A typical druid cluster consists of the following type of nodes -
- Master node
- Query Node
- Data Node
You can read more on here -
I am sorry, I do not understand, what do you mean by “how many clusters or sub-clusters are there in Apache Druid?”.
I don’t understand this question either - it’s like asking “how many MySQL instances can there be”. However many you install and configure.
Generally, one cluster is on multiple machines or pods, and you can install and configure as many as you like. If you mean, can multiple clusters share machines, you could use containers, or configure to use different ports or IP addresses, to keep them from stepping on each other, as long as you have sufficient cpu, RAM, bandwidth, disk space, etc.