Kubernetes controller
A Kubernetes controller is a control-loop component that observes resource state and takes action to move actual state toward desired state.
Kubernetes in Action, Second Edition
A Kubernetes controller is a control loop that observes cluster state and takes actions to move it toward a specified desired state.
- How it is used
- Keeps API-defined application resources aligned with their desired state as workloads are deployed, scaled, and maintained.
- How deep it goes
- Explains the reconciliation loop through ReplicaSet pod counts, selectors, ownership, and controller handoffs; stops short of controller implementation code.
- Examples
- Uses deleted and excess pods, a scaled Deployment, controller Events, and a failed readiness probe to show controller behavior and limits.
- What you can do after
- Diagnose/debug with it by checking why pods reappear, why an owned ReplicaSet change is reversed, and which controller acted.
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Kubernetes for Developers
A Kubernetes controller is a control-loop component that observes resource state and takes actions to move it toward the desired state.
- How it is used
- Uses declarative requirements to keep deployed workloads aligned with their intended state.
- How deep it goes
- Explains Deployment-driven Pod creation, replacement, and rescheduling, but does not detail controller implementation internals.
- Examples
- Demonstrates three replicas, container-version updates, eviction recovery, and the contrast between managed and direct Pods.
- What you can do after
- Operate/configure Deployments by declaring replica and container requirements, then applying YAML changes through Kubernetes.
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Related concepts
- StatefulSetcontrasts with · A StatefulSet is a Kubernetes workload resource that manages stateful Pods with stable identities, ordered operations, and persistent storage associations.
- podproduces · A Kubernetes Pod is the smallest deployable unit in Kubernetes, grouping one or more co-located containers that share networking and other resources.
- ReplicaSetuses · A ReplicaSet is a Kubernetes workload resource that maintains a specified number of Pods matching a defined Pod template.
- Kubernetespart of · Kubernetes is an open-source platform for orchestrating and automating the deployment, scaling, and management of containerized workloads across computing clusters.
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