Assigning remaining topics to TOC. Some deletions, combinations, and relegations to READMEs. Deactivating AnswerDash for now.
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John Mulhausen
@@ -137,14 +137,6 @@ a Daemon Set replaces pods that are deleted or terminated for any reason, such a
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node failure or disruptive node maintenance, such as a kernel upgrade. For this reason, you should
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use a Daemon Set rather than creating individual pods.
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### Static Pods
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It is possible to create pods by writing a file to a certain directory watched by Kubelet. These
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are called [static pods](/docs/admin/static-pods).
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Unlike DaemonSet, static pods cannot be managed with kubectl
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or other Kubernetes API clients. Static pods do not depend on the apiserver, making them useful
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in cluster bootstrapping cases. Also, static pods may be deprecated in the future.
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### Replication Controller
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Daemon Set are similar to [Replication Controllers](/docs/user-guide/replication-controller) in that
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+1
-1
@@ -22,7 +22,7 @@ to reduce downtime in case of corruption.
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## Default configuration
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The default setup scripts use kubelet's file-based static pods feature to run etcd in a
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The default setup scripts run etcd in a
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[pod](http://releases.k8s.io/{{page.githubbranch}}/cluster/saltbase/salt/etcd/etcd.manifest). This manifest should only
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be run on master VMs. The default location that kubelet scans for manifests is
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`/etc/kubernetes/manifests/`.
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@@ -51,7 +51,7 @@ Let's create two new namespaces to hold our work.
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Use the file [`namespace-dev.json`](/docs/admin/namespacesnamespace-dev.json) which describes a development namespace:
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{% include code.html language="json" file="namespace-dev.json" ghlink="https://github.com/kubernetes/kubernetes.github.io/blob/master/docs/admin/namespaces/namespace-dev.json" %}
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{% include code.html language="json" file="namespace-dev.json" ghlink="/docs/admin/namespaces/namespace-dev.json" %}
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Create the development namespace using kubectl.
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@@ -1,123 +0,0 @@
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---
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---
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**Static pods are to be deprecated and can be removed in any future Kubernetes release!**
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*Static pod* are managed directly by kubelet daemon on a specific node, without API server observing it. It does not have associated any replication controller, kubelet daemon itself watches it and restarts it when it crashes. There is no health check though. Static pods are always bound to one kubelet daemon and always run on the same node with it.
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Kubelet automatically creates so-called *mirror pod* on Kubernetes API server for each static pod, so the pods are visible there, but they cannot be controlled from the API server.
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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 definition in json or yaml format in specific directory. Use `kubelet --config=<the directory>` to start kubelet daemon, which periodically scans the directory and creates/deletes static pods as yaml/json files appear/disappear there.
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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-minion1`.
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```shell
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[joe@host ~] $ ssh my-minion1
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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/kubernetes.d/static-web.yaml`:
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```shell
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[root@my-minion1 ~] $ mkdir /etc/kubernetes.d/
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[root@my-minion1 ~] $ cat <<EOF >/etc/kubernetes.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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2. Configure your kubelet daemon on the node to use this directory by running it with `--config=/etc/kubelet.d/` argument. On Fedora Fedora 21 with Kubernetes 0.17 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 --config=/etc/kubelet.d/"
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```
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Instructions for other distributions or Kubernetes installations may vary.
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3. Restart kubelet. On Fedora 21, this is:
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```shell
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[root@my-minion1 ~] $ 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 `--config=<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 `--config=` or `--manifest-url=` arguments, 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-minion1 ~] $ docker ps
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CONTAINER ID IMAGE COMMAND CREATED STATUS NAMES
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f6d05272b57e nginx:latest "nginx" 8 minutes ago Up 8 minutes k8s_web.6f802af4_static-web-fk-minion1_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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POD IP CONTAINER(S) IMAGE(S) HOST LABELS STATUS CREATED MESSAGE
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static-web-my-minion1 172.17.0.3 my-minion1/192.168.100.71 role=myrole Running 11 minutes
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web nginx Running 11 minutes
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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/kubectl) command), kubelet simply won't remove it.
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```shell
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[joe@my-master ~] $ kubectl delete pod static-web-my-minion1
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pods/static-web-my-minion1
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[joe@my-master ~] $ kubectl get pods
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POD IP CONTAINER(S) IMAGE(S) HOST ...
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static-web-my-minion1 172.17.0.3 my-minion1/192.168.100.71 ...
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```
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Back to our `my-minion1` host, we can try to stop the container manually and see, that kubelet automatically restarts it in a while:
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```shell
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[joe@host ~] $ ssh my-minion1
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[joe@my-minion1 ~] $ docker stop f6d05272b57e
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[joe@my-minion1 ~] $ sleep 20
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[joe@my-minion1 ~] $ 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-minion1 ~] $ mv /etc/kubernetes.d/static-web.yaml /tmp
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[joe@my-minion1 ~] $ sleep 20
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[joe@my-minion1 ~] $ docker ps
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// no nginx container is running
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[joe@my-minion1 ~] $ mv /tmp/static-web.yaml /etc/kubernetes.d/
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[joe@my-minion1 ~] $ sleep 20
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[joe@my-minion1 ~] $ 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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