Kubernetes 学习5 kubernetes资源清单定义入门

一、kubernetes是有一个restful风格的 API，把各种操作对象都一律当做资源来管理。并且可通过标准的HTTP请求的方法 GET，PUT，DELETE，POST，等方法来完成操作，不过是通过相应的命令反馈在kubectl 之上，如kubectl run，get，edit，...。

二、k8s常用的资源实例化后我们称之为对象。k8s相关的核心资源如下。

　　1、workload(工作负载型资源对象)：Pod，ReplicaSet，Deployment，StatefulSet，DaemonSet，Job,Cronjob...

　　2、Service，Ingress 服务发现和负载均衡有关 ....

　　3、Volume 配置与存储。 现在的k8s版本还支持基于CSI，容器存储接口来支持各种各样的存储卷。我们还有另外两种特殊类型的存储卷。

　　　　a、ConfigMap ：用来当配置中心使用的资源

　　　　b、Secret：和ConfigMap 功能相同但是用来保存敏感数据。

　　　　c、DownwardAPI：把外部环境中的信息输出给容器

　　4、集群级的资源

　　　　a、Namespace，Node，Role(名称空间级的资源),ClusterRole，RoleBinding，ClusterRoleBinding

　　5、元数据型资源

　　　　a、HPA

　　　　b、PodTemplate用于pod控制器创建pod时使用的模板。

　　　　c、LimitRange 定义资