controller-manager
- Docker & Kubernetes course
- Expert
- Lesson 3/47
- 4 min
Learn the controllers of kube-controller-manager.
controller-manager
kube-controller-manager runs dozens of controllers in a single process: the Deployment, ReplicaSet, StatefulSet, Job, Node, EndpointSlice, ServiceAccount and Namespace controllers... Each watches its own resource type and moves the actual state toward the desired state. For example:
- The Deployment controller creates ReplicaSets and adjusts their replicas.
- The ReplicaSet controller creates and deletes pods.
- The Node controller marks unresponsive nodes and has their pods evicted.
$ kubectl get pods -n kube-system -l component=kube-controller-manager
NAME READY STATUS
kube-controller-manager-control-plane 1/1 RunningLeader election
In highly available clusters, a controller-manager runs on each control-plane node, but only one is the leader at a time; the others wait. Leadership is held with a Lease object in kube-system and renewed regularly:
$ kubectl get lease -n kube-system kube-controller-manager -o jsonpath='{.spec.holderIdentity}'
cp-2_4f9a1c3e-…
$ kubectl get lease -n kube-systemThe same mechanism is used for kube-scheduler and for operators you write yourself.
Practice Find the leader
Write two commands: list the Lease objects in kube-system; print the holderIdentity value of the kube-controller-manager Lease with jsonpath='{.spec.holderIdentity}'.
Starter code
# buraya yazSample solution
kubectl get lease -n kube-system
kubectl get lease kube-controller-manager -n kube-system -o jsonpath='{.spec.holderIdentity}'Expected output
NAME HOLDER AGE kube-controller-manager cp-2_4f9a1c3e-… 12d kube-scheduler cp-1_9b2d7e4a-… 12d cp-2_4f9a1c3e-…
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What happens if a node hasn't responded for 5 minutes?
- The pods wait forever
- The node is deleted
- The node is marked NotReady and its pods are evicted and recreated on other nodes Correct answer
- The cluster stops
Explanation: The eviction delay is set with taints and tolerationSeconds.
2 List the leadership objects.
kubectl get ____ -n kube-systemkubectl get lease -n kube-systemExplanation: Lease objects are in the coordination.k8s.io group.
3 Match.
| Term | Meaning |
|---|---|
Deployment denetleyicisi |
Manages ReplicaSets |
ReplicaSet denetleyicisi |
Manages pods |
Node denetleyicisi |
Unresponsive nodes |
Lease |
Leader record |