# Kubernetes 101 体验 Kubernetes 最简单的方法是跑一个 nginx 容器，然后使用 kubectl 操作该容器。Kubernetes 提供了一个类似于 `docker run` 的命令 `kubectl run`，可以方便的创建一个容器（实际上创建的是一个由 deployment 来管理的 Pod）： ```bash $ kubectl run --image=nginx:alpine nginx-app --port=80 deployment "nginx-app" created $ kubectl get pods NAME READY STATUS RESTARTS AGE nginx-app-4028413181-cnt1i 1/1 Running 0 52s ``` 等到容器变成 Running 后，就可以用 `kubectl` 命令来操作它了，比如 * `kubectl get` - 类似于 `docker ps`，查询资源列表 * `kubectl describe` - 类似于 `docker inspect`，获取资源的详细信息 * `kubectl logs` - 类似于 `docker logs`，获取容器的日志 * `kubectl exec` - 类似于 `docker exec`，在容器内执行一个命令 ```bash $ kubectl get pods NAME READY STATUS RESTARTS AGE nginx-app-4028413181-cnt1i 1/1 Running 0 6m $ kubectl exec nginx-app-4028413181-cnt1i -- ps aux USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1 0.0 0.5 31736 5108 ? Ss 00:19 0:00 nginx: master process nginx -g daemon off; nginx 5 0.0 0.2 32124 2844 ? S 00:19 0:00 nginx: worker process root 18 0.0 0.2 17500 2112 ? Rs 00:25 0:00 ps aux $ kubectl describe pod nginx-app-4028413181-cnt1i Name: nginx-app-4028413181-cnt1i Namespace: default Node: boot2docker/192.168.64.12 Start Time: Tue, 06 Sep 2016 08:18:41 +0800 Labels: pod-template-hash=4028413181 run=nginx-app Status: Running IP: 172.17.0.3 Controllers: ReplicaSet/nginx-app-4028413181 Containers: nginx-app: Container ID: docker://4ef989b57d0a7638ad9c5bbc22e16d5ea5b459281c77074fc982eba50973107f Image: nginx Image ID: docker://sha256:4efb2fcdb1ab05fb03c9435234343c1cc65289eeb016be86193e88d3a5d84f6b Port: 80/TCP State: Running Started: Tue, 06 Sep 2016 08:19:30 +0800 Ready: True Restart Count: 0 Environment Variables: Conditions: Type Status Initialized True Ready True PodScheduled True Volumes: default-token-9o8ks: Type: Secret (a volume populated by a Secret) SecretName: default-token-9o8ks QoS Tier: BestEffort Events: FirstSeen LastSeen Count From SubobjectPath Type Reason Message --------- -------- ----- ---- ------------- -------- ------ ------- 8m 8m 1 {default-scheduler} Normal Scheduled Successfully assigned nginx-app-4028413181-cnt1i to boot2docker 8m 8m 1 {kubelet boot2docker} spec.containers{nginx-app} Normal Pulling pulling image "nginx" 7m 7m 1 {kubelet boot2docker} spec.containers{nginx-app} Normal Pulled Successfully pulled image "nginx" 7m 7m 1 {kubelet boot2docker} spec.containers{nginx-app} Normal Created Created container with docker id 4ef989b57d0a 7m 7m 1 {kubelet boot2docker} spec.containers{nginx-app} Normal Started Started container with docker id 4ef989b57d0a $ curl http://172.17.0.3 Welcome to nginx!

Welcome to nginx!

If you see this page, the nginx web server is successfully installed and working. Further configuration is required.

For online documentation and support please refer to nginx.org.
Commercial support is available at nginx.com.

Thank you for using nginx.

$ kubectl logs nginx-app-4028413181-cnt1i 127.0.0.1 - - [06/Sep/2016:00:27:13 +0000] "GET / HTTP/1.0" 200 612 "-" "-" "-" ``` ## 使用 yaml 定义 Pod 上面是通过 `kubectl run` 来启动了第一个 Pod，但是 `kubectl run` 并不支持所有的功能。在 Kubernetes 中，更经常使用 yaml 文件来定义资源，并通过 `kubectl create -f file.yaml` 来创建资源。比如，一个简单的 nginx Pod 可以定义为： ```yaml apiVersion: v1 kind: Pod metadata: name: nginx labels: app: nginx spec: containers: - name: nginx image: nginx ports: - containerPort: 80 ``` 前面提到，`kubectl run` 并不是直接创建一个 Pod，而是先创建一个 Deployment 资源（replicas=1），再由与 Deployment 关联的 ReplicaSet 来自动创建 Pod，这等价于这样一个配置： ```yaml apiVersion: apps/v1 kind: Deployment metadata: labels: run: nginx-app name: nginx-app namespace: default spec: replicas: 1 selector: matchLabels: run: nginx-app strategy: rollingUpdate: maxSurge: 1 maxUnavailable: 1 type: RollingUpdate template: metadata: labels: run: nginx-app spec: containers: - image: nginx name: nginx-app ports: - containerPort: 80 protocol: TCP dnsPolicy: ClusterFirst restartPolicy: Always ``` ## 使用 Volume Pod 的生命周期通常比较短，只要出现了异常，就会创建一个新的 Pod 来代替它。那容器产生的数据呢？容器内的数据会随着 Pod 消亡而自动消失。Volume 就是为了持久化容器数据而生，比如可以为 redis 容器指定一个 hostPath 来存储 redis 数据： ```yaml apiVersion: v1 kind: Pod metadata: name: redis spec: containers: - name: redis image: redis volumeMounts: - name: redis-persistent-storage mountPath: /data/redis volumes: - name: redis-persistent-storage hostPath: path: /data/ ``` Kubernetes volume 支持非常多的插件，可以根据实际需要来选择： * emptyDir * hostPath * gcePersistentDisk * awsElasticBlockStore * nfs * iscsi * flocker * glusterfs * rbd * cephfs * gitRepo * secret * persistentVolumeClaim * downwardAPI * azureFileVolume * vsphereVolume ## 使用 Service 前面虽然创建了 Pod，但是在 kubernetes 中，Pod 的 IP 地址会随着 Pod 的重启而变化，并不建议直接拿 Pod 的 IP 来交互。那如何来访问这些 Pod 提供的服务呢？使用 Service。Service 为一组 Pod（通过 labels 来选择）提供一个统一的入口，并为它们提供负载均衡和自动服务发现。比如，可以为前面的 `nginx-app` 创建一个 service： ```yaml $ kubectl expose deployment nginx-app --port=80 --target-port=80 --type=NodePort service "nginx-app" exposed $ kubectl describe service nginx-app Name: nginx-app Namespace: default Labels: run=nginx-app Selector: run=nginx-app Type: ClusterIP IP: 10.0.0.66 Port: 80/TCP NodePort: 30772/TCP Endpoints: 172.17.0.3:80 Session Affinity: None No events. ``` 这样，在 cluster 内部就可以通过 `http://10.0.0.66` 和 `http://node-ip:30772` 来访问 nginx-app。而在 cluster 外面，则只能通过 `http://node-ip:30772` 来访问。 --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://kubernetes.feisky.xyz/introduction/101.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.