In this chapter, we were focused on developing custom plugins for Elasticsearch. We learned how to properly set up your Maven project to be able to automatically build your Elasticsearch plugins. You saw how to develop a custom REST action plugin, and we extended Elasticsearch analysis capabilities by creating a plugin that included a custom token filter and new analyzer.

We've reached the end of the book, and we wanted to write a small summary and say a few words to the brave reader who managed to get to the end. We decided to write the second edition of Mastering Elasticsearch after writing Elasticsearch Server Second Edition. We thought that we had left a number of topics uncovered, and we wanted to write them in this book. We went from introducing Apache Lucene and Elasticsearch to querying and data handling—both on the Lucene index and the Elasticsearch level. We hope that, by now, you know how Lucene works and how Elasticsearch uses it, and you will find this knowledge worthy in your journey with this great search engine. We talked about some topics that can be useful when things are hot, such as I/O throttling, Hot Threads API, and how to speed up your queries. We also concentrated on things such as choosing the right query for the use case and Elasticsearch scaling.

Finally, we dedicated one chapter to discussing Java development on how to extend Elasticsearch with your own plugins. In the first version of the book, we also described the Java API briefly, but we decided it doesn't make sense. The API would require its own book and showing only some things regarding them just feels wrong. Hopefully, you'll be able to write your own plugins and even though we didn't write about all the possibilities, we hope that you'll be able to find the things we didn't write about.

Thank you for reading the book; we hope that you like it and that it brought you some knowledge that you were seeking, and that you'll be able to use it whether you use Elasticsearch professionally or just as a hobby.

Finally, please stop by at http://elasticsearchserverbook.com/ from time to time. In addition to the usual posts we make, we will publish the book fragments that didn't make it to the book or were cut down because the book would be too broad.