K8S實踐Ⅱ（Pod基本用法）

一、Static Pod

靜態Pod是由kubectl進行管理的僅存於特定Node上的Pod。其不能通過API Server進行管理，無法與ReplicationController、Deployment或者DaemonSet進行關聯，並且kubelet也無法對他們進行健康檢查。靜態Pod總是由kubectl進行創建，並且總是在kubelet所在的Node上運行。
創建靜態 Pod 有兩種方式：配置文件和 HTTP 兩種方式

由kubeadm安裝的集羣，對應的kubelet已經配置了靜態Pod文件的路徑

# cat /var/lib/kubelet/config.yaml |grep staticPodPath
staticPodPath: /etc/kubernetes/manifests

1.配置一個靜態Pod的yaml文件放入該路徑

# cat static-web.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: static-web
  labels:
    name: static-web
spec:
  containers:
  - name: static-web
    image: nginx
    ports:
    - name: web
      containerPort: 80

2.查看docker進程

# docker ps 
CONTAINER ID        IMAGE                   COMMAND                  CREATED             STATUS              PORTS               NAMES
b682d21563dd        nginx                   "nginx -g 'daemon of…"   6 minutes ago       Up 6 minutes                            k8s_static-web_static-web-k8s-2_default_a850d62a685464dd2c0bdb31222085c9_0

3.查看Pod創建情況

# kubectl get pod
NAME               READY   STATUS    RESTARTS   AGE
static-web-k8s-2   1/1     Running   0          7m14s

4.嘗試刪除該靜態Pod

[root@K8S-1 chapter1]# kubectl delete pod static-web-k8s-2
pod "static-web-k8s-2" deleted
[root@K8S-1 chapter1]# kubectl get pod
NAME               READY   STATUS    RESTARTS   AGE
static-web-k8s-2   0/1     Pending   0          1s
[root@K8S-1 chapter1]# kubectl get pod
NAME               READY   STATUS    RESTARTS   AGE
static-web-k8s-2   0/1     Pending   0          4s
[root@K8S-1 chapter1]# kubectl get pod
NAME               READY   STATUS    RESTARTS   AGE
static-web-k8s-2   1/1     Running   0          6s

5.刪除/etc/kubernetes/manifests下的yaml文件

# kubectl get pod
No resources found.

二、Pod容器共享Volume

同一個Pod裏面的多個容器能夠共享Pod級別的存儲卷Volume，Volume可以被定義爲各種類型，多個容器各自進行掛載操作，進行數據共享。

配置yaml文件

apiVersion: v1
kind: Pod
metadata:
  name: volume-pod
spec:
  containers:
  - name: tomcat
    image: tomcat
    ports:
    - containerPort: 8080
    volumeMounts:
    - name: app-logs
      mountPath: /usr/local/tomcat/logs
  - name: busybox
    image: busybox
    command: ["sh", "-c", "tail -f /logs/catalina*.log"]
    volumeMounts:
    - name: app-logs
      mountPath: /logs
  volumes:
  - name: app-logs
    emptyDir: {}

創建pod

# kubectl apply -f pod-volume-logs.yaml 
pod/volume-pod created

# kubectl get pod
NAME         READY   STATUS    RESTARTS   AGE
volume-pod   2/2     Running   0          4m42s

pod中有兩個容器，一個是tomcat用於寫入日誌文件，另一個busybox用於讀日誌文件

# kubectl logs volume-pod -c busybox
31-May-2019 16:54:39.573 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory [/usr/local/tomcat/webapps/docs] has finished in [26] ms
31-May-2019 16:54:39.573 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application directory [/usr/local/tomcat/webapps/examples]
31-May-2019 16:54:39.954 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory [/usr/local/tomcat/webapps/examples] has finished in [380] ms
31-May-2019 16:54:39.954 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application directory [/usr/local/tomcat/webapps/host-manager]
31-May-2019 16:54:39.992 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory [/usr/local/tomcat/webapps/host-manager] has finished in [38] ms
31-May-2019 16:54:39.992 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application directory [/usr/local/tomcat/webapps/manager]
31-May-2019 16:54:40.025 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory [/usr/local/tomcat/webapps/manager] has finished in [32] ms
31-May-2019 16:54:40.031 INFO [main] org.apache.coyote.AbstractProtocol.start Starting ProtocolHandler ["http-nio-8080"]
31-May-2019 16:54:40.045 INFO [main] org.apache.coyote.AbstractProtocol.start Starting ProtocolHandler ["ajp-nio-8009"]
31-May-2019 16:54:40.093 INFO [main] org.apache.catalina.startup.Catalina.start Server startup in 992 ms

