Per https://www.elastic.co/blog/licensing-change Elasticsearch (which stores data collected by Logstash) and Kibana (which displays log data) will be switching to the Server Side Public License which according to Wikipedia is not OSI approved nor Debian Free Software Guidelines compatible.
Starting with the upcoming Elastic 7.11 release, we will be moving the Apache 2.0-licensed code of Elasticsearch and Kibana to be dual licensed under SSPL and the Elastic License, giving users the choice of which license to apply.
see also T272111: Elasticsearch, a CirrusSearch dependency, is switching to SSPL/Custom licence for use of Elasticsearch in MediaWiki extensions