K8s之Pod資源管理（五）

pod是k8s管理的最小單元

pod中有多個容器，現實生產環境中只有一個容器

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特點:

1.最小部署單元
2.一組容器的集合
3.一個Pod中的容器共享網絡命令空間
4.Pod是短暫的

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Pod容器分類：

1：infrastructure container 基礎容器（透明的過程，用戶無感知）

維護整個Pod網絡空間

node節點操作

`查看容器的網絡`
[root@node1 ~]# cat /opt/kubernetes/cfg/kubelet
KUBELET_OPTS="--logtostderr=true \
--v=4 \
--hostname-override=192.168.18.148 \
--kubeconfig=/opt/kubernetes/cfg/kubelet.kubeconfig \
--bootstrap-kubeconfig=/opt/kubernetes/cfg/bootstrap.kubeconfig \
--config=/opt/kubernetes/cfg/kubelet.config \
--cert-dir=/opt/kubernetes/ssl \
--pod-infra-container-image=registry.cn-hangzhou.aliyuncs.com/google-containers/pause-amd64:3.0"	#提示網絡組件鏡像會從阿里雲上進行下載

`每次創建Pod時候就會創建，與Pod對應的，對於用戶是透明的`
[root@node1 ~]# docker ps
CONTAINER ID        IMAGE                                                                 COMMAND                  CREATED             STATUS              PORTS               NAMES
......此處省略多行
54d9e6ec3c02        registry.cn-hangzhou.aliyuncs.com/google-containers/pause-amd64:3.0   "/pause"
#網絡組件會被自動加載成一個組件提供出去
`結論：基礎容器在創建時，一定會去創建一個網絡容器`

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2：initcontainers 初始化容器

pod在進行創建時一定會被執行當中的初始化initcontainers，在老版本中執行時不會區分前後順序（在系統進行加載時PID號數字越小，優先級別越高，越先被啓動），隨着雲平臺的改進，啓動模式改爲主機形式，分隔出的初始化容器會被優先加載，在初始化容器加載完成之後後面的業務容器才能正常接着運行

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3：container 業務容器（並行啓動）

官方網站：https://kubernetes.io/docs/concepts/workloads/pods/init-containers/

示例：

Init containers in use

This example defines a simple Pod that has two init containers. The first waits for myservice, and the second waits for mydb. Once both init containers complete, the Pod runs the app container from its spec section.

apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
  labels:
    app: myapp
spec:
  containers:
  - name: myapp-container
    image: busybox:1.28
    command: ['sh', '-c', 'echo The app is running! && sleep 3600']
  initContainers:
  - name: init-myservice
    image: busybox:1.28
    command: ['sh', '-c', 'until nslookup myservice; do echo waiting for myservice; sleep 2; done;']
  - name: init-mydb
    image: busybox:1.28
    command: ['sh', '-c', 'until nslookup mydb; do echo waiting for mydb; sleep 2; done;']

鏡像拉取策略（image PullPolicy）

IfNotPresent：默認值，鏡像在宿主機上不存在時才拉取

Always：每次創建Pod都會重新拉取一次鏡像

Never：Pod永遠不會主動拉取這個鏡像

官方網站：https://kubernetes.io/docs/concepts/containers/images

示例：

Verify by creating a pod that uses a private image, e.g.:

kubectl apply -f - <<EOF
apiVersion: v1
kind: Pod
metadata:
  name: private-image-test-1
spec:
  containers:
    - name: uses-private-image
      image: $PRIVATE_IMAGE_NAME
      imagePullPolicy: Always
      command: [ "echo", "SUCCESS" ]
EOF

master1上操作

[root@master1 ~]# kubectl get pods
NAME                                READY   STATUS    RESTARTS   AGE
my-nginx-d55b94fd-kc2gl             1/1     Running   0          40h
my-nginx-d55b94fd-tkr42             1/1     Running   0          40h
nginx-6c94d899fd-8pf48              1/1     Running   0          2d15h
nginx-deployment-5477945587-f5dsm   1/1     Running   0          2d14h
nginx-deployment-5477945587-hmgd2   1/1     Running   0          2d14h
nginx-deployment-5477945587-pl2hn   1/1     Running   0          2d14h

[root@master1 ~]# kubectl edit deployment/my-nginx
......此處省略多行
    spec:
      containers:
      - image: nginx:1.15.4
        imagePullPolicy: IfNotPresent
        name: nginx
        ports:
        - containerPort: 80
          protocol: TCP
        resources: {}
        terminationMessagePath: /dev/termination-log
        terminationMessagePolicy: File
      dnsPolicy: ClusterFirst
      restartPolicy: Always
      schedulerName: default-scheduler
      securityContext: {}
      terminationGracePeriodSeconds: 30

[root@master1 ~]# cd demo/
[root@master1 demo]# vim pod1.yaml
apiVersion: v1
kind: Pod
metadata:
  name: mypod
spec:
  containers:
    - name: nginx
      image: nginx
      imagePullPolicy: Always
      command: [ "echo", "SUCCESS" ]
[root@master1 demo]# kubectl create -f pod1.yaml	#進行創建
pod/mypod created

此時會出現CrashLoopBackOff創建之後又關閉的狀態提示

`失敗的狀態的原因是因爲命令啓動衝突`
apiVersion: v1
kind: Pod
metadata:
  name: mypod
spec:
  containers:
    - name: nginx
      image: nginx:1.14		#同時更改一下版本nginx:1.14
      imagePullPolicy: Always
#刪除最後一行的command: [ "echo", "SUCCESS" ]語句

`刪除原有的資源`
[root@master1 demo]# kubectl delete -f pod1.yaml
pod "mypod" deleted

`更新資源`
[root@master1 demo]# kubectl apply -f pod1.yaml
pod/mypod created
[root@master1 demo]# kubectl get pods
NAME                                READY   STATUS    RESTARTS   AGE
mypod                               1/1     Running   0          3m26s

`查看分配節點`
[root@master1 demo]# kubectl get pods -o wide
NAME          READY   STATUS    RESTARTS   AGE     IP            NODE           NOMINATED NODE
mypod         1/1     Running   0          4m45s   172.17.40.5   192.168.18.145   <none>
#此時172.17.40.5段，對應的是node2節點的192.168.18.145地址

`到node2上查看指定的應用是否部署到指定節點上`
[root@node2 ~]# curl -I 172.17.40.5
HTTP/1.1 200 OK
Server: nginx/1.14.2
Date: Sat, 15 Feb 2020 04:11:53 GMT
Content-Type: text/html
Content-Length: 612
Last-Modified: Tue, 04 Dec 2018 14:44:49 GMT
Connection: keep-alive
ETag: "5c0692e1-264"
Accept-Ranges: bytes