This chapter gave you an overview of Elasticsearch and why it's important to proactively monitor a cluster. To summarize the points from the chapter:
Elasticsearch is an open source scalable, fast, and fault-tolerant search engine
Elasticsearch is built on top of Apache Lucene, the same library that powers Apache Solr
Monitoring tools will help us get a better understanding of our cluster and will let us know when problems arise
As helpful as monitoring tools are, it's up to us to actually diagnose and fix cluster issues
In the next chapter, we'll cover how to get a simple Elasticsearch cluster running and loaded with data, and how to install several monitoring tools.