Elasticsearch 5.0 introduced the ingest node feature, which allows for pre-processing documents before indexing through an intercepting node that applies transformations defined in a pipeline. This blog post guides users on creating a custom ingest processor, specifically one that extracts URLs from a text field and stores them in an array, which can be used for various purposes like pre-fetching data or displaying URLs in applications. The process involves using tools like Gradle and Cookiecutter to set up and test the plugin, while highlighting the importance of unit testing and security considerations in Elasticsearch's Java environment. The blog also emphasizes the flexibility and potential of developing custom processors, encouraging users to explore possibilities such as geo-processing, language detection, and machine learning integration, all while maintaining performance by offloading tasks to dedicated nodes.