一.系統環境

Kubernetes叢集架構：k8scloude1作為master節點，k8scloude2，k8scloude3作為worker節點

二.前言

本文介紹靜態 Pod，靜態 Pod 在指定的節點上由 kubelet 守護行程直接管理，不需要 API 伺服器監管。

建立靜態pod的前提是已經有一套可以正常執行的Kubernetes叢集，關於Kubernetes(k8s)叢集的安裝部署，可以檢視部落格《Centos7 安裝部署Kubernetes(k8s)叢集》https://www.cnblogs.com/renshengdezheli/p/16686769.html

三.靜態pod

3.1 何為靜態pod

靜態 Pod 在指定的節點上由 kubelet 守護行程直接管理，不需要 API 伺服器監管。 與由控制面管理的 Pod（例如，Deployment） 不同；kubelet 監視每個靜態 Pod（在它失敗之後重新啟動）。靜態 Pod 始終都會繫結到特定節點的 Kubelet 上。

kubelet 會嘗試通過 Kubernetes API 伺服器為每個靜態 Pod 自動建立一個映象 Pod。 這意味著節點上執行的靜態 Pod 對 API 服務來說是可見的，但是不能通過 API 伺服器來控制。 Pod 名稱將把以連字元開頭的節點主機名作為字尾。

說明：如果你在執行一個 Kubernetes 叢集，並且在每個節點上都執行一個靜態 Pod， 就可能需要考慮使用 DaemonSet 替代這種方式。靜態 Pod 的 spec 不能參照其他 API 物件 （如：ServiceAccount、 ConfigMap、 Secret 等）。

3.2 建立靜態pod

靜態pod的應用場景為：1.使master能正常啟動 2.如果某天我們的master崩潰了，如何讓別人知道我們的伺服器在維護？
目前該名稱空間是沒有pod執行的

[root@k8scloude1 pod]# kubectl get pods
No resources found in pod namespace.

靜態pod的建立方法為：寫一個yaml檔案，然後把yaml檔案放在指定目錄，會自動根據yaml檔案建立pod。有兩種方法來指定這個目錄：

1. --pod-manifest-path
2. /etc/kubernetes/manifests

3.2.1 使用--pod-manifest-path指定靜態pod目錄

檢視kubelet的組態檔位置，可以看到kubelet的組態檔在/usr/lib/systemd/system/kubelet.service

注意：我們是在k8s叢集的worker節點k8scloude2上建立靜態pod的

[root@k8scloude2 ~]# systemctl status kubelet
● kubelet.service - kubelet: The Kubernetes Node Agent
   Loaded: loaded (/usr/lib/systemd/system/kubelet.service; enabled; vendor preset: disabled)
  Drop-In: /usr/lib/systemd/system/kubelet.service.d
           └─10-kubeadm.conf
   Active: active (running) since 六 2022-01-15 12:27:34 CST; 5h 30min ago
     Docs: https://kubernetes.io/docs/
 Main PID: 947 (kubelet)
   Memory: 122.6M
   CGroup: /system.slice/kubelet.service
           └─947 /usr/bin/kubelet --bootstrap-kubeconfig=/etc/kubernetes/bootstrap-kubelet.conf --kubeconfig=/etc/kubernetes/kubelet.conf --config=/var/lib/kubelet/config.yaml --network-plugin=cni --pod-infr...

修改kubelet的組態檔/usr/lib/systemd/system/kubelet.service，使用--pod-manifest-path=/etc/kubernetes/kubelet.d指定靜態pod目錄。

[root@k8scloude2 ~]# vim /usr/lib/systemd/system/kubelet.service.d/10-kubeadm.conf 

