Roles for Nodes in Kubernetes
This section describes the roles for etcd nodes, controlplane nodes, and worker nodes in Kubernetes, and how the roles work together in a cluster.
This diagram is applicable to Kubernetes clusters launched with Rancher using RKE..
^Lines show the traffic flow between components. Colors are used purely for visual aid^
etcd
Nodes with the etcd role run etcd, which is a consistent and highly available key value store used as Kubernetes’ backing store for all cluster data. etcd replicates the data to each node.
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Nodes with the |
controlplane
Nodes with the controlplane role run the Kubernetes master components (excluding etcd, as it’s a separate role). See Kubernetes: Master Components for a detailed list of components.
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Nodes with the |
kube-apiserver
The Kubernetes API server (kube-apiserver) scales horizontally. Each node with the role controlplane will be added to the NGINX proxy on the nodes with components that need to access the Kubernetes API server. This means that if a node becomes unreachable, the local NGINX proxy on the node will forward the request to another Kubernetes API server in the list.
kube-controller-manager
The Kubernetes controller manager uses leader election using an endpoint in Kubernetes. One instance of the kube-controller-manager will create an entry in the Kubernetes endpoints and updates that entry in a configured interval. Other instances will see an active leader and wait for that entry to expire (for example, when a node is unresponsive).
kube-scheduler
The Kubernetes scheduler uses leader election using an endpoint in Kubernetes. One instance of the kube-scheduler will create an entry in the Kubernetes endpoints and updates that entry in a configured interval. Other instances will see an active leader and wait for that entry to expire (for example, when a node is unresponsive).
worker
Nodes with the worker role run the Kubernetes node components. See Kubernetes: Node Components for a detailed list of components.