Question 1
For curiosity, just want to know is Ray head node actually running multiple driver processes or only one driver process?
Based on this diagram, it seems it runs multiple driver processes.
It would be great to introduce how they are actually being used. Thanks! 
You can attach multiple driver processes to the same ray head node.
Thanks @Chen_Shen ! I have two more follow up questions.
Question 2
Based on Key Concepts — Ray 2.8.0
Ray driver processes which run Ray jobs
In this case, what is the difference between driver processes and worker processes?
Question 3
As Ray driver processes run Ray jobs. If one job submit to Ray cluster (Head), when having multiple driver processes, who helps decide which Ray driver process pick the job? Any algorithm? Thanks!
In this case, what is the difference between driver processes and worker processes?
A driver is a special worker process that executes the top-level application (e.g., __main__ in Python).
As Ray driver processes run Ray jobs. If one job submit to Ray cluster (Head), when having multiple driver processes, who helps decide which Ray driver process pick the job? Any algorithm? Thanks!
Similar to you can run multiple processes in a operating system, you can also run multiple independent jobs, each of which runs in their own drivers.
you can find a detailed explanation of driver versus worker in ray white paper.
Thank you so much!
The Ray v2 Architecture white paper is very helpful to help understand!