Control Plane

A control plane manages the configuration and coordination that determine how a system should operate. It may decide which version should run, where work should be placed, and how much capacity is allocated. The data plane performs the application work governed by those decisions.

Desired state and running state

Suppose a recommendation service should run model v8 on three workers. Recording that desired configuration and coordinating workers belongs to control. Using a running worker to score a customer's products belongs to the data plane. A controller may repeatedly compare desired and observed state and act when they differ.

Kubernetes provides a concrete example: its control-plane components coordinate worker nodes and workloads. This illustrates responsibilities; a platform does not need Kubernetes or separate physical machines to use the distinction.

A configuration is not an enforcement result

An access policy may be managed centrally, while the query service enforces it for each request. Updating the policy alone is insufficient if a running service continues using an obsolete decision.

Control-plane failure may stop new deployments while existing requests continue. It may also disrupt requests that depend on live configuration or identity checks. Document those dependencies instead of assuming that all application work either stops or remains unaffected.

Reference: Kubernetes: Components.