Difference between Control Plane and Data Plane in Kubernetes

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In Kubernetes, the terms "Control Plane" and "Data Plane" refer to two distinct sets of components that have different responsibilities in the cluster. Let's break down the differences:

Control Plane

The Control Plane's components make global decisions about the cluster (for example, scheduling), as well as detecting and responding to cluster events (like starting up a new pod when a deployment's replicas field is unsatisfied).

Components of the Control Plane include:

kube-apiserver: The API server is a component of the Kubernetes control plane that exposes the Kubernetes API. It is the entry point for commands sent via the kubectl CLI tool or other API clients.

etcd: Consistent and highly-available key-value store used as Kubernetes' backing store for all cluster data.

kube-scheduler: Watches for newly created Pods with no assigned node and selects a node for them to run on based on a variety of factors.

kube-controller-manager: Runs controller processes, which are background threads that handle routine tasks in the cluster. Examples include the Node Controller, Replication Controller, and Endpoints Controller.

cloud-controller-manager: Links the cluster into the cloud provider's API and separates out the components that interact with the cloud platform from those that just interact with the cluster.

Data Plane

The Data Plane consists of components that run your applications and workloads. It's where the actual compute, storage, and application-specific "data" operations occur.

Components of the Data Plane include:

kubelet: An agent that runs on each node in the cluster. It ensures that containers are running in a Pod.

kube-proxy: Maintains network rules on nodes that allow network communication to your Pods from network sessions inside or outside of your cluster.

Container runtime: Software responsible for running containers. Examples include Docker, containerd, and CRI-O.

In Summary:

Control Plane: Manages the cluster and maintains the desired state of the cluster.

Data Plane: Where the actual work, defined by the Control Plane, gets done. It's responsible for running your application workloads.

In essence, the Control Plane sets up and maintains the environment, while the Data Plane runs the actual applications within that environment.