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Quick Definition
A cluster is a group of connected machines (nodes) that work together as a single system to run workloads. In Kubernetes, a cluster pools compute resources across nodes and schedules containers onto them, forming the unit on which costs are incurred and allocated.
A cluster is a set of servers that act as a single unit. Instead of running an application on one machine that can fail, you run it across a cluster that shares the load and survives individual failures.
In the Kubernetes world, the cluster is the universe: nodes provide the capacity, pods run the workloads, and the control plane schedules everything. For cost purposes, clusters create a puzzle: the cloud bills you per node, but many teams share those nodes, so understanding who spends what requires Kubernetes cost allocation.
Example. Eight teams share one 40-node cluster. The cloud bill says $48K a month and nothing else. Cost allocation reveals one team's over-provisioned requests account for 35 percent of the cost, and 18 percent of capacity sits idle, worth about $12K a month in recoverable savings.
If clusters dominate your bill, the Kubernetes Cost Management Guide and this node vs pod vs cluster explainer are the right starting points.
Clusters survive individual machine failures, scale by adding machines, and pack many workloads efficiently onto shared capacity.
The sum of its nodes plus the control plane fee and supporting services. Shared usage means per-team costs require allocation tooling.
Fewer, larger clusters pack more efficiently; more, smaller clusters isolate teams better. Most companies land on a handful per environment.