#--pod-manifest-path=/etc/kubernetes/kubelet.d表示靜態pod的目錄為/etc/kubernetes/kubelet.d
[root@k8scloude2 ~]# cat /usr/lib/systemd/system/kubelet.service.d/10-kubeadm.conf
# Note: This dropin only works with kubeadm and kubelet v1.11+
[Service]
Environment="KUBELET_KUBECONFIG_ARGS=--bootstrap-kubeconfig=/etc/kubernetes/bootstrap-kubelet.conf --kubeconfig=/etc/kubernetes/kubelet.conf --pod-manifest-path=/etc/kubernetes/kubelet.d"
Environment="KUBELET_CONFIG_ARGS=--config=/var/lib/kubelet/config.yaml"
# This is a file that "kubeadm init" and "kubeadm join" generates at runtime, populating the KUBELET_KUBEADM_ARGS variable dynamically
EnvironmentFile=-/var/lib/kubelet/kubeadm-flags.env
# This is a file that the user can use for overrides of the kubelet args as a last resort. Preferably, the user should use
# the .NodeRegistration.KubeletExtraArgs object in the configuration files instead. KUBELET_EXTRA_ARGS should be sourced from this file.
EnvironmentFile=-/etc/sysconfig/kubelet
ExecStart=
ExecStart=/usr/bin/kubelet $KUBELET_KUBECONFIG_ARGS $KUBELET_CONFIG_ARGS $KUBELET_KUBEADM_ARGS $KUBELET_EXTRA_ARGS

建立靜態pod目錄，並使kubelet組態檔生效

[root@k8scloude2 ~]# mkdir /etc/kubernetes/kubelet.d

[root@k8scloude2 ~]# systemctl daemon-reload 

[root@k8scloude2 ~]# systemctl restart kubelet

[root@k8scloude2 ~]# systemctl status kubelet
● kubelet.service - kubelet: The Kubernetes Node Agent
   Loaded: loaded (/usr/lib/systemd/system/kubelet.service; enabled; vendor preset: disabled)
  Drop-In: /usr/lib/systemd/system/kubelet.service.d
           └─10-kubeadm.conf
   Active: active (running) since 六 2022-01-15 18:02:15 CST; 6s ago
     Docs: https://kubernetes.io/docs/
 Main PID: 108844 (kubelet)
   Memory: 30.7M
   CGroup: /system.slice/kubelet.service
           ├─108844 /usr/bin/kubelet --bootstrap-kubeconfig=/etc/kubernetes/bootstrap-kubelet.conf --kubeconfig=/etc/kubernetes/kubelet.conf --pod-manifest-path=/etc/kubernetes/kubelet.d --config=/var/lib/ku...
           └─108999 /usr/bin/kubelet --bootstrap-kubeconfig=/etc/kubernetes/bootstrap-kubelet.conf --kubeconfig=/etc/kubernetes/kubelet.conf --pod-manifest-path=/etc/kubernetes/kubelet.d --config=/var/lib/ku...

進入靜態pod的目錄，然後建立pod yaml檔案

[root@k8scloude2 ~]# cd /etc/kubernetes/kubelet.d/

[root@k8scloude2 kubelet.d]# ls

[root@k8scloude2 kubelet.d]# vim pod.yaml

[root@k8scloude2 kubelet.d]# cat pod.yaml 
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: pod
  name: pod
spec:
  containers:
  - image: nginx
    imagePullPolicy: IfNotPresent
    name: pod
    resources: {}
    ports:
    - name: http
      containerPort: 80
      protocol: TCP
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}

在k8s叢集的master節點上檢視pod，在master上可以看到該pod，由於pod.yaml沒有指定namespace，預設在default下，可以看到Pod 名稱（pod-k8scloude2）是以連字元開頭的節點主機名作為字尾。

[root@k8scloude1 pod]# kubectl get pods -n default -o wide
NAME             READY   STATUS    RESTARTS   AGE    IP               NODE         NOMINATED NODE   READINESS GATES
pod-k8scloude2   1/1     Running   0          109s   10.244.112.153   k8scloude2   <none>           <none>

當把這個pod.yaml檔案從靜態pod目錄移走，pod就消失了

[root@k8scloude2 kubelet.d]# mv pod.yaml ~/

[root@k8scloude2 kubelet.d]# ls

#當把這個yaml檔案移走,pod消失
[root@k8scloude1 pod]# kubectl get pods -n default -o wide
No resources found in default namespace.

