Scaling a cluster after a kubernetes upgrade

[BrendanThompson]

Is this a request for help?:

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Is this an ISSUE or FEATURE REQUEST? (choose one):

FEATURE REQUEST

What version of acs-engine?:

v0.19.1

Orchestrator and version (e.g. Kubernetes, DC/OS, Swarm)
Kubernetes v1.9.x -> v1.11.x

What happened:

When attempting to scale the cluster after performing an upgrade from v1.9.x to v.1.11.x I get the following error:

And the cluster won't scale properly. For all intents and purposes the agent pool scales, but it gets that error. Obviously not something useable unfortunately.

If however, I scale the cluster prior to an upgrade it works fine. Although it means that once an upgrade has occurred it cannot be scaled again.

What you expected to happen:
Expect to be able to scale a cluster after an upgrade has occurred.

How to reproduce it (as minimally and precisely as possible):

1. Create cluster with "orchestratorRelease": "1.9",
2. Upgrade cluster to 1.11.0-rc.3 using the acs-engine upgrade command
3. Scale cluster using acs-engine scale command

Anything else we need to know: