k8s集群namespace和context使用

落日映苍穹つ 2022-12-04 01:16 240阅读 0赞

### 1.kubeconfig文件 ###

使用 kubeconfig 文件来组织有关集群、用户、命名空间和身份认证机制的信息。kubectl 命令行工具使用 kubeconfig 文件来查找选择集群所需的信息，并与集群的 API 服务器进行通信。

注：用于配置集群访问的文件称为 kubeconfig 文件。这是引用配置文件的通用方法。这并不意味着有一个名为 kubeconfig 的文件

默认情况下，kubectl 在 $HOME/.kube 目录下查找名为 config 的文件。 您可以通过设置 KUBECONFIG 环境变量或者设置 --kubeconfig参数来指定其他 kubeconfig 文件。

k8s集群可以通过namespace和context的设置来对不同的工作组进行区分，使它们既可以共享同一个Kubernetes集群的服务，也能够互不干扰。

### 2. 上下文（Context） ###

通过 kubeconfig 文件中的 context 元素，使用简便的名称来对访问参数进行分组。每个上下文都有三个参数：cluster、namespace 和 user。默认情况下，kubectl 命令行工具使用 当前上下文 中的参数与集群进行通信。

kubectl config 命令可以设置和使用context

$ kubectl config --help

查看kubectl config命令的使用说明

Modify kubeconfig files using subcommands like "kubectl config set current-context my-context"
    
     The loading order follows these rules:
    
      1.  If the --kubeconfig flag is set, then only that file is loaded. The flag may only be set once and no merging takes
    place.
      2.  If $KUBECONFIG environment variable is set, then it is used as a list of paths (normal path delimiting rules for
    your system). These paths are merged. When a value is modified, it is modified in the file that defines the stanza. When
    a value is created, it is created in the first file that exists. If no files in the chain exist, then it creates the
    last file in the list.
      3.  Otherwise, ${HOME}/.kube/config is used and no merging takes place.
    
    Available Commands:
      current-context Displays the current-context
      delete-cluster  Delete the specified cluster from the kubeconfig
      delete-context  Delete the specified context from the kubeconfig
      get-clusters    Display clusters defined in the kubeconfig
      get-contexts    Describe one or many contexts
      rename-context  Renames a context from the kubeconfig file.
      set             Sets an individual value in a kubeconfig file
      set-cluster     Sets a cluster entry in kubeconfig
      set-context     Sets a context entry in kubeconfig
      set-credentials Sets a user entry in kubeconfig
      unset           Unsets an individual value in a kubeconfig file
      use-context     Sets the current-context in a kubeconfig file
      view            Display merged kubeconfig settings or a specified kubeconfig file
    
    Usage:
      kubectl config SUBCOMMAND [options]
    
    Use "kubectl <command> --help" for more information about a given command.
    Use "kubectl options" for a list of global command-line options (applies to all commands).

从以上我们看到kubectl config 命令可以设置、删除集群，设置、使用、删除上下文等操作。kubectl config view 用于显示合并的kubeconfig设置或指定的kubeconfig文件。

### namespace和context示例： ###

创建development(开发)和production(生产)两个namespace和context

***1）创建命名空间***

namespace-development.yaml

apiVersion: v1
    kind: Namespace
    metadata:
     name: development

namespace-production.yaml

apiVersion: v1
    kind: Namespace
    metadata:
     name: production

$ kubectl create -f namespace-development.yaml

$ kubectl create -f namespace-production.yaml

$ kubectl get namespaces

查看集群中的命名空间

***2）创建上下文***

创建ctx-dev上下文，指定其命名空间为development

$ kubectl config set-context ctx-dev --namespace=development --cluster=kubernetes --user=kubernetes-admin

创建ctx-prod上下文，指定其命名空间为production

$  kubectl config set-context ctx-prod --namespace=production --cluster=kubernetes --user=kubernetes-admin

注：--cluster=kubernetes --user=kubernetes-admin，cluster和user这里使用k8s集群本身的cluster和user，这样直接使用集群的密钥进行认证

$ kubectl config view

查看kubeconfig内容

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NraDIwMTVqYXZh_size_16_color_FFFFFF_t_70][]

从显示的信息中我们看到目前集群中有3个上下文，ctx-dev、ctx-prod和kubernetes-admin@kubernetes(k8s集群默认的上下文)。

从current-context看到当前的上下文为：kubernetes-admin@kubernetes

***上下文切换***

$ kubectl config use-context ctx-dev

![20200904182210653.png][]

在当前上下文创建一个RC

redis-slave-controller.yaml

apiVersion: v1
    kind: ReplicationController
    metadata:
     name: redis-slave
     labels:
      name: redis-slave
    spec:
     replicas: 2
     selector:
      name: redis-slave
     template:
      metadata:
       labels:
         name: redis-slave
      spec:
       containers:
       - name: slave
         image: kubeguide/guestbook-redis-slave
         ports:
         - containerPort: 6379

$ kubectl create -f redis-slave-controller.yaml

在当前上下文环境创建RC

$ kubectl get rc

查看对应的rc资源信息

![20200904182253802.png][]

切换到ctx-prod上下文

$ kubectl config use-context ctx-prod

![20200904182359948.png][]

查看当前上下文的资源信息

$ kubectl get rc

![20200904182820880.png][]

我们发现ctx-prod上下文环境中没有rc资源信息，所以在不同的上下文中，资源是相互隔离的，互不干扰。

context和kubeconfig的详细信息可参考官网：

[https://kubernetes.io/zh/docs/concepts/configuration/organize-cluster-access-kubeconfig/\#%E4%B8%8A%E4%B8%8B%E6%96%87-context][https_kubernetes.io_zh_docs_concepts_configuration_organize-cluster-access-kubeconfig_E4_B8_8A_E4_B8_8B_E6_96_87-context]

[https://kubernetes.io/zh/docs/tasks/access-application-cluster/configure-access-multiple-clusters/\#set-the-kubeconfig-environment-variable][https_kubernetes.io_zh_docs_tasks_access-application-cluster_configure-access-multiple-clusters_set-the-kubeconfig-environment-variable]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NraDIwMTVqYXZh_size_16_color_FFFFFF_t_70]: /images/20221123/28eabb7f547248d7b736cd4931460910.png
[20200904182210653.png]: /images/20221123/d78ee54e48f54078bc0b8f1690624333.png
[20200904182253802.png]: /images/20221123/49369d56ca1344819435973f08ad08ff.png
[20200904182359948.png]: /images/20221123/c6cb6e7933cb4852b98981e774e8e553.png
[20200904182820880.png]: /images/20221123/ab348d1fd81f400391e5ffd1599b052a.png
[https_kubernetes.io_zh_docs_concepts_configuration_organize-cluster-access-kubeconfig_E4_B8_8A_E4_B8_8B_E6_96_87-context]: https://kubernetes.io/zh/docs/concepts/configuration/organize-cluster-access-kubeconfig/#%E4%B8%8A%E4%B8%8B%E6%96%87-context
[https_kubernetes.io_zh_docs_tasks_access-application-cluster_configure-access-multiple-clusters_set-the-kubeconfig-environment-variable]: https://kubernetes.io/zh/docs/tasks/access-application-cluster/configure-access-multiple-clusters/#set-the-kubeconfig-environment-variable