The Elasticsearch RESTful API provides a powerful toolset for collecting performance metrics about your clusters, nodes, and indices. The Node Stats API offers detailed information about nearly every metric from the previous Part 1, except for overall cluster health and pending tasks. This section covers how to query various APIs, including Cluster Health, Pending Tasks, cat API, dedicated monitoring tools such as ElasticsearchHQ, Kopf, and Marvel, which provide valuable insights into your cluster's performance and help you identify potential issues. These tools can be used individually or in combination to create a comprehensive monitoring solution for your Elasticsearch cluster.