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Pod环境变量和initContainer
Pod环境变量
Pod中的环境变量主要有以下几种应用场景：
- 容器内应用程序获取Pod信息；
- 容器内应用程序通过用户定义的变量改变默认行为。
Pod环境变量可以按照以下方式定义：
- 自定义变量值；
- 变量值从Pod属性获取；
- 变量值从Secret、ConfigMap获取。
测试
生成测试用的yaml文件：[root@k8s-master ~]# kubectl run pod1 --image=busybox --dry-run=client -o yaml -- sleep 24 apiVersion: v1 kind: Pod metadata: creationTimestamp: null labels: run: pod1 name: pod1 spec: containers: - args: - sleep - "24" image: busybox name: pod1 resources: {} dnsPolicy: ClusterFirst restartPolicy: Always status: {}- 1
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通过
env属性手动定义变量、从Pod属性获取变量值：apiVersion: v1 kind: Pod metadata: labels: run: pod1 name: pod1 spec: containers: - args: - sleep - "24h" image: busybox name: pod1 env: #自定义变量 - name: testvar1 value: 42 - name: testvar2 value: KillerQueen - name: THIS_NODE_NAME #从Pod属性获取变量值 valueFrom: fieldRef: fieldPath: spec.nodeName - name: THIS_POD_NAME valueFrom: fieldRef: fieldPath: metadata.name - name: THIS_POD_NAMESPACE valueFrom: fieldRef: fieldPath: metadata.namespace - name: THIS_POD_IP valueFrom: fieldRef: fieldPath: status.podIP - name: THIS_POD_SRV_ACCOUNT valueFrom: fieldRef: fieldPath: spec.serviceAccountName- 1
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部署Pod：
[root@k8s-master ~]# kubectl apply -f pod1.yaml Error from server (BadRequest): error when creating "pod1.yaml": Pod in version "v1" cannot be handled as a Pod: json: cannot unmarshal number into Go struct field EnvVar.spec.containers.env.value of type string- 1
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将变量值为数字的加上引号，变为字符串：
env: #自定义变量 - name: testvar1 value: "42"- 1
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重新部署后，检查环境变量：
[root@k8s-master ~]# kubectl exec -it pod1 -- sh / # echo $testvar2 KillerQueen / # echo $THIS_NODE_NAME k8s-node2 / # echo $THIS_POD_NAME pod1 / # echo $THIS_POD_NAMESPACE default / # echo $THIS_POD_SRV_ACCOUNT default- 1
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initContainer
初始化容器（initContainer）仅用于同一个Pod中的业务容器运行前的初始化工作，执行完就结束。
- 优先于应用容器执行；
- 支持大部分应用容器配置，但不支持健康检查（lifecycle/livenessProbe/readinessProbe/startupProbe）。
主要应用场景包括：
- 环境检查：比如确保应用容器依赖的服务启动后再启动应用容器；
- 初始化配置：比如给应用准备配置文件。
测试
定义一个Pod，其中有两个初始化容器，一个等待myservice服务，另一个等待mydb服务。apiVersion: v1 kind: Pod metadata: name: myapp-pod labels: app.kubernetes.io/name: MyApp spec: containers: - name: myapp-container image: busybox:1.28 command: ['sh', '-c', 'echo The app is running! && sleep 3600'] initContainers: - name: init-myservice image: busybox:1.28 command: ['sh', '-c', "until nslookup myservice.$(cat /var/run/secrets/kubernetes.io/serviceaccount/namespace).svc.cluster.local; do echo waiting for myservice; sleep 2; done"] - name: init-mydb image: busybox:1.28 command: ['sh', '-c', "until nslookup mydb.$(cat /var/run/secrets/kubernetes.io/serviceaccount/namespace).svc.cluster.local; do echo waiting for mydb; sleep 2; done"]- 1
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运行Pod：
kubectl apply -f initConainer.yaml- 1
查看Pod创建状态：
[root@k8s-master ~]# kubectl get -f initContainer.yaml NAME READY STATUS RESTARTS AGE myapp-pod 0/1 Init:0/2 0 28s- 1
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或者
