do apps with producers have to be restarted if cluster goes down and comes back up?

Hi,

A few questions on timing related issues when certain parts of kafka go
down.

1. If zookeeper goes down, then I bring it back online, do I have to
restart the brokers?
2. If the brokers go down, producers will be erroring out. When the
brokers are back online, do I have to restart the processes with producers?

3. When servers are restarted, how can you gaurantee that first the
zookeeper server come online, THEN the brokers, and THEN the webapp's with
the producers? Or is the timing not that strict because of e.g. timeout
re-connect durations?

Thanks.