Introduction
Ever wondered who actually starts, stops, and monitors containers on your Kubernetes node?
That’s the job of kubelet — the silent agent that lives on every node and makes sure containers are running as expected.
Let’s explore kubelet in a clear and friendly way.
What is kubelet?
kubelet is an agent that runs on each Kubernetes node. It talks to the control plane and makes sure the containers assigned to that node are healthy and running.
Think of kubelet as the local operations manager for your node.
What Does kubelet Do?
- Watches the API server for Pod specs
- Starts containers using container runtime (like containerd)
- Periodically checks container health
- Reports status back to the control plane
systemctl status kubelet
This shows the kubelet service on your node.
Pod Lifecycle Management
When you apply a manifest like this:
apiVersion: v1
kind: Pod
metadata:
name: my-app
spec:
containers:
- name: app
image: nginx
Here’s what happens:
- API server stores the spec
- Scheduler assigns it to a node
- kubelet on that node pulls the image and starts the container
Health Checks
kubelet runs liveness and readiness probes defined in your manifests:
livenessProbe:
httpGet:
path: /healthz
port: 8080
If a container fails the check, kubelet can restart it.
Communication with containerd
kubelet doesn’t directly manage containers — it talks to a container runtime like containerd or CRI-O.
crictl ps
Use this to inspect running containers managed by the runtime.
Why It’s Important
- Ensures pods are running
- Starts/stops containers
- Applies updates and probes
- Handles node-specific resource constraints
Summary
| Component | Role |
|---|---|
| kubelet | Manages pods on the node |
| containerd | Actually runs the containers |
| kube-apiserver | Sends instructions |
| kube-proxy | Handles networking |
Conclusion
kubelet may not be flashy, but it’s one of the hardest-working components in your cluster.
Without it, your containers would never run, restart, or report status. It’s the boots-on-the-ground agent that makes Kubernetes work.
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