Understanding Clusters in OpenSearch

OpenSearch runs on Java Virtual Machines. Each JVM instance running OpenSearch can be considered as an OpenSearch node. To provide redundancy and scaling, OpenSearch supports the concept of a cluster. Multiple nodes running on one or more hosts (physical or virtual) can be grouped into a cluster, using a unique cluster name. Further, the index and source data managed by each node can be configured to suit load patterns and redundancy needs. Searches performed on a cluster will return integrated results from each of the nodes.

Different types of nodes can be present in a cluster. One node in the cluster is elected to be the master node, which is responsible for lightweight cluster-wide actions such as creating or deleting an index, tracking which nodes are part of the cluster, and deciding which shards to allocate to which nodes. Any master-eligible node (all nodes by default are master-eligible nodes) may be elected to become the master node by the master election process. OpenSearch transparently manages the process of gathering the response from node or nodes holding the data.

Note: In the PeopleSoft implementation of an OpenSearch cluster, the cluster contains only the master-data node, that is, the node can act both as a master and as a data node.

Depending on the purpose of your multi-node cluster, you may set up nodes on different machines or on a single machine. In a production environment, you would set up nodes on different machines when you want to achieve high availability. In a non-production environment, when you want to test the setup and multi-node cluster, you may set up multiple nodes on the same machine, but note that you may not be able to test the high-availability feature.

OpenSearch provides the ability to subdivide your index into multiple pieces called shards. When you create an index, you can simply define the number of shards that you want. Each shard is in itself a fully-functional and independent index that can be hosted on any node in the cluster. OpenSearch allows you to make one or more copies of your index’s shards into what are called replica shards, or replicas for short.

This topic discusses:

  • Setting up a cluster when you perform a fresh deployment of OpenSearch using the PeopleSoft delivered Deployment Packages (DPK).

  • Adding new nodes to an existing OpenSearch cluster.

  • Verifying the cluster setup.

  • Setting the number of replicas.

  • Starting and stopping a cluster.

  • Removing a node from a cluster.

  • Managing large indexes.