# kubectl exec -it volume-pod -c tomcat -- ls /usr/local/tomcat/logs
catalina.2019-05-31.log      localhost_access_log.2019-05-31.txt
host-manager.2019-05-31.log  manager.2019-05-31.log
localhost.2019-05-31.log
# kubectl exec -it volume-pod -c tomcat -- tail /usr/local/tomcat/logs/catalina.2019-05-31.log
31-May-2019 16:54:39.573 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory [/usr/local/tomcat/webapps/docs] has finished in [26] ms
31-May-2019 16:54:39.573 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application directory [/usr/local/tomcat/webapps/examples]
31-May-2019 16:54:39.954 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory [/usr/local/tomcat/webapps/examples] has finished in [380] ms
31-May-2019 16:54:39.954 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application directory [/usr/local/tomcat/webapps/host-manager]
31-May-2019 16:54:39.992 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory [/usr/local/tomcat/webapps/host-manager] has finished in [38] ms
31-May-2019 16:54:39.992 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application directory [/usr/local/tomcat/webapps/manager]
31-May-2019 16:54:40.025 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory [/usr/local/tomcat/webapps/manager] has finished in [32] ms
31-May-2019 16:54:40.031 INFO [main] org.apache.coyote.AbstractProtocol.start Starting ProtocolHandler ["http-nio-8080"]
31-May-2019 16:54:40.045 INFO [main] org.apache.coyote.AbstractProtocol.start Starting ProtocolHandler ["ajp-nio-8009"]
31-May-2019 16:54:40.093 INFO [main] org.apache.catalina.startup.Catalina.start Server startup in 992 ms

三、Pod的應用配置管理ConfigMap

ConfigMap提供了將配置數據注入容器的機制，同時保持容器不受kubernetes的影響。ConfigMap有以下幾種使用方式：
1.生成容器內的環境變量
2.設置容器內的命令行參數
3.以Volume的形式掛載爲容器內部的文件或目錄
ConfigMap可以通過yaml配置文件或直接使用kubectl create configmap命令行方式來創建

1.從目錄創建

當--from-file指向一個目錄，該目錄中的文件名將直接用於填充ConfigMap中的key，key的值是這個文件的內容

# ls
my.cnf  web.xml

# cat my.cnf 
general_log=on
slow_query_log=on
long_query_time = 4
log_bin=on
log-bin=/usr/local/mysql/data/bin.log

# cat web.xml 
<?xml version="1.0" encoding="ISO-8859-1"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
                      http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
  version="3.0">
    <distributable/>
......
......
    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.htm</welcome-file>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
</web-app>

# kubectl create configmap test1 --from-file configfiles
configmap/test1 created

# kubectl describe configmap test1
Name:         test1
Namespace:    default
Labels:       <none>
Annotations:  <none>

Data
====
my.cnf:
----
general_log=on
slow_query_log=on
long_query_time = 4
log_bin=on
log-bin=/usr/local/mysql/data/bin.log

web.xml:
----
<?xml version="1.0" encoding="ISO-8859-1"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
                      http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
  version="3.0">
    <distributable/>
......
......
    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.htm</welcome-file>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
</web-app>

Events:  <none>

2.從文件創建

通過--from-file從文件創建，可以指定key的名稱，也可以在一個命令行中創建包含多個key的ConfigMap

# kubectl create configmap test2 --from-file=my.cnf --from-file=web.xml
configmap/test2 created

# kubectl get configmap test2 -o yaml
apiVersion: v1
data:
  my.cnf: |
    general_log=on
    slow_query_log=on
    long_query_time = 4
    log_bin=on
    log-bin=/usr/local/mysql/data/bin.log
  web.xml: |
    <?xml version="1.0" encoding="ISO-8859-1"?>
    <web-app xmlns="http://java.sun.com/xml/ns/javaee"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
                          http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
      version="3.0">
        <distributable/>
    ......
    ......
        <welcome-file-list>
            <welcome-file>index.html</welcome-file>
            <welcome-file>index.htm</welcome-file>
            <welcome-file>index.jsp</welcome-file>
        </welcome-file-list>
    </web-app>
kind: ConfigMap
metadata:
  creationTimestamp: "2019-06-01T10:49:09Z"
  name: test2
  namespace: default
  resourceVersion: "329312"
  selfLink: /api/v1/namespaces/default/configmaps/test2
  uid: e260c9aa-845a-11e9-a2f2-00505694834d

