Measures reported by ESClusterTest

An Elasticsearch cluster is a group of one or more Elasticsearch nodes instances that are connected together. The Elasticsearch cluster efficiently distributes the tasks, searches and indexes across all the nodes. The nodes in the Elasticsearch cluster can be assigned different jobs or responsibilities:

• Data nodes - stores data and executes data-related operations such as search and aggregation
• Master nodes - in charge of cluster-ide management and configuration actions such as adding and removing nodes
• Client nodes - forwards cluster requests to the master node and data-related requests to data nodes
• Ingest nodes - for pre-processing documents before indexing

By default, each node is automatically assigned a unique identifier, or name, that is used for management purposes and becomes even more important in a multi-node, or clustered, environment. To add and efficiently manage a large amount of data in the cluster, Elasticsearch enables creating indices in the cluster. An index is a collection of documents with similar characteristics, and is identified by a name. Th index name is used to refer to the particular index while performing indexing, search, update, and delete operations against the documents in the cluster. The index can potentially store a large amount of data that can exceed the hardware limits of a single node. For example, a single index of a billion documents taking up 1TB of disk space may not fit on the disk of a single node or may be too slow to serve search requests from a single node alone. To solve this problem, Elasticsearch provides the ability to subdivide the index into multiple pieces called shards. When you create an index, you can simply define the number of shards you want. Each shard is a fully-functional and independent index that can be allocated to any node in the cluster. Furthermore, Elasticsearch allows you to create one or more copies of the shards called replica shards or replicas to provide high availability in case a primary shard/node goes offline or fails or becomes unavaiable for any reason. Using the shards, administrators can horizontally split/scale content volume and distribute and parallelize operations across the nodes. If the shards are not assigned to any nodes or in intializing/relocating state for longer time, the cluster may go imbalanced. To avoid this, administrator should continuously monitor the health of the cluster at shards level. This can be easily achieved using ESClusterTest!

This test continuously monitors the cluster, and the health of the cluster at regular intervals. In addition, this test also reports the count of active shards and the number of shards in the unassigned/initializing/relocating state. These revelations help administrators to track the balance of the cluster continously.

Output of the test: One set of results for the target Elasticsearch cluster.

The measures made by this test are as follows: