How to handle if logstash restart/reinstall or i do have multi logstash ?

[gogovan-vincentngai]

What i would like to know if i reinstall logstash / i need upgrade logstash verison
how it will know which log i already send to ELK

or
if i have more then one logstash on server (such as if i have ELB and two logstash behind it for HA feature)