也可不以文件文件名爲key，通過key=value爲每個文件重新設置key

# kubectl create configmap test3 --from-file=the.cnf=my.cnf 
configmap/test3 created

# kubectl get configmap test3 -o yaml
apiVersion: v1
data:
  the.cnf: |
    general_log=on
    slow_query_log=on
    long_query_time = 4
    log_bin=on
    log-bin=/usr/local/mysql/data/bin.log
kind: ConfigMap
metadata:
  creationTimestamp: "2019-06-01T10:53:41Z"
  name: test3
  namespace: default
  resourceVersion: "329706"
  selfLink: /api/v1/namespaces/default/configmaps/test3
  uid: 849a9eab-845b-11e9-a2f2-00505694834d

3.使用--from-literal直接在命令行中指定key，value

# kubectl create configmap test4 --from-literal=type=null --from-literal=dir=/var/log
configmap/test4 created

# kubectl describe configmap test4
Name:         test4
Namespace:    default
Labels:       <none>
Annotations:  <none>

Data
====
dir:
----
/var/log
type:
----
null
Events:  <none>

4.通過環境變量方式使用ConfigMap

# cat cm-app.yaml 
apiVersion: v1
kind: ConfigMap
metadata:
  name: cm-app
data:
  apploglevel: info
  appdatadir: /var/data
# cat cm-env.yaml 
apiVersion: v1
kind: ConfigMap
metadata:
  name: cm-env
data:
  APPTYPE: char
# kubectl create -f cm-app.yaml -f cm-env.yaml 
configmap/cm-app created
configmap/cm-env created

# cat cm-test.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: cm-test
spec:
  containers:
    - name: test-container
      image: busybox
      command: [ "/bin/sh", "-c", "env | grep APP" ]
      env:
        - name: APPLOGLEVEL
          valueFrom:
            configMapKeyRef:
              name: cm-app
              key: apploglevel
        - name: APPDATADIR
          valueFrom:
            configMapKeyRef:
              name: cm-app
              key: appdatadir
      envFrom:
        - configMapRef:
            name: cm-env
  restartPolicy: Never

# kubectl create -f cm-test.yaml 
pod/cm-test created
# kubectl logs cm-test
APPDATADIR=/var/data
APPTYPE=char
APPLOGLEVEL=info

上面使用了兩種定義環境變量的方式：env和envFrom，使用envFrom會在Pod環境中將ConfigMap中所有定義的key=value自動生成爲環境變量

5.通過volumeMount使用ConfigMap

# cat cm-app.yaml 
apiVersion: v1
kind: ConfigMap
metadata:
  name: cm-app
data:
  apploglevel: info
  appdatadir: /var/data

# cat cm-volume.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: cm-volume
spec:
  containers:
    - name: cm-volume
      image: busybox
      command: [ "/bin/sh","-c","cat /etc/config/path/key.app" ]
      volumeMounts:
      - name: volume-test             #引用volume的名稱
        mountPath: /etc/config       #掛載到容器內的目錄
  volumes:
    - name: volume-test               #定義volume的名稱
      configMap:
        name: cm-app                    #使用的ConfigMap
        items:
        - key: apploglevel
          path: path/key.app           #value將寫入key.app文件中
  restartPolicy: Never

創建完ConfigMap和Pod後，該Pod會輸出：

# kubectl logs cm-volume
info

如果在引用ConfigMap時不指定items，則使用volumeMounts方式在容器內的目錄下爲每個items都生成一個以key開頭的文件。

使用ConfigMap的限制條件：

ConfigMap必須在Pod之前創建

ConfigMap受Namespace限制，只有處於相同Namespace中的Pod才能引用

靜態Pod無法引用ConfigMap

四、獲取容器內Pod信息 Downward API

      env:
        - name: MY_NODE_NAME
          valueFrom:
            fieldRef:
              fieldPath: spec.nodeName
        - name: MY_POD_NAME
          valueFrom:
            fieldRef:
              fieldPath: metadata.name
        - name: MY_POD_NAMESPACE
          valueFrom:
            fieldRef:
              fieldPath: metadata.namespace
        - name: MY_POD_IP
          valueFrom:
            fieldRef:
              fieldPath: status.podIP
        - name: MY_POD_SERVICE_ACCOUNT
          valueFrom:
            fieldRef:
              fieldPath: spec.serviceAccountName

