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静态pod 创建使用示例详解

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一.系统环境

服务器版本docker软件版本Kubernetes(k8s)集群版本CPU架构
CentOS Linux release 7.4.1708 (Core)Docker version 20.10.12v1.21.9x86_64

Kubernetes集群架构：k8scloude1作为master节点，k8scloude2，k8scloude3作为worker节点

服务器操作系统版本CPU架构进程功能描述
k8scloude1/192.168.110.130CentOS Linux release 7.4.1708 (Core)x86_64docker，kube-apiserver，etcd，kube-scheduler，kube-controller-manager，kubelet，kube-proxy，coredns，calicok8s master节点
k8scloude2/192.168.110.129CentOS Linux release 7.4.1708 (Core)x86_64docker，kubelet，kube-proxy，calicok8s worker节点
k8scloude3/192.168.110.128CentOS Linux release 7.4.1708 (Core)x86_64docker，kubelet，kube-proxy，calicok8s worker节点

二.前言

本文介绍静态 Pod，静态 Pod 在指定的节点上由 kubelet 守护进程直接管理，不需要 API 服务器监管。

创建静态pod的前提是已经有一套可以正常运行的Kubernetes集群，关于Kubernetes(k8s)集群的安装部署，可以查看博客《Centos7 安装部署Kubernetes(k8s)集群》https:

三.静态pod

3.1 何为静态pod

静态 Pod 在指定的节点上由 kubelet 守护进程直接管理，不需要 API 服务器监管。 与由控制面管理的 Pod（例如，Deployment） 不同；kubelet 监视每个静态 Pod（在它失败之后重新启动）。静态 Pod 始终都会绑定到特定节点的 Kubelet 上。

kubelet 会尝试通过 Kubernetes API 服务器为每个静态 Pod 自动创建一个镜像 Pod。 这意味着节点上运行的静态 Pod 对 API 服务来说是可见的，但是不能通过 API 服务器来控制。 Pod 名称将把以连字符开头的节点主机名作为后缀。

说明：如果你在运行一个 Kubernetes 集群，并且在每个节点上都运行一个静态 Pod， 就可能需要考虑使用 DaemonSet 替代这种方式。静态 Pod 的 spec 不能引用其他 API 对象 （如：ServiceAccount、 ConfigMap、 Secret 等）。

3.2 创建静态pod

静态pod的应用场景为：1.使master能正常启动 2.如果某天我们的master崩溃了，如何让别人知道我们的服务器在维护？
目前该命名空间是没有pod运行的

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

静态pod的创建方法为：写一个yaml文件，然后把yaml文件放在指定目录，会自动根据yaml文件创建pod。有两种方法来指定这个目录：

--pod-manifest-path

/etc/kubernetes/manifests

3.2.1 使用--pod-manifest-path指定静态pod目录

查看kubelet的配置文件位置，可以看到kubelet的配置文件在/usr/lib/systemd/system/kubelet.service

注意：我们是在k8s集群的worker节点k8scloude2上创建静态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的配置文件/usr/lib/systemd/system/kubelet.service，使用--pod-manifest-path=/etc/kubernetes/kubelet.d指定静态pod目录。

[root@k8scloude2 ~]# vim /usr/lib/systemd/system/kubelet.service.d/10-kubeadm.conf 
#--pod-manifest-path=/etc/kubernetes/kubelet.d表示静态pod的目录为/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

创建静态pod目录，并使kubelet配置文件生效

[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...

进入静态pod的目录，然后创建pod yaml文件

[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集群的master节点上查看pod，在master上可以看到该pod，由于pod.yaml没有指定namespace，默认在default下，可以看到Pod 名称（pod-k8scloude2）是以连字符开头的节点主机名作为后缀。

[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>

当把这个pod.yaml文件从静态pod目录移走，pod就消失了

[root@k8scloude2 kubelet.d]# mv pod.yaml ~/
[root@k8scloude2 kubelet.d]# ls
#当把这个yaml文件移走,pod消失
[root@k8scloude1 pod]# kubectl get pods -n default -o wide
No resources found in default namespace.

现在指定静态pod的namespace为pod

[root@k8scloude2 kubelet.d]# vim pod.yaml 
#namespace: pod:指定pod的命名空间
[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

查看pod

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

3.2.2 静态pod默认目录/etc/kubernetes/manifests

注意：进行这一步的时候，先还原kubelet配置文件/usr/lib/systemd/system/kubelet.service.d/10-kubeadm.conf

查看配置文件，可以发现静态pod默认目录为/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
#默认的静态pod的目录为 ls /etc/kubernetes/manifests
[root@k8scloude2 kubelet.d]# ls /etc/kubernetes/manifests

在默认的静态pod目录/etc/kubernetes/manifests/下创建pod yaml文件

#namespace: pod:指定pod的命名空间
[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/

可以发现，静态pod已经创建了

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

删除yaml文件，静态pod消失

#删除yaml文件
[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.

前面几步，静态pod是在k8s集群的worker节点上做的，现在在k8s集群的master节点上做。

注意：如果在/usr/lib/systemd/system/kubelet.service.d/10-kubeadm.conf里添加了--pod-manifest-path=/etc/kubernetes/kubelet.d，则相应的/etc/kubernetes/manifests/下的yaml文件也要移动到/etc/kubernetes/kubelet.d目录下，不然k8s集群的master节点启动不起来。

可以看到k8s集群的master节点有很多静态pod。

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

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