elastic/logstash

Logstash is one of the four pieces in the Elastic Stack, sitting next to Beats, Elasticsearch, and Kibana. The README describes it as a server-side data processing pipeline. In plain terms, it takes data such as log files, events, or other streams from many sources at once, transforms or filters the data along the way, and then sends the result somewhere else for storage or analysis. The Elastic company built it to feed their search engine Elasticsearch, but the destination can be anything you like. The project is extensible by design. The README mentions that there are over 200 plugins already written, and that writing your own is easy. Plugins live in separate repositories under the logstash-plugins GitHub organisation, and each one is packaged as a self-contained Ruby gem published to RubyGems.org. Bug reports and pull requests for a specific plugin are meant to go to that plugin's own repo, while this main repository handles the core engine. Most of the README is aimed at people who want to build Logstash from source rather than just use it. The prerequisites are JDK 21, JRuby 10.0.5.0, and the Ruby tools rake and bundler. There are notes for using the RVM Ruby version manager, and instructions for setting environment variables that control whether you build the full version or only the open-source-licensed parts. The build itself runs through Gradle. The README shows the commands to install development dependencies, install default plugins, and then start Logstash with a tiny pipeline that reads from your keyboard and prints back to the screen. There is also a tip about a tool called Drip, which keeps the Java virtual machine warm between commands so that repeated test runs start faster. The rest of the file covers testing and building release artifacts. Core tests use RSpec for the Ruby code and JUnit for the Java code, and Gradle tasks are provided for unit tests, Java-only tests, integration tests, and single specs. For shipping, Gradle tasks build tarball or zip distributions in a local build directory.