五、Pod狀態和健康檢查

1.Pod的狀態

掛起（Pending）：API Server已經創建該Pod，但在Pod內還有一個或多個容器的鏡像沒有創建，包括正在下載的過程

運行中（Running）：Pod內所有容器均已創建，且至少有一個容器處於運行、啓動、重啓狀態

成功（Succeeded）：Pod 中的所有容器都被成功執行後退出，並且不會再重啓

失敗（Failed）：Pod 中的所有容器都已終止了，但至少有一個容器退出爲失敗狀態，也就是說，容器以非0狀態退出或者被系統終止。

未知（Unknown）：因爲某些原因無法取得 Pod 的狀態，通常是因爲與 Pod 所在主機通信失敗

2.Pod的重啓策略

Pod的重啓策略RestartPolicy可能的值爲 Always、OnFailure 和 Never，默認爲 Always

Always：當容器失效時，由kubelet自動重啓

OnFailure：當容器終止運行且退出碼不爲0時，由kubelet自動重啓

Never：不論容器運行狀態如何都不會重啓

3.Pod健康檢查

LivenessProbe：存活性探測
ReadnessProbe：就緒性探測
其存活性探測的方法可配置以下三種實現方式：

ExecAction：在容器內執行指定命令。如果命令退出時返回碼爲 0 則表明容器健康

TCPSocketAction：對指定端口上的容器的 IP 地址進行 TCP 檢查。如果能夠建立連接，則表明容器健康。

HTTPGetAction：對指定的端口和路徑上的容器的 IP 地址執行 HTTP Get 請求。如果響應的狀態碼大於等於200 且小於 400則表明容器健康

設置exec探針

# cat pod-exec.yaml 
apiVersion: v1
kind: Pod
metadata:
  labels:
    test: liveness
  name: liveness-exec
spec:
  containers:
  - name: liveness
    image: busybox
    args:
    - /bin/sh
    - -c
    - echo ok > /tmp/health; sleep 10; rm -rf /tmp/health; sleep 600
    livenessProbe:
      exec:
        command:
        - cat
        - /tmp/health
      initialDelaySeconds: 15
      timeoutSeconds: 1

查看Pod事件

# kubectl describe pod liveness-exec

  Type     Reason     Age                  From               Message
  ----     ------     ----                 ----               -------
  Normal   Scheduled  4m10s                default-scheduler  Successfully assigned default/liveness-exec to k8s-2
  Normal   Pulled     77s (x3 over 3m59s)  kubelet, k8s-2     Successfully pulled image "busybox"
  Normal   Created    76s (x3 over 3m59s)  kubelet, k8s-2     Created container liveness
  Normal   Started    76s (x3 over 3m59s)  kubelet, k8s-2     Started container liveness
  Warning  Unhealthy  35s (x9 over 3m35s)  kubelet, k8s-2     Liveness probe failed: cat: can't open '/tmp/health': No such file or directory
  Normal   Killing    35s (x3 over 3m15s)  kubelet, k8s-2     Container liveness failed liveness probe, will be restarted
  Normal   Pulling    5s (x4 over 4m10s)   kubelet, k8s-2     Pulling image "busybox"

# kubectl get pod
NAME            READY   STATUS    RESTARTS   AGE
liveness-exec   1/1     Running   3          4m50s
#此時restart值爲3

設置tcp探針

apiVersion: v1
kind: Pod
metadata:
  name: pod-with-healthcheck
spec:
  containers:
  - name: nginx
    image: nginx
    ports:
    - containerPort: 80
    livenessProbe:
      tcpSocket:
        port: 80
      initialDelaySeconds: 30
      timeoutSeconds: 1

設置http探針

apiVersion: v1
kind: Pod
metadata:
  name: pod-with-healthcheck
spec:
  containers:
  - name: nginx
    image: nginx
    ports:
    - containerPort: 80
    livenessProbe:
      httpGet:
        path: /_status/healthz
        port: 80
      initialDelaySeconds: 30
      timeoutSeconds: 1

  Type     Reason     Age                  From               Message
  ----     ------     ----                 ----               -------
  Normal   Scheduled  2m37s                default-scheduler  Successfully assigned default/liveness-http to k8s-2
  Warning  Unhealthy  14s (x6 over 104s)   kubelet, k8s-2     Liveness probe failed: HTTP probe failed with statuscode: 404
  Normal   Killing    14s (x2 over 84s)    kubelet, k8s-2     Container nginx failed liveness probe, will be restarted
  Normal   Pulling    13s (x3 over 2m36s)  kubelet, k8s-2     Pulling image "nginx"
  Normal   Pulled     5s (x3 over 2m19s)   kubelet, k8s-2     Successfully pulled image "nginx"
  Normal   Created    5s (x3 over 2m18s)   kubelet, k8s-2     Created container nginx
  Normal   Started    5s (x3 over 2m18s)   kubelet, k8s-2     Started container nginx

# kubectl get pod
NAME            READY   STATUS    RESTARTS   AGE
liveness-http   1/1     Running   2          3m31s

對於每種探測方式，需要設置initialDelaySeconds和timeoutSeconds參數，分別表示首次檢查等待時間以及超時時間。

K8S實踐Ⅱ（Pod基本用法）

一、Static Pod

二、Pod容器共享Volume

三、Pod的應用配置管理ConfigMap

四、獲取容器內Pod信息 Downward API

五、Pod狀態和健康檢查

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