First of all, a big "thanks" to all of the Logstash and ELK Stack developers. Your product is certainly improving my job and a mind-blowing improvement over the tool that we are transitioning away from.
We get the logs that we parse (mostly Apache web server logs) on a monthly basis, so at the end of the month I can dump a month's worth of logs into the directories where the file inputs can snap them up. I have noticed that Logstash starts chewing through these logs at light speed, but after a couple days there is a noticeable slow-down in the rate at which these logs are parsed. Eventually, gaps will start to appear between when logs are parsed, and these gaps only lengthen with time. The worst that I have seen is almost 48 hours of no logs being indexed into Elasticsearch, after which a new log is suddenly processed. Sometimes, when the "flood-gates" re-open, it will be a huge number of Logstash events being processed, leaving me scratching my head wondering why Logstash didn't see them.
I am sure that there is something wrong with my Logstash config and would greatly appreciate any feedback to help alleviate this issue.
RAM: 128GB DDR3 1600MHz
CPU: 2 x 6-core Intel Xeon E5-2667 2.90GHz (hyper-threading enabled)
OS: CentOS 6.9
Logstash: v. 5.3.2
Many thanks for the assistance!