Reword & migrate static pod task page (#14831)
- Shape this to be more of a Task page - Move static pod task to pod & container sectionpull/15717/head
Tim Bannister
Kubernetes Prow Robot
parent
322e88de9a
commit
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@ -1,143 +0,0 @@
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---
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reviewers:
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- jsafrane
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title: Static Pods
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content_template: templates/concept
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---
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{{% capture overview %}}
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**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](/docs/concepts/workloads/controllers/daemonset/)!**
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*Static pods* are managed directly by kubelet daemon on a specific node, without the API server observing it. It does not have an associated replication controller, and kubelet daemon itself watches it and restarts it when it crashes. There is no health check. Static pods are always bound to one kubelet daemon and always run on the same node with it.
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Kubelet automatically tries to create a *mirror pod* on the Kubernetes API server for each static pod.
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This means that the pods are visible on the API server but cannot be controlled from there.
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{{% /capture %}}
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{{% capture body %}}
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## Static pod creation
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Static pod can be created in two ways: either by using configuration file(s) or by HTTP.
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### Configuration files
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The configuration files are just standard pod definitions in json or yaml format in a specific directory. Use `kubelet --pod-manifest-path=<the directory>` to start kubelet daemon or add 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.
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Note that kubelet will ignore files starting with dots when scanning the specified directory.
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For example, this is how to start a simple web server as a static pod:
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1. Choose a node where we want to run the static pod. In this example, it's `my-node1`.
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```
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[joe@host ~] $ ssh my-node1
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```
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2. Choose a directory, say `/etc/kubelet.d` and place a web server pod definition there, e.g. `/etc/kubelet.d/static-web.yaml`:
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```shell
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[root@my-node1 ~] $ mkdir /etc/kubelet.d/
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[root@my-node1 ~] $ cat <<EOF >/etc/kubelet.d/static-web.yaml
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apiVersion: v1
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kind: Pod
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metadata:
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name: static-web
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labels:
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role: myrole
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spec:
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containers:
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- name: web
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image: nginx
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ports:
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- name: web
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containerPort: 80
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protocol: TCP
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EOF
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```
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3. Configure your kubelet daemon on the node to use this directory by running it with `--pod-manifest-path=/etc/kubelet.d/` argument or add the `staticPodPath: <the directory>` field in the [KubeletConfiguration file](/docs/tasks/administer-cluster/kubelet-config-file).
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On Fedora edit `/etc/kubernetes/kubelet` to include this line:
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```
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KUBELET_ARGS="--cluster-dns=10.254.0.10 --cluster-domain=kube.local --pod-manifest-path=/etc/kubelet.d/"
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```
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Instructions for other distributions or Kubernetes installations may vary.
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4. Restart kubelet. On Fedora, this is:
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```
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[root@my-node1 ~] $ systemctl restart kubelet
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```
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### Pods created via HTTP
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Kubelet periodically downloads a file specified by `--manifest-url=<URL>` argument and interprets it as a json/yaml file with a pod definition. It works the same as `--pod-manifest-path=<directory>`, i.e. it's reloaded every now and then and changes are applied to running static pods (see below).
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## Behavior of static pods
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When kubelet starts, it automatically starts all pods defined in directory specified in `--pod-manifest-path=` or `--manifest-url=` arguments or add the `staticPodPath: <the directory>` field in the [KubeletConfiguration file](/docs/tasks/administer-cluster/kubelet-config-file), i.e. our static-web. (It may take some time to pull nginx image, be patient…):
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```shell
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[joe@my-node1 ~] $ docker ps
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CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
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f6d05272b57e nginx:latest "nginx" 8 minutes ago Up 8 minutes k8s_web.6f802af4_static-web-fk-node1_default_67e24ed9466ba55986d120c867395f3c_378e5f3c
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```
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If we look at our Kubernetes API server (running on host `my-master`), we see that a new mirror-pod was created there too:
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```shell
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[joe@host ~] $ ssh my-master
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[joe@my-master ~] $ kubectl get pods
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NAME READY STATUS RESTARTS AGE
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static-web-my-node1 1/1 Running 0 2m
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```
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Labels from the static pod are propagated into the mirror-pod and can be used as usual for filtering.
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Notice we cannot delete the pod with the API server (e.g. via [`kubectl`](/docs/user-guide/kubectl/) command), kubelet simply won't remove it.
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{{< note >}}
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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
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[PodSecurityPolicy](/docs/concepts/policy/pod-security-policy/).
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{{< /note >}}
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```shell
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[joe@my-master ~] $ kubectl delete pod static-web-my-node1
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pod "static-web-my-node1" deleted
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[joe@my-master ~] $ kubectl get pods
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NAME READY STATUS RESTARTS AGE
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static-web-my-node1 1/1 Running 0 12s
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```
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Back to our `my-node1` host, we can try to stop the container manually and see, that kubelet automatically restarts it in a while:
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```none
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[joe@host ~] $ ssh my-node1
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[joe@my-node1 ~] $ docker stop f6d05272b57e
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[joe@my-node1 ~] $ sleep 20
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[joe@my-node1 ~] $ docker ps
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CONTAINER ID IMAGE COMMAND CREATED ...
