Create static Pods

    Static Pods are always bound to one Kubelet on a specific node.

    The kubelet automatically tries to create a on the Kubernetes API server for each static Pod. This means that the Pods running on a node are visible on the API server, but cannot be controlled from there. The Pod names will be suffixed with the node hostname with a leading hyphen.

    Note: If you are running clustered Kubernetes and are using static Pods to run a Pod on every node, you should probably be using a DaemonSet instead.

    Note: The of a static Pod cannot refer to other API objects (e.g., , ConfigMap, , etc).

    You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:

    To check the version, enter kubectl version.

    This page assumes you’re using to run Pods, and that your nodes are running the Fedora operating system. Instructions for other distributions or Kubernetes installations may vary.

    You can configure a static Pod with either a file system hosted configuration file or a .

    Manifests are standard Pod definitions in JSON or YAML format in a specific directory. Use the staticPodPath: <the directory> field in the kubelet configuration file, which periodically scans the directory and creates/deletes static Pods as YAML/JSON files appear/disappear there. Note that the kubelet will ignore files starting with dots when scanning the specified directory.

    1. Choose a node where you want to run the static Pod. In this example, it’s my-node1.

    2. Choose a directory, say /etc/kubelet.d and place a web server Pod definition there, for example /etc/kubelet.d/static-web.yaml:

      1. # Run this command on the node where kubelet is running
      2. mkdir /etc/kubelet.d/
      3. cat <<EOF >/etc/kubelet.d/static-web.yaml
      4. apiVersion: v1
      5. kind: Pod
      6. metadata:
      7.   name: static-web
      8.   labels:
      9.     role: myrole
      10. spec:
      11.   containers:
      12.     - name: web
      13.       image: nginx
      14.       ports:
      15.         - name: web
      16.           protocol: TCP
      17. EOF

    3. Configure your kubelet on the node to use this directory by running it with --pod-manifest-path=/etc/kubelet.d/ argument. On Fedora edit to include this line:

      1. KUBELET_ARGS="--cluster-dns=10.254.0.10 --cluster-domain=kube.local --pod-manifest-path=/etc/kubelet.d/"

      or add the staticPodPath: <the directory> field in the .

    4. Restart the kubelet. On Fedora, you would run:

      1. # Run this command on the node where the kubelet is running
      2. systemctl restart kubelet

    Web-hosted static pod manifest

    Kubelet periodically downloads a file specified by --manifest-url=<URL> argument and interprets it as a JSON/YAML file that contains Pod definitions. Similar to how work, the kubelet refetches the manifest on a schedule. If there are changes to the list of static Pods, the kubelet applies them.

    To use this approach:

    1. Create a YAML file and store it on a web server so that you can pass the URL of that file to the kubelet.

      1. apiVersion: v1
      2. kind: Pod
      3. metadata:
      4.   name: static-web
      5.   labels:
      6.     role: myrole
      7. spec:
      8.   containers:
      9.     - name: web
      10.       image: nginx
      11.       ports:
      12.         - name: web
      13.           containerPort: 80
      14.           protocol: TCP

    2. Configure the kubelet on your selected node to use this web manifest by running it with --manifest-url=<manifest-url>. On Fedora, edit /etc/kubernetes/kubelet to include this line:

      1. KUBELET_ARGS="--cluster-dns=10.254.0.10 --cluster-domain=kube.local --manifest-url=<manifest-url>"

    When the kubelet starts, it automatically starts all defined static Pods. As you have defined a static Pod and restarted the kubelet, the new static Pod should already be running.

    You can view running containers (including static Pods) by running (on the node):

    1. docker ps

    The output might be something like:

    2. f6d05272b57e nginx:latest  "nginx"  8 minutes ago  Up 8 minutes             k8s_web.6f802af4_static-web-fk-node1_default_67e24ed9466ba55986d120c867395f3c_378e5f3c

    You can see the mirror Pod on the API server:

    1. kubectl get pods
    1. NAME                       READY     STATUS    RESTARTS   AGE
    2. static-web-my-node1        1/1       Running   0          2m

    Note: Make sure the kubelet has permission to create the mirror Pod in the API server. If not, the creation request is rejected by the API server. See PodSecurityPolicy.

    from the static Pod are propagated into the mirror Pod. You can use those labels as normal via selectors, etc.

    If you try to use kubectl to delete the mirror Pod from the API server, the kubelet doesn’t remove the static Pod:

    1. kubectl delete pod static-web-my-node1

    You can see that the Pod is still running:

    1. kubectl get pods
    1. NAME                       READY     STATUS    RESTARTS   AGE
    2. static-web-my-node1        1/1       Running   0          12s

    Back on your node where the kubelet is running, you can try to stop the Docker container manually. You’ll see that, after a time, the kubelet will notice and will restart the Pod automatically:

    1. # Run these commands on the node where the kubelet is running
    2. docker stop f6d05272b57e # replace with the ID of your container
    3. sleep 20
    4. docker ps
    1. CONTAINER ID        IMAGE         COMMAND                CREATED       ...
    2. 5b920cbaf8b1        nginx:latest  "nginx -g 'daemon of   2 seconds ago ...
    1. # This assumes you are using filesystem-hosted static Pod configuration
    2. # Run these commands on the node where the kubelet is running
    3. #
    4. mv /etc/kubelet.d/static-web.yaml /tmp
    5. sleep 20
    6. docker ps
    7. # You see that no nginx container is running
    8. mv /tmp/static-web.yaml  /etc/kubelet.d/