Elasticsearch tries very hard to make the complex simple, and to a large degree it succeeds in this. That said, search and distributed systems are complex, and sooner or later you have to get to grips with some of the complexity in order to take full advantage of Elasticsearch.
Complexity, however, is not the same as magic. We tend to view complex systems as magical black boxes that respond to incantations, but there are usually simple processes at work within. Understanding these processes helps to dispel the magic—instead of hoping that the black box will do what you want, understanding gives you certainty and clarity.
This is a definitive guide: we help you not only to get started with Elasticsearch, but also to tackle the deeper, more interesting topics. These include Life Inside a Cluster, Distributed Document Store, Distributed Search Execution, and Inside a Shard, which are not essential reading but do give you a solid understanding of the internals.
The first part of the book should be read in order as each chapter builds on the previous one (although you can skim over the chapters just mentioned). Later chapters such as Proximity Matching and Partial Matching are more standalone and can be referred to as needed.