Couchbase Server can be used either in a standalone configuration, or in a cluster configuration where multiple Couchbase Servers are connected together to provide a single, distributed, data store.
In this description:
Couchbase Server or Node
A single instance of the Couchbase Server software running on a machine, whether a physical machine, virtual machine, EC2 instance or other environment.
All instances of Couchbase Server are identical, provide the same functionality, interfaces and systems, and consist of the same components.
Cluster
A cluster is a collection of one ore more instances of Couchbase Server that are configured as a logical cluster. All nodes within the cluster are identical and provide the same functionality and information. Information is shared across the entire cluster.
Clusters operate in a completely horizontal fashion. To increase the size of a cluster, you add another node. There are no parent/child relationships or hierarchical structures involved. This means that Couchbase Server scales linearly, both in terms of increasing the storage capacity and the performance and scalability.