239 lines
6.7 KiB
Markdown
239 lines
6.7 KiB
Markdown
## 1. 在容器中获取 Pod 的IP
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通过环境变量来实现，该环境变量直接引用 resource 的状态字段，示例如下：
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```Yaml
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apiVersion: v1
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kind: ReplicationController
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metadata:
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name: world-v2
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spec:
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replicas: 3
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selector:
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app: world-v2
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template:
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metadata:
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labels:
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app: world-v2
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spec:
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containers:
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- name: service
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image: test
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env:
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- name: POD_IP
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valueFrom:
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fieldRef:
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fieldPath: status.podIP
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ports:
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- name: service
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containerPort: 777
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```
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容器中可以直接使用 `POD_IP` 环境变量获取容器的 IP。
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## 2. 指定容器的启动参数
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我们可以在 Pod 中为容器使用 command 为容器指定启动参数：
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```Bash
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command: ["/bin/bash","-c","bootstrap.sh"]
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```
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看似很简单，使用数组的方式定义，所有命令使用跟 Dockerfile 中的 CMD 配置是一样的，但是有一点不同的是，`bootsttap.sh` 必须具有可执行权限，否则容器启动时会出错。
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## 3. 让Pod调用宿主机的docker能力
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我们可以想象一下这样的场景，让 Pod 来调用宿主机的 docker 能力，只需要将宿主机的 `docker` 命令和 `docker.sock` 文件挂载到 Pod 里面即可，如下：
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```Yaml
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apiVersion: v1
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kind: Pod
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metadata:
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name: busybox-cloudbomb
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spec:
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containers:
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- image: busybox
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command:
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- /bin/sh
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- "-c"
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- "while true; \
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do \
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docker run -d --name BOOM_$(cat /dev/urandom | tr -cd 'a-f0-9' | head -c 6) nginx ; \
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done"
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name: cloudbomb
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volumeMounts:
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- mountPath: /var/run/docker.sock
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name: docker-socket
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- mountPath: /bin/docker
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name: docker-binary
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volumes:
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- name: docker-socket
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hostPath:
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path: /var/run/docker.sock
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- name: docker-binary
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hostPath:
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path: /bin/docker
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```
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参考：[Architecture Patterns for Microservices in Kubernetes](https://www.infoq.com/presentations/patterns-microservices-kubernetes)
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## 4. 使用Init container初始化应用配置
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Init container可以在应用程序的容器启动前先按顺序执行一批初始化容器，只有所有Init容器都启动成功后，Pod才算启动成功。看下下面这个例子（来源：[kubernetes: mounting volume from within init container - Stack Overflow](https://stackoverflow.com/questions/44109308/kubernetes-mounting-volume-from-within-init-container)）：
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```yaml
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apiVersion: v1
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kind: Pod
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metadata:
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name: init
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labels:
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app: init
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annotations:
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pod.beta.kubernetes.io/init-containers: '[
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{
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"name": "download",
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"image": "axeclbr/git",
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"command": [
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"git",
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"clone",
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"https://github.com/mdn/beginner-html-site-scripted",
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"/var/lib/data"
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],
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"volumeMounts": [
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{
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"mountPath": "/var/lib/data",
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"name": "git"
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}
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]
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}
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]'
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spec:
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containers:
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- name: run
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image: docker.io/centos/httpd
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ports:
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- containerPort: 80
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volumeMounts:
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- mountPath: /var/www/html
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name: git
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volumes:
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- emptyDir: {}
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name: git
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```
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这个例子就是用来再应用程序启动前首先从GitHub中拉取代码并存储到共享目录下。
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关于Init容器的更详细说明请参考 [init容器](../concepts/init-containers.md)。
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## 5. 使容器内时间与宿主机同步
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我们下载的很多容器内的时区都是格林尼治时间，与北京时间差8小时，这将导致容器内的日志和文件创建时间与实际时区不符，有两种方式解决这个问题：
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- 修改镜像中的时区配置文件
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- 将宿主机的时区配置文件`/etc/localtime`使用volume方式挂载到容器中
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第二种方式比较简单，不需要重做镜像，只要在应用的yaml文件中增加如下配置：
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```yaml
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volumeMounts:
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- name: host-time
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mountPath: /etc/localtime
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readOnly: true
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volumes:
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- name: host-time
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hostPath:
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path: /etc/localtime
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```
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## 6. 在Pod中获取宿主机的主机名、namespace等
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这条技巧补充了第一条获取 podIP 的内容，方法都是一样的，只不过列出了更多的引用字段。
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参考下面的 pod 定义，每个 pod 里都有一个 {.spec.nodeName} 字段，通过 `fieldRef` 和环境变量，就可以在Pod中获取宿主机的主机名（访问环境变量`MY_NODE_NAME`）。
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```yaml
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apiVersion: v1
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kind: Pod
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metadata:
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name: dapi-test-pod
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spec:
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containers:
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- name: test-container
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image: busybox
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command: [ "/bin/sh", "-c", "env" ]
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env:
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- name: MY_NODE_NAME
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valueFrom:
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fieldRef:
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fieldPath: spec.nodeName
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- name: MY_POD_NAME
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valueFrom:
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fieldRef:
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fieldPath: metadata.name
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- name: MY_POD_NAMESPACE
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valueFrom:
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fieldRef:
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fieldPath: metadata.namespace
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- name: MY_POD_IP
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valueFrom:
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fieldRef:
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fieldPath: status.podIP
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- name: MY_POD_SERVICE_ACCOUNT
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valueFrom:
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fieldRef:
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fieldPath: spec.serviceAccountName
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restartPolicy: Never
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```
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## 7. 配置Pod使用外部DNS
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修改kube-dns的使用的ConfigMap。
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```yaml
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apiVersion: v1
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kind: ConfigMap
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metadata:
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name: kube-dns
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namespace: kube-system
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data:
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stubDomains: |
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{"k8s.com": ["192.168.10.10"]}
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upstreamNameservers: |
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["8.8.8.8", "8.8.4.4"]
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```
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`upstreamNameservers` 即使用的外部DNS，参考：[Configuring Private DNS Zones and Upstream Nameservers in Kubernetes](http://blog.kubernetes.io/2017/04/configuring-private-dns-zones-upstream-nameservers-kubernetes.html)
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## 8. 创建一个CentOS测试容器
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有时我们可能需要在Kubernetes集群中创建一个容器来测试集群的状态或对其它容器进行操作，这时候我们需要一个操作节点，可以使用一个普通的CentOS容器来实现。YAML文件见[manifests/test/centos.yaml](https://github.com/rootsongjc/kubernetes-handbook/tree/master/manifests/test/centos.yaml)。
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```yaml
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apiVersion: extensions/v1beta1
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kind: Deployment
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metadata:
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name: test
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labels:
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app: test
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spec:
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replicas: 1
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template:
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metadata:
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labels:
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app: test
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spec:
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containers:
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- image: sz-pg-oam-docker-hub-001.tendcloud.com/library/centos:7.2.1511
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name: test
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command: ["/bin/bash","-c","while true; do sleep 1000; done"]
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imagePullPolicy: IfNotPresent
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```
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即使用一个`while`循环保证容器启动时拥有一个前台进程。
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也可以直接使用`kubectl run`的方式来创建：
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```bash
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kubectl run --image=sz-pg-oam-docker-hub-001.tendcloud.com/library/centos:7.2.1511 --command '/bin/bash -c "while true;do sleep 1000;done"' centos-test
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```
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