Data domain cluster concepts

Leader node

The leader node of a data domain cluster is a single Dgraph process in the data domain cluster responsible for receiving and processing updates to the index and configuration. This node can also be configured to process queries, like other nodes. This node is responsible for generating information about the latest versions of the index, and propagating this information to the follower nodes.

When you create a new data domain cluster, the Endeca Server software creates and starts the leader node and then the follower nodes. Each data domain cluster (that is not read-only) is created with one leader node and a specified number of follower nodes.

The leader node periodically receives full or incremental index updates. It also receives administration or configuration updates. It is the only node in the data domain cluster that makes updates to the index.

After processing updates, the leader publishes a new version of the data and notifies all follower nodes, alerting them to start using the updated version of the index. The follower nodes acquire read-only access to an updated version of the index.

Follower node

A follower node is a node in the data domain cluster responsible for processing queries. The follower node does not update the index. When you create a data domain cluster (that is not read-only), the Endeca Server software creates and starts the required number of the follower nodes after starting the leader node for the data domain. (In the read-only data domain cluster, all nodes are allocated follower node roles by the Endeca Server).

During the process of acquiring access to the recently updated index, follower nodes continue to serve queries. Each query is processed against a specific version of the index available to it at any given time. Query processing performance may slow down as follower nodes acquire read-only access to the updated index.

Cluster Coordinator

The Cluster Coordinator provides coordination services between cluster nodes. For detailed information about the tasks it performs, see Role of the Cluster Coordinator.