242 lines
7.8 KiB
Markdown
242 lines
7.8 KiB
Markdown
---
|
|
reviewers:
|
|
- jsafrane
|
|
title: Create static Pods
|
|
weight: 170
|
|
content_template: templates/task
|
|
---
|
|
|
|
{{% capture overview %}}
|
|
|
|
|
|
*Static Pods* are managed directly by the kubelet daemon on a specific node,
|
|
without the {{< glossary_tooltip text="API server" term_id="kube-apiserver" >}}
|
|
observing them.
|
|
Unlike Pods that are managed by the control plane (for example, a
|
|
{{< glossary_tooltip text="Deployment" term_id="deployment" >}});
|
|
instead, the kubelet watches each static Pod (and restarts it if it crashes).
|
|
|
|
Static Pods are always bound to one {{< glossary_tooltip term_id="kubelet" >}} on a specific node.
|
|
|
|
The kubelet automatically tries to create a {{< glossary_tooltip text="mirror Pod" term_id="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.
|
|
|
|
{{< 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
|
|
{{< glossary_tooltip text="DaemonSet" term_id="daemonset" >}}
|
|
instead.
|
|
{{< /note >}}
|
|
|
|
{{% /capture %}}
|
|
|
|
{{% capture prerequisites %}}
|
|
|
|
{{< include "task-tutorial-prereqs.md" >}} {{< version-check >}}
|
|
|
|
This page assumes you're using {{< glossary_tooltip term_id="docker" >}} to run Pods,
|
|
and that your nodes are running the Fedora operating system.
|
|
Instructions for other distributions or Kubernetes installations may vary.
|
|
|
|
|
|
{{% /capture %}}
|
|
|
|
|
|
{{% capture steps %}}
|
|
|
|
## Create a static pod {#static-pod-creation}
|
|
|
|
You can configure a static Pod with either a [file system hosted configuration file](/docs/tasks/configure-pod-container/static-pod/#configuration-files) or a [web hosted configuration file](/docs/tasks/configure-pod-container/static-pod/#pods-created-via-http).
|
|
|
|
### Filesystem-hosted static Pod manifest {#configuration-files}
|
|
|
|
Manifests are standard Pod definitions in JSON or YAML format in a specific directory. Use the `staticPodPath: <the directory>` field in the [KubeletConfiguration file](/docs/tasks/administer-cluster/kubelet-config-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:
|
|
|
|
1. Choose a node where you want to run the static Pod. In this example, it's `my-node1`.
|
|
|
|
```shell
|
|
ssh my-node1
|
|
```
|
|
|
|
2. Choose a directory, say `/etc/kubelet.d` and place a web server Pod definition there, e.g. `/etc/kubelet.d/static-web.yaml`:
|
|
|
|
```shell
|
|
# 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
|
|
```
|
|
|
|
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 `/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 [KubeletConfiguration file](/docs/tasks/administer-cluster/kubelet-config-file).
|
|
|
|
4. Restart the kubelet. On Fedora, you would run:
|
|
|
|
```shell
|
|
# Run this command on the node where the kubelet is running
|
|
systemctl restart kubelet
|
|
```
|
|
|
|
### Web-hosted static pod manifest {#pods-created-via-http}
|
|
|
|
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](#configuration-files) 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.
|
|
|
|
```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
|
|
```
|
|
|
|
|
|
|
|
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:
|
|
|
|
```
|
|
KUBELET_ARGS="--cluster-dns=10.254.0.10 --cluster-domain=kube.local --manifest-url=<manifest-url>`
|
|
```
|
|
|
|
3. Restart the kubelet. On Fedora, you would run:
|
|
|
|
```shell
|
|
# Run this command on the node where the kubelet is running
|
|
systemctl restart kubelet
|
|
```
|
|
|
|
## Observe static pod behavior {#behavior-of-static-pods}
|
|
|
|
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):
|
|
```shell
|
|
# Run this command on the node where 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:
|
|
|
|
```shell
|
|
kubectl get pods
|
|
```
|
|
```
|
|
NAME READY STATUS RESTARTS AGE
|
|
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](/docs/concepts/policy/pod-security-policy/).
|
|
{{< /note >}}
|
|
|
|
|
|
{{< glossary_tooltip term_id="label" text="Labels" >}} from the static Pod are
|
|
propagated into the mirror Pod. You can use those labels as normal via
|
|
{{< glossary_tooltip term_id="selector" text="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:
|
|
|
|
```shell
|
|
kubectl delete pod static-web-my-node1
|
|
```
|
|
```
|
|
pod "static-web-my-node1" deleted
|
|
```
|
|
You can see that the Pod is still running:
|
|
```shell
|
|
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:
|
|
|
|
```shell
|
|
# 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 ...
|
|
```
|
|
|
|
## Dynamic addition and removal of static pods
|
|
|
|
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.
|
|
|
|
```shell
|
|
# 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
|
|
```
|
|
|
|
{{% /capture %}}
|