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Kubernetes Pod

程序员文章站 2022-03-12 10:23:07
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1. 简介

Pod 是一个容器集合，且集合中的容器运行于同一台主机上。

同一个 Pod 中的多个容器共享相同的存储资源和网络资源。

Pod 是 Kubernetes 中最小的调度单元。

2. 基础用法

在线测试平台：minikube

pod.yaml：

apiVersion: v1
kind: Pod
metadata:
  name: nginx
  labels:
    app: nginx
    version: dev
spec:
  containers:
  - name: nginx
    image: nginx:1.14.2
    imagePullPolicy: IfNotPresent
    ports:
    - containerPort: 80

  • 创建

    $ kubectl apply -f pod.yaml
pod/nginx created

  • 罗列

    $ kubectl get pod
NAME    READY   STATUS    RESTARTS   AGE
nginx   1/1     Running   0          16s

  • 查看 Pod 的状态

    $ kubectl describe pod nginx
Name:         nginx
Namespace:    default
Priority:     0
Node:         minikube/172.17.0.123
Start Time:   Thu, 21 Oct 2021 12:36:10 +0000
Labels:       app=nginx
              version=dev
Annotations:  <none>
Status:       Running
IP:           172.18.0.6
IPs:
  IP:  172.18.0.6
Containers:
  nginx:
    Container ID:   docker://84e77377be124a9c768f1421edcf21f0304a728d93baf69206c7da6dcadd4346
    Image:          nginx:1.14.2
    Image ID:       docker-pullable://[email protected]:f7988fb6c02e0ce69257d9bd9cf37ae20a60f1df7563c3a2a6abe24160306b8d
    Port:           80/TCP
    Host Port:      0/TCP
    State:          Running
      Started:      Thu, 21 Oct 2021 12:36:18 +0000
    Ready:          True
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-lszb9 (ro)
Conditions:
  Type              Status
  Initialized       True 
  Ready             True 
  ContainersReady   True 
  PodScheduled      True 
Volumes:
  default-token-lszb9:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-lszb9
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
                 node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
Events:
  Type    Reason     Age    From               Message
  ----    ------     ----   ----               -------
  Normal  Scheduled  4m31s  default-scheduler  Successfully assigned default/nginx to minikube
  Normal  Pulling    4m29s  kubelet            Pulling image "nginx:1.14.2"
  Normal  Pulled     4m24s  kubelet            Successfully pulled image "nginx:1.14.2" in 5.718214559s
  Normal  Created    4m23s  kubelet            Created container nginx
  Normal  Started    4m23s  kubelet            Started container nginx

  • 在容器中执行指定的命令

    $ kubectl exec nginx -c nginx -it -- /bin/bash
[email protected]:/# ls
bin  boot  dev  etc  home  lib  lib64  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var

    第一个 nginx 是 Pod 名称，第二个 nginx 是 Pod 中容器的名称。

  • 查看容器的日志输出

    $ kubectl logs nginx -c nginx

  • 访问 nginx

    $ curl http://172.18.0.6
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
...
</html>

  • 删除

    $ kubectl delete pod nginx
pod "nginx" deleted

    或

    $ kubectl delete -f pod.yaml

3. 探针

Kubernetes 提供了 3 种类型的探针：

  • livenessProbe：指示容器是否在运行着。如果探测失败，则会杀死容器，然后根据重启策略来决定是否重启容器。
  • readinessProbe：指示容器是否准备好响应请求。
  • startupProbe：指示容器中的应用是否已经启动。如果启用了此类型的探针，则其他类型的探针会被禁用。

每种探针都提供了 3 种探测方法：

  • exec：在容器中执行指定的命令，如果命令退出码为 0，则认为是成功。
  • httpGet：向 Pod 发出一个 HTTP GET 请求，如果响应状态码位于 [200, 400) 之间，则认为是成功。
  • tcpSocket：向 Pod 发起一个 TCP 连接，如果指定的端口处于打开状态，则认为是成功。

例子：

  • exec 方式

    apiVersion: v1
kind: Pod
metadata:
  name: liveness-exec
spec:
  containers:
  - name: liveness
    image: k8s.gcr.io/busybox
    args:
    - /bin/sh
    - -c
    - touch /tmp/healthy; sleep 30; rm -rf /tmp/healthy; sleep 600
    livenessProbe:
      exec:
        command:
        - cat
        - /tmp/healthy
      initialDelaySeconds: 5
      periodSeconds: 5

  • httpGet 方式

    apiVersion: v1
kind: Pod
metadata:
  name: liveness-http
spec:
  containers:
  - name: liveness
    image: k8s.gcr.io/liveness
    args:
    - /server
    livenessProbe:
      httpGet:
        path: /healthz
        port: 8080
        httpHeaders:
        - name: Custom-Header
          value: Awesome
      initialDelaySeconds: 3
      periodSeconds: 3

  • tcpSocket 方式

    apiVersion: v1
kind: Pod
metadata:
  name: goproxy
spec:
  containers:
  - name: goproxy
    image: k8s.gcr.io/goproxy:0.1
    ports:
    - containerPort: 8080
    livenessProbe:
      tcpSocket:
        port: 8080
      initialDelaySeconds: 15
      periodSeconds: 20

4. 查看帮助

$ kubectl explain pod
KIND:     Pod
VERSION:  v1

DESCRIPTION:
     Pod is a collection of containers that can run on a host. This resource is
     created by clients and scheduled onto hosts.

FIELDS:
   apiVersion   <string>
     APIVersion defines the versioned schema of this representation of an
     object. Servers should convert recognized schemas to the latest internal
     value, and may reject unrecognized values. More info:
     https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#resources
   ...

$ kubectl explain pod.spec.containers
KIND:     Pod
VERSION:  v1

RESOURCE: containers <[]Object>

DESCRIPTION:
     List of containers belonging to the pod. Containers cannot currently be
     added or removed. There must be at least one container in a Pod. Cannot be
     updated.

     A single application container that you want to run within a pod.

FIELDS:
   args <[]string>
     Arguments to the entrypoint. The docker image's CMD is used if this is not
     provided. Variable references $(VAR_NAME) are expanded using the
     container's environment. If a variable cannot be resolved, the reference in
     the input string will be unchanged. The $(VAR_NAME) syntax can be escaped
     with a double $$, ie: $$(VAR_NAME). Escaped references will never be
     expanded, regardless of whether the variable exists or not. Cannot be
     updated. More info:
     https://kubernetes.io/docs/tasks/inject-data-application/define-command-argument-container/#running-a-command-in-a-shell
   ...
相关标签： 云计算 kubernetes pod kubectl

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