Logstash is an open-source, server-side data processing pipeline designed to ingest, transform, and route data to multiple outputs. The blog post by Alex Marquardt illustrates how to use Logstash to process data from various stock markets and direct it to distinct outputs. By using a CSV file with stock market benchmarks as input, the process involves converting CSV rows to JSON documents, creating document copies with the clone filter plugin, and filtering each document to retain only the relevant fields for specific stock markets like "SMI" and "FTSE". Metadata is added to guide the documents to their respective Elasticsearch outputs, which are indexed separately. This example demonstrates Logstash's capability to handle complex data processing tasks without relying on the beta pipeline-to-pipeline communication feature. The post also provides a detailed Logstash pipeline example that showcases the steps necessary for setting up and executing the described data processing workflow.