Kubelet and kubectl are two essential components of the Kubernetes ecosystem, each serving distinct but interconnected roles.
Kubelet:
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Definition:
- Kubelet is an agent that runs on each node in a Kubernetes cluster. Its primary responsibility is to ensure that the containers running on the node are in the desired state, as defined by the Kubernetes control plane.
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Key Functions:
- Pod Lifecycle Management: Kubelet is responsible for starting, stopping, and maintaining the lifecycle of pods on its node. It communicates with the container runtime (e.g., Docker, containerd) to create and manage containers within pods.
- Health Checks: Kubelet regularly performs health checks on the containers it manages. If a container or pod is not healthy, Kubelet can take corrective actions, such as restarting the container.
- Resource Management: Kubelet ensures that containers have access to the necessary resources (CPU, memory) as specified in pod resource requests and limits.
- Image Management: Kubelet pulls container images as needed and ensures they are available for pod instantiation.
- Node Status: Kubelet reports the node’s status and resource usage to the Kubernetes control plane.
kubectl:
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Definition:
- kubectl (Kube Control) is the command-line tool used to interact with a Kubernetes cluster. It serves as the primary interface for administrators, developers, and operators to manage and control the cluster.
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Key Functions:
- Cluster Management: kubectl allows you to create, update, and delete Kubernetes resources like pods, services, deployments, and config maps.
- Resource Inspection: You can use kubectl to inspect the status and details of resources in the cluster, e.g., kubectl get pods, kubectl describe service.
- Scaling: kubectl enables you to scale deployments or replica sets up or down, e.g., kubectl scale deployment my-app –replicas=3.
- Resource Creation: You can create resources from YAML or JSON files using kubectl apply -f <file.yaml>.
- Pod Execution: You can execute commands inside pods using kubectl exec, access logs with kubectl logs, and copy files in and out of pods with kubectl cp.
- Interactivity: kubectl offers an interactive mode, where you can run a shell in a container using kubectl exec -it.
In summary, Kubelet is an agent running on each node that takes care of pod and container management on that node, while kubectl is the command-line tool used to manage and control the entire Kubernetes cluster from a centralized location. They work together to ensure that containerized workloads are orchestrated and maintained according to the desired configuration.