K8s新手系列之Pod容器中的command和args指令

概述

command和args是containers下的两个指令，类似Dockerfile中的ENTRYPONIT和CMD指令。

官方文档地址：https://kubernetes.io/zh-cn/docs/tasks/inject-data-application/define-command-argument-container/

command

command功能同Dockerfile中的ENTRYPONIT指令，用于指定容器启动时要执行的命令。如果不设置command，容器将使用基础镜像中默认的启动命令，也就是ENTRYPONIT指定的启动命令。

可以通过kubectl explain pod.spec.containers.command查看对应的资源信息
示例：

[root@master01 ~]# kubectl explain pod.spec.containers.command KIND:     Pod VERSION:  v1  FIELD:    command <[]string>  DESCRIPTION:      Entrypoint array. Not executed within a shell. The container image's      ENTRYPOINT 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. Double $$      are reduced to a single $, which allows for escaping the $(VAR_NAME)      syntax: i.e. "$$(VAR_NAME)" will produce the string literal "$(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 

args

args功能同Dockerfile中的CMD指令，用于为command指定的命令提供参数。如果command没有指定，则args中的参数将作为基础镜像中默认命令的参数，也就是ENTRYPONIT指令的参数。

可以通过kubectl explain pod.spec.containers.args查看对应的资源信息
示例：

[root@master01 ~]# kubectl explain pod.spec.containers.args KIND:     Pod VERSION:  v1  FIELD:    args <[]string>  DESCRIPTION:      Arguments to the entrypoint. The container 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. Double $$ are reduced to a single $,      which allows for escaping the $(VAR_NAME) syntax: i.e. "$$(VAR_NAME)" will      produce the string literal "$(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 

示例

# 定义资源清单 [root@master01 ~/pod]# cat command-pod.yaml apiVersion: v1 kind: Pod metadata:   name: command-demo   labels:     purpose: demonstrate-command spec:   containers:   - name: command-demo-container     image: debian     command: ["printenv"]     args: ["HOSTNAME", "KUBERNETES_PORT"]   restartPolicy: OnFailure  # 创建pod [root@master01 ~/pod]# kubectl apply -f command-pod.yaml pod/command-demo created  # 查看Pod日志打印信息 [root@master01 ~/pod]# kubectl logs command-demo command-demo tcp://10.96.0.1:443 

使用注意事项

• 如果command和args均没有写，那么用Dockerfile的配置。

• 如果command写了，但args没有写，那么Dockerfile默认的配置会被忽略，执行输入的command

• 如果command没写，但args写了，那么Dockerfile中配置的ENTRYPOINT的命令会被执行，使用当前args的参数

• 如果command和args都写了，那么Dockerfile的配置被忽略，执行command并追加上args参数