Sometimes, I need to reconfigure Logstash config.

Without restart the services, just send a SIGHUP to the running Logstash process.

$ pgrep -U logstash
$ kill -SIGHUP 17913

You can see on Logstash log, it just already reloads.

$ tail -f /var/log/logstash/logstash-plain.log
[2021-05-09T16:35:12,815][WARN ][logstash.runner          ] SIGHUP received.
[2021-05-09T16:35:14,184][INFO ][logstash.pipelineaction.reload] Reloading pipeline {""=>:main}
[2021-05-09T16:35:17,143][INFO ][logstash.javapipeline    ][main] Pipeline terminated {""=>"main"}

My new Logstash config has been successfuly reloaded and ready to process a bunch of log again.