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5b920cbaf8b1 nginx:latest "nginx -g 'daemon of 2 seconds ago ...
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```
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## Dynamic addition and removal of static pods
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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.
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```shell
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[joe@my-node1 ~] $ mv /etc/kubelet.d/static-web.yaml /tmp
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[joe@my-node1 ~] $ sleep 20
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[joe@my-node1 ~] $ docker ps
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// no nginx container is running
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[joe@my-node1 ~] $ mv /tmp/static-web.yaml /etc/kubelet.d/
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[joe@my-node1 ~] $ sleep 20
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[joe@my-node1 ~] $ docker ps
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CONTAINER ID IMAGE COMMAND CREATED ...
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e7a62e3427f1 nginx:latest "nginx -g 'daemon of 27 seconds ago
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```
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{{% /capture %}}
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@ -0,0 +1,243 @@
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---
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reviewers:
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- jsafrane
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title: Create static Pods
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content_template: templates/task
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---
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{{% capture overview %}}
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*Static Pods* are managed directly by the kubelet daemon on a specific node,
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without the {{< glossary_tooltip text="API server" term_id="kube-apiserver" >}}
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observing them.
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Unlike Pods that are managed by the control plane (eg, a
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{{< glossary_tooltip text="Deployment" term_id="deployment" >}};
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instead, the kubelet watches each static Pod (and restarts it if it crashes).
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There are no health checks for the containers in a static Pod.
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Static Pods are always bound to one {{< glossary_tooltip term_id="kubelet" >}} on a specific node.
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Kubelet automatically tries to create a {{< glossary_tooltip text="mirror Pod" term_id="mirror-pod" >}}
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on the Kubernetes API server for each static Pod.
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This means that the Pods running on a node are visible on the API server,
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but cannot be controlled from there.
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{{< note >}}
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If you are running clustered Kubernetes and are using static
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Pods to run a Pod on every node, you should probably be using a
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{{< glossary_tooltip text="DaemonSet" term_id="daemonset" >}}
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instead.
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{{< /note >}}
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{{% /capture %}}
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{{% capture prerequisites %}}
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{{< include "task-tutorial-prereqs.md" >}} {{< version-check >}}
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This page assumes you're using {{< glossary_tooltip term_id="docker" >}} to run Pods,
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and that your nodes are running the Fedora operating system.
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Instructions for other distributions or Kubernetes installations may vary.
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{{% /capture %}}
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{{% capture steps %}}
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## Create a static pod {#static-pod-creation}
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You can configure a static Pod two different ways: either by using configuration file(s) or by HTTP.
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### Filesystem-hosted static Pod manifest {#configuration-files}
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The configuration files are just standard Pod definitions in JSON or YAML format in a specific directory. Use `kubelet --pod-manifest-path=<the directory>` to start the kubelet or add 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.
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Note that the kubelet will ignore files starting with dots when scanning the specified directory.
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For example, this is how to start a simple web server as a static Pod:
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1. Choose a node where you want to run the static Pod. In this example, it's `my-node1`.
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```shell
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ssh my-node1
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```
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2. Choose a directory, say `/etc/kubelet.d` and place a web server Pod definition there, e.g. `/etc/kubelet.d/static-web.yaml`:
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```shell
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# Run this command on the node where kubelet is running
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mkdir /etc/kubelet.d/
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cat <<EOF >/etc/kubelet.d/static-web.yaml
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apiVersion: v1
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kind: Pod
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metadata:
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name: static-web
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labels:
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role: myrole
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spec:
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containers:
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- name: web
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image: nginx
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ports:
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- name: web
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containerPort: 80
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protocol: TCP
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EOF
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```
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3. Configure your kubelet on the node to use this directory by running it with `--pod-manifest-path=/etc/kubelet.d/` argument or add the `staticPodPath: <the directory>` field in the [KubeletConfiguration file](/docs/tasks/administer-cluster/kubelet-config-file).
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On Fedora edit `/etc/kubernetes/kubelet` to include this line:
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```
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KUBELET_ARGS="--cluster-dns=10.254.0.10 --cluster-domain=kube.local --pod-manifest-path=/etc/kubelet.d/"
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```
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4. Restart the kubelet. On Fedora, you would run:
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```shell
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# Run this command on the node where the kubelet is running
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systemctl restart kubelet
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```
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### Web-hosted static pod manifest {#pods-created-via-http}
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Kubelet periodically downloads a file specified by `--manifest-url=<URL>` argument
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and interprets it as a JSON/YAML file that contains Pod definitions.
