Copy tasks/configure-pod-container/static-pod.md and glossary word files from en/ directory.
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TAKAHASHI Shuuji
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---
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title: Docker
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id: docker
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date: 2018-04-12
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full_link: https://docs.docker.com/engine/
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short_description: >
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Docker is a software technology providing operating-system-level virtualization also known as containers.
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aka:
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tags:
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- fundamental
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---
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Docker (specifically, Docker Engine) is a software technology providing operating-system-level virtualization also known as {{< glossary_tooltip text="containers" term_id="container" >}}.
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<!--more-->
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Docker uses the resource isolation features of the Linux kernel such as cgroups and kernel namespaces, and a union-capable file system such as OverlayFS and others to allow independent containers to run within a single Linux instance, avoiding the overhead of starting and maintaining virtual machines (VMs).
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---
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title: Mirror Pod
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id: mirror-pod
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date: 2019-08-06
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short_description: >
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An object in the API server that tracks a static pod on a kubelet.
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aka:
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tags:
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- fundamental
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---
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A {{< glossary_tooltip text="pod" term_id="pod" >}} object that a kubelet uses
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to represent a {{< glossary_tooltip text="static pod" term_id="static-pod" >}}
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<!--more-->
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When the kubelet finds a static pod in its configuration, it automatically tries to
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create a Pod object on the Kubernetes API server for it. This means that the pod
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will be visible on the API server, but cannot be controlled from there.
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(For example, removing a mirror pod will not stop the kubelet daemon from running it).
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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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weight: 170
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content_type: task
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---
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<!-- 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 (for example, 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 fails).
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Static Pods are always bound to one {{< glossary_tooltip term_id="kubelet" >}} on a specific node.
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The 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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## {{% heading "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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<!-- steps -->
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## Create a static pod {#static-pod-creation}
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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).
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### Filesystem-hosted static Pod manifest {#configuration-files}
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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](/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, for example `/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. 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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or add the `staticPodPath: <the directory>` field in the [kubelet configuration file](/docs/tasks/administer-cluster/kubelet-config-file).
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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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To use this approach:
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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.
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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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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:
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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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3. 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 the 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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