How to use reassign partition tool in Apache Kafka

This video explains about the usage of reassigning partition tool in Apache Kafka.

[masonlu]

my question is when the producer keep coming write logs to exsisting partion, meanwhile you are supose doing rebalance the partion, let's say you doing expending from 1 to 2, is this will be impact ? or we should stop producer wiring log first ? then doing rebalance partation ?

[vinG]

are you moving the partitions live ? meaning while there are producer writing on them?
im unable to find this information anywhere!
whenever i try this while producing data, i have error stating that the current broker is no more leader for partition X

[umas]

If there are 1000 topics whose partitions need to be moved, is there an easy way to build the topics-to-move.json file.

[cu]

I need info about how to create that json file. That's why I needed tutorial. I can run this command in shell just by google search. That shouldn't be point of tutorial.