Controller manager

Q: How deeply does Acing the Certified Kubernetes Administrator Exam, Second Edition cover controller manager?

Explains reconciliation and operational placement, then applies logs, manifests, and pod inspection to failure diagnosis without detailing controller internals.

As explained in Acing the Certified Kubernetes Administrator Exam, Second Edition

kube-controller-manager is the Kubernetes control-plane component that runs controller processes regulating cluster state.

The controller manager is a Kubernetes control-plane component that runs controllers responsible for matching observed cluster state to declared desired state. It regulates resources such as Deployments and ReplicaSets, creating or scaling pods when actual replicas differ from the requested count. section 1.5 section 2.1.2

Operationally, distinguish the controller manager from neighboring control-plane components:

Investigate the controller manager when a Deployment is not scaling correctly or its pods do not match the desired replica count. section 8.2
Find its system pod in the kube-system namespace on the control plane; control-plane components run as static pods described by manifests in /etc/kubernetes/manifests. section 2.1.2 section 8.2
Do not confuse it with the scheduler, which assigns pods to nodes, or the API server, which exposes the Kubernetes API. section 1.5 section 2.1.2

Diagnosing failed Deployment scaling

After creating prod-app with nginx, scale it from one to three replicas using kubectl scale deploy prod-app --replicas 3. If the two new pods remain Pending, inspect the control-plane components rather than the application container. Check the controller manager for reconciliation problems and the scheduler when pods cannot be assigned to nodes; inspect kube-system logs and describe output when a component is unhealthy. section 8.2

kubectl get po -o wide -A --field-selector spec.nodeName=kind-control-plane

Use the cluster-wide pod listing filtered by control-plane node to locate the controller manager alongside the other control-plane system pods. section 2.1.2

How Acing the Certified Kubernetes Administrator Exam, Second Edition covers it

Cover of Acing the Certified Kubernetes Administrator Exam, Second Edition

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Google Anthos in Actionkube-controller-manager is the Kubernetes control-plane component that runs controllers to reconcile cluster resources toward their desired state.

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Related concepts

control plane nodepart of · A control plane node is a Kubernetes cluster machine that hosts components managing cluster state, exposing the cluster API, scheduling workloads, and coordinating operations.
control loopuses · A control loop is a repeated process that observes a system’s state, compares it with a desired state, and uses feedback to guide corrective action.
control planepart of · A control plane is the management and coordination part of a system that governs the configuration, policies, state, and operations of its components and resources.
cloud controller managercontrasts with · The cloud controller manager is a Kubernetes control-plane component that runs controllers integrating cluster operation with an underlying cloud provider.
goaluses · A goal is a desired outcome or state that an actor or system aims to achieve and that can guide action or evaluation.
time zoneuses · A time zone is a geographic or rule-defined region whose local civil time is determined by offsets and calendar-time rules relative to a reference time standard.

This explainer was generated by Manning's knowledge graph from the text of Acing the Certified Kubernetes Administrator Exam, Second Edition. The section links point to the parts of the book it draws on.