elasticsearch is an open-source search technology that recently reached the stable 1.0 version after many years of development. It has a great API and works very well. Here’s a list of resources to help you learn about this product
Official resources
elasticsearch – the definitive guide
New book written by the elasticsearch team, will eventually be available as an ebook/paper copy but also available for free online. The work is in progress and you can submit issues on github since it’s open-source
http://www.elasticsearch.org/guide/en/elasticsearch/guide/current/index.html
official documentation
Where you can find the full documentation for the product
http://www.elasticsearch.org/guide/
Non-official resources
exploring elasticsearch
Free ebook with tutorials to learn more about elasticsearch when you get started. It was made before the 1.0 version so keep in mind it might not be entirely up to date, but it definitely serves as a good intro.
http://exploringelasticsearch.com/
Learn and play with Elasticsearch | Found
Lots of technical articles about elasticsearch, by a company that offers an elasticsearch as a service cloud solution. Very high quality
https://www.found.no/foundation/
Updated on December 8th 2014
Jérôme Gagnon-Voyer 