I feel I need to know this, but I don't 
The Cloudwatch Logstash output doesn't exit when Logstash gets a kill signal (Ctrl+C), causing Logstash to eventually kill the process. If there's still metrics in the buffer when this happens, they won't get sent to AWS.
The input plugin has a stop method that you can override if anything special needs to be done to exit from the run method. It doesn't look like the output plugin has a similiar method? Or am I just missing something?
For reference: https://github.com/logstash-plugins/logstash-output-cloudwatch/issues/9