Static Pods are managed directly by the kubelet daemon on a specific node, without the API server observing them. Unlike Pods that are managed by the control plane (for example, a Deployment); instead, the kubelet watches each static Pod (and restarts it if it fails).
Static Pods are always bound to one Kubelet on a specific node.
The kubelet automatically tries to create a mirror Pod 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.
spec
of a static Pod cannot refer to other API objects (e.g., ServiceAccount, ConfigMap, Secret, 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, enterkubectl version
. This page assumes you're using Docker 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 web hosted configuration file.
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.
For example, this is how to start a simple web server as a static Pod:
Choose a node where you want to run the static Pod. In this example, it's my-node1
.
ssh my-node1
Choose a directory, say /etc/kubelet.d
and place a web server Pod definition there, for example /etc/kubelet.d/static-web.yaml
:
# Run this command on the node where kubelet is running
mkdir /etc/kubelet.d/
cat <<EOF >/etc/kubelet.d/static-web.yaml
apiVersion: v1
kind: Pod
metadata:
name: static-web
labels:
role: myrole
spec:
containers:
- name: web
image: nginx
ports:
- name: web
containerPort: 80
protocol: TCP
EOF
Configure your kubelet on the node to use this directory by running it with --pod-manifest-path=/etc/kubelet.d/
argument. On Fedora edit /etc/kubernetes/kubelet
to include this line:
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 kubelet configuration file.
Restart the kubelet. On Fedora, you would run:
# Run this command on the node where the kubelet is running
systemctl restart kubelet
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 filesystem-hosted manifests 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:
Create a YAML file and store it on a web server so that you can pass the URL of that file to the kubelet.
apiVersion: v1
kind: Pod
metadata:
name: static-web
labels:
role: myrole
spec:
containers:
- name: web
image: nginx
ports:
- name: web
containerPort: 80
protocol: TCP
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:
KUBELET_ARGS="--cluster-dns=10.254.0.10 --cluster-domain=kube.local --manifest-url=<manifest-url>"
Restart the kubelet. On Fedora, you would run:
# Run this command on the node where the kubelet is running
systemctl restart kubelet
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):
# Run this command on the node where the kubelet is running
docker ps
The output might be something like:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
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:
kubectl get pods
NAME READY STATUS RESTARTS AGE
static-web-my-node1 1/1 Running 0 2m
Labels 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:
kubectl delete pod static-web-my-node1
pod "static-web-my-node1" deleted
You can see that the Pod is still running:
kubectl get pods
NAME READY STATUS RESTARTS AGE
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:
# Run these commands on the node where the kubelet is running
docker stop f6d05272b57e # replace with the ID of your container
sleep 20
docker ps
CONTAINER ID IMAGE COMMAND CREATED ...
5b920cbaf8b1 nginx:latest "nginx -g 'daemon of 2 seconds ago ...
The running kubelet periodically scans the configured directory (/etc/kubelet.d
in our example) for changes and adds/removes Pods as files appear/disappear in this directory.
# This assumes you are using filesystem-hosted static Pod configuration
# Run these commands on the node where the kubelet is running
#
mv /etc/kubelet.d/static-web.yaml /tmp
sleep 20
docker ps
# You see that no nginx container is running
mv /tmp/static-web.yaml /etc/kubelet.d/
sleep 20
docker ps
CONTAINER ID IMAGE COMMAND CREATED ...
e7a62e3427f1 nginx:latest "nginx -g 'daemon of 27 seconds ago
© 2022 The Kubernetes Authors
Documentation Distributed under CC BY 4.0.
https://kubernetes.io/docs/tasks/configure-pod-container/static-pod/