[root@k8s-master ~]# kubectl describe -f initContainer.yaml Name: myapp-pod Namespace: default Status: Pending ... Init Containers: init-myservice: Container ID: docker://667aa13dc8a9e8a1ecad54d88d0400c3d101e6946c1a41301ba6d9e66858b008 Image: busybox:1.28 ... State: Running Started: Sun, 31 Jul 2022 04:00:04 -0400 Ready: False ... init-mydb: Container ID: Image: busybox:1.28 Image ID: ... State: Waiting Reason: PodInitializing Ready: False ... Containers: myapp-container: Container ID: Image: busybox:1.28 Image ID: ... State: Waiting Reason: PodInitializing Ready: False ... Conditions: Type Status Initialized False Ready False ContainersReady False PodScheduled True Volumes: ... Events: Type Reason Age From Message ---- ------ ---- ---- ------- Normal Scheduled 3m40s default-scheduler Successfully assigned default/myapp-pod to k8s-node2 Normal Pulling 3m40s kubelet Pulling image "busybox:1.28" Normal Pulled 3m9s kubelet Successfully pulled image "busybox:1.28" in 30.987078455s Normal Created 3m9s kubelet Created container init-myservice Normal Started 3m9s kubelet Started container init-myservice- 1
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查看容器日志：
[root@k8s-master ~]# kubectl logs myapp-pod -c init-myservice nslookup: can't resolve 'myservice.default.svc.cluster.local' waiting for myservice [root@k8s-master ~]# kubectl logs myapp-pod -c init-mydb Error from server (BadRequest): container "init-mydb" in pod "myapp-pod" is waiting to start: PodInitializing- 1
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由于
myservice和mydb都未创建，init-myservice一直没有Ready，所以init-mydb一直在等待init-myservice就绪，而应用容器一直在等两个初始化容器就绪。接下来我们创建对应的服务：
--- apiVersion: v1 kind: Service metadata: name: myservice spec: ports: - protocol: TCP port: 80 targetPort: 9376 --- apiVersion: v1 kind: Service metadata: name: mydb spec: ports: - protocol: TCP port: 80 targetPort: 9377- 1
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暴露服务：
kubectl apply -f init-services.yaml- 1
再次查看应用状态：
[root@k8s-master ~]# kubectl get -f initContainer.yaml NAME READY STATUS RESTARTS AGE myapp-pod 1/1 Running 0 15m [root@k8s-master ~]# kubectl describe -f initContainer.yaml Name: myapp-pod Namespace: default ... Status: Running ... Init Containers: init-myservice: Container ID: docker://667aa13dc8a9e8a1ecad54d88d0400c3d101e6946c1a41301ba6d9e66858b008 ... State: Terminated Reason: Completed Exit Code: 0 Ready: True ... init-mydb: Container ID: docker://be037f56bdf5b2c940de7e0516b9167bf70674005fb64986aaed135c7e94d011 ... State: Terminated Reason: Completed Exit Code: 0 Ready: True ... Containers: myapp-container: Container ID: docker://0083db021fda9835ac7113c61f5a48403a91257b35c6866a9dfa84b8de57a46f ... State: Running Started: Sun, 31 Jul 2022 04:14:40 -0400 Ready: True Restart Count: 0 ... Conditions: Type Status Initialized True Ready True ContainersReady True PodScheduled True Volumes: ... Events: Type Reason Age From Message ---- ------ ---- ---- ------- Normal Scheduled 15m default-scheduler Successfully assigned default/myapp-pod to k8s-node2 Normal Pulling 15m kubelet Pulling image "busybox:1.28" Normal Pulled 15m kubelet Successfully pulled image "busybox:1.28" in 30.987078455s Normal Created 15m kubelet Created container init-myservice Normal Started 15m kubelet Started container init-myservice Normal Pulled 30s kubelet Container image "busybox:1.28" already present on machine Normal Created 30s kubelet Created container init-mydb Normal Started 29s kubelet Started container init-mydb Normal Pulled 29s kubelet Container image "busybox:1.28" already present on machine Normal Created 29s kubelet Created container myapp-container Normal Started 28s kubelet Started container myapp-container- 1
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总结
Pod中会有这几类容器：- 基础容器（Infrastructure Container）：维护整个Pod网络空间；
- 初始化容器（initContainer）：先于业务容器开始串行执行；
- 业务容器（Container） ：并行启动（Sidecar容器是从业务容器中分离出来的辅助容器）。
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- 原文地址：https://blog.csdn.net/Sebastien23/article/details/126088204
