Logstash (https://www.elastic.co/products/logstash) will take the logs, process them, and convert them into output. They can read any type of logs, such as system logs, error logs, and app logs. They are the heavy working component of this stack, which helps to store, query, and analyze the logs.
They act as a pipeline for event processing and are capable of processing huge amounts of data with the filters and, along with Elasticsearch, deliver results really fast. JHipster makes sure that the logs are in the correct format so that they can be grouped and visualized in the correct way.