What is ELK/EFK?

The ELK stack (now known as the Elastic Stack) is a collection of three open-source tools – Elasticsearch, Logstash, and Kibana. Elasticsearch is a NoSQL database used for search and analytics. Logstash is a data processing pipeline that ingests data from various sources, transforms it, and then sends it to a 'stash' like Elasticsearch. Kibana lets users visualize data with charts and graphs in Elasticsearch. It is used for log analytics, security information and event management (SIEM), and observability.