Why do instances have different hostId on single compute node?

Issue

• There's only 1 compute node, and running multiple instances on it. All those instances belongs to admin or demo tenant.

• I think that hostId uniquely identifies a compute node for each instance which is running on, but it looks some of them have different hostId even when those are running on single compute node and I'm suspecting if something's going wrong..

• What is hostId?

• How's hostId calculated and associated to compute node?