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Similar to how [filesystem-hosted manifests](#configuration-files) work, the kubelet
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refetches the manifest on a schedule. If there are changes to the list of static
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Pods, the kubelet applies them.
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If you want to use this approach, create a YAML file:
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```yaml
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apiVersion: v1
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kind: Pod
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metadata:
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name: static-web
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labels:
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role: myrole
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spec:
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containers:
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- name: web
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image: nginx
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ports:
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- name: web
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containerPort: 80
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protocol: TCP
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```
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and store it on a web server so that you can pass the URL of that file to the kubelet.
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Configure the kubelet on your selected node to use this web manifest by running it with `--manifest-url=<manifest-url>`
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On Fedora, edit `/etc/kubernetes/kubelet` to include this line:
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```
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KUBELET_ARGS="--cluster-dns=10.254.0.10 --cluster-domain=kube.local --manifest-url=<manifest-url>`
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```
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Now, restart the kubelet. On Fedora, you would run:
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```shell
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# Run this command on the node where the kubelet is running
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systemctl restart kubelet
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```
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## Observe static pod behavior {#behavior-of-static-pods}
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When the kubelet starts, it automatically starts all defined static Pods. As you have
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defined a static Pod and restarted the kubelet, the new static Pod should
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already be running.
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You can view running containers (including static Pods) by running (on the node):
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```shell
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# Run this command on the node where kubelet is running
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docker ps
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```
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The output might be something like:
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```
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CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
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f6d05272b57e nginx:latest "nginx" 8 minutes ago Up 8 minutes k8s_web.6f802af4_static-web-fk-node1_default_67e24ed9466ba55986d120c867395f3c_378e5f3c
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```
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You can see the mirror Pod on the API server:
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```shell
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kubectl get pods
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```
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```
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NAME READY STATUS RESTARTS AGE
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static-web-my-node1 1/1 Running 0 2m
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```
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{{< note >}}
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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
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[PodSecurityPolicy](/docs/concepts/policy/pod-security-policy/).
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{{< /note >}}
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{{< glossary_tooltip term_id="label" text="Labels" >}} from the static Pod are
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propagated into the mirror Pod. You can use those labels as normal via
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{{< glossary_tooltip term_id="selector" text="selectors" >}}, etc.
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If you try to use `kubectl` to delete the mirror Pod from the API server,
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the kubelet _doesn't_ remove the static Pod:
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```shell
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kubectl delete pod static-web-my-node1
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```
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```
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pod "static-web-my-node1" deleted
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```
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You can see that the Pod is still running:
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```shell
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kubectl get pods
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```
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```
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NAME READY STATUS RESTARTS AGE
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static-web-my-node1 1/1 Running 0 12s
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```
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Back on your node where the kubelet is running, you can try to stop the Docker
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container manually.
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You'll see that, after a time, the kubelet will notice and will restart the Pod
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automatically:
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```shell
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# Run these commands on the node where the kubelet is running
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docker stop f6d05272b57e # replace with the ID of your container
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sleep 20
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docker ps
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```
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```
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CONTAINER ID IMAGE COMMAND CREATED ...
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5b920cbaf8b1 nginx:latest "nginx -g 'daemon of 2 seconds ago ...
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```
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## Dynamic addition and removal of static pods
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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.
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```shell
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# This assumes you are using filesystem-hosted static Pod configuration
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# Run these commands on the node where the kubelet is running
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#
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mv /etc/kubelet.d/static-web.yaml /tmp
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sleep 20
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docker ps
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# You see that no nginx container is running
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mv /tmp/static-web.yaml /etc/kubelet.d/
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sleep 20
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docker ps
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```
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```
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CONTAINER ID IMAGE COMMAND CREATED ...
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e7a62e3427f1 nginx:latest "nginx -g 'daemon of 27 seconds ago
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```
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{{% /capture %}}
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@ -296,6 +296,7 @@
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/docs/tasks/administer-cluster/romana-network-policy/ /docs/tasks/administer-cluster/network-policy-provider/romana-network-policy/ 301
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/docs/tasks/administer-cluster/running-cloud-controller.md /docs/tasks/administer-cluster/running-cloud-controller/ 301
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/docs/tasks/administer-cluster/share-configuration/ /docs/tasks/access-application-cluster/configure-access-multiple-clusters/ 301
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/docs/tasks/administer-cluster/static-pod/ /docs/tasks/configure-pod-container/static-pod/ 301
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/docs/tasks/administer-cluster/upgrade-1-6/ /docs/tasks/administer-cluster/upgrade-downgrade/upgrade-1-6/ 301
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/docs/tasks/administer-cluster/weave-network-policy/ /docs/tasks/administer-cluster/network-policy-provider/weave-network-policy/ 301
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/docs/tasks/configure-pod-container/apply-resource-quota-limit/ /docs/tasks/administer-cluster/apply-resource-quota-limit/ 301
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|
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Reference in New Issue