現在指定靜態pod的namespace為pod

[root@k8scloude2 kubelet.d]# vim pod.yaml 

#namespace: pod:指定pod的名稱空間
[root@k8scloude2 kubelet.d]# cat pod.yaml 
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: pod
  name: pod
  namespace: pod
spec:
  containers:
  - image: nginx
    imagePullPolicy: IfNotPresent
    name: pod
    resources: {}
    ports:
    - name: http
      containerPort: 80
      protocol: TCP
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}

[root@k8scloude2 kubelet.d]# ls
pod.yaml

檢視pod

[root@k8scloude1 pod]# kubectl get pods -n pod
NAME             READY   STATUS    RESTARTS   AGE
pod-k8scloude2   1/1     Running   0          6s

3.2.2 靜態pod預設目錄/etc/kubernetes/manifests

注意：進行這一步的時候，先還原kubelet組態檔/usr/lib/systemd/system/kubelet.service.d/10-kubeadm.conf

檢視組態檔，可以發現靜態pod預設目錄為/etc/kubernetes/manifests

[root@k8scloude2 kubelet.d]# cat /usr/lib/systemd/system/kubelet.service.d/10-kubeadm.conf 
# Note: This dropin only works with kubeadm and kubelet v1.11+
[Service]
Environment="KUBELET_KUBECONFIG_ARGS=--bootstrap-kubeconfig=/etc/kubernetes/bootstrap-kubelet.conf --kubeconfig=/etc/kubernetes/kubelet.conf"
Environment="KUBELET_CONFIG_ARGS=--config=/var/lib/kubelet/config.yaml"
# This is a file that "kubeadm init" and "kubeadm join" generates at runtime, populating the KUBELET_KUBEADM_ARGS variable dynamically
EnvironmentFile=-/var/lib/kubelet/kubeadm-flags.env
# This is a file that the user can use for overrides of the kubelet args as a last resort. Preferably, the user should use
# the .NodeRegistration.KubeletExtraArgs object in the configuration files instead. KUBELET_EXTRA_ARGS should be sourced from this file.
EnvironmentFile=-/etc/sysconfig/kubelet
ExecStart=
ExecStart=/usr/bin/kubelet $KUBELET_KUBECONFIG_ARGS $KUBELET_CONFIG_ARGS $KUBELET_KUBEADM_ARGS $KUBELET_EXTRA_ARGS

[root@k8scloude2 kubelet.d]# ls /var/lib/kubelet/config.yaml
/var/lib/kubelet/config.yaml

[root@k8scloude2 kubelet.d]# cat /var/lib/kubelet/config.yaml | grep manifest
staticPodPath: /etc/kubernetes/manifests

#預設的靜態pod的目錄為 ls /etc/kubernetes/manifests
[root@k8scloude2 kubelet.d]# ls /etc/kubernetes/manifests

在預設的靜態pod目錄/etc/kubernetes/manifests/下建立pod yaml檔案

#namespace: pod:指定pod的名稱空間
[root@k8scloude2 kubelet.d]# vim ~/pod.yaml 

[root@k8scloude2 kubelet.d]# cat ~/pod.yaml 
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: pod
  name: pod
  namespace: pod
spec:
  containers:
  - image: nginx
    imagePullPolicy: IfNotPresent
    name: pod
    resources: {}
    ports:
    - name: http
      containerPort: 80
      protocol: TCP
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}

[root@k8scloude2 kubelet.d]# cp ~/pod.yaml /etc/kubernetes/manifests/

可以發現，靜態pod已經建立了

[root@k8scloude1 pod]# kubectl get pods -n pod
NAME             READY   STATUS    RESTARTS   AGE
pod-k8scloude2   1/1     Running   0          6s

刪除yaml檔案，靜態pod消失

#刪除yaml檔案
[root@k8scloude2 kubelet.d]# rm -rf /etc/kubernetes/manifests/pod.yaml 

#pod消失
[root@k8scloude1 pod]# kubectl get pods -n pod
No resources found in pod namespace.

前面幾步，靜態pod是在k8s叢集的worker節點上做的，現在在k8s叢集的master節點上做。

注意：如果在/usr/lib/systemd/system/kubelet.service.d/10-kubeadm.conf裡新增了--pod-manifest-path=/etc/kubernetes/kubelet.d，則相應的/etc/kubernetes/manifests/下的yaml檔案也要移動到/etc/kubernetes/kubelet.d目錄下，不然k8s叢集的master節點啟動不起來。

可以看到k8s叢集的master節點有很多靜態pod。

[root@k8scloude1 pod]# ls /etc/kubernetes/manifests/
etcd.yaml  kube-apiserver.yaml  kube-controller-manager.yaml  kube-scheduler.yaml