This document discusses using the ELK stack (Elasticsearch, Logstash, Kibana) to centralize logging and visualize log data. It introduces the components of ELK - Logstash collects and processes logs, Elasticsearch stores the data, and Kibana visualizes it. The document demonstrates using Logstash to input Apache/Nginx logs and output to Elasticsearch, and using Kibana to view the data. It also compares traditional distributed logging to the benefits of centralizing logs with ELK.