How to shutdown/restart kafka cluster properly

Hi,

Sorry if this had been answered before. Although, I couldn't find any
information besides "controlled shutdown of broker", which, I believe
not fully applies here.

Could anyone suggest what would be the safest strategy to shut down
kafka cluster? Should brokers be brought down one-by-one or
simultaneously? Does this strategy change depend on whether
"controlled shutdown" is on?

According to my brief observation, ad-hoc broker shutdown (mix and
match INT, TERM and KILL signals to the most resilient brokers)
results in prolonged cluster start up, with a long chain of
"Recovering unflushed segment 0" seen on some brokers. Is it expected
to see these after each shutdown/restart?

Thanks in advance,