Question: I am trying out pinot on top of docker. How do I create a set of unassigned instances so that I can add it as a server / broker later on under different tenants using the AddTenant command? Currently the StartServer / StartBroker command initiates a single instance under the default tenant. I can't seem to find the proper config to do this.

Yes, you can use AddTenant command to create tenants.

That is failing stating there are no unassigned server instances available. How can I add an unassigned server instance before this?

Here’s some docs on updating tags: https://docs.pinot.apache.org/operators/operating-pinot/rebalance/rebalance-brokers#updating-tags