With HA enabled, NN wo't start with "-upgrade". Since there has been a layout version change between 2.0.x and 2.1.x, starting NN in upgrade mode was necessary when deploying 2.1.x to an existing 2.0.x cluster. But the only way to get around this was to disable HA and upgrade.
The NN and the cluster cannot be flipped back to HA until the upgrade is finalized. If HA is disabled only on NN for layout upgrade and HA is turned back on without involving DNs, things will work, but finaliizeUpgrade won't work (the NN is in HA and it cannot be in upgrade mode) and DN's upgrade snapshots won't get removed.
We will need a different ways of doing layout upgrade and upgrade snapshot. I am marking this as a 2.1.1-beta blocker based on feedback from others. If there is a reasonable workaround that does not increase maintenance window greatly, we can lower its priority from blocker to critical.