I did a 2.1->2.2.0 upgrade, which was _much_ more painful at that time. The new upgradeHelper.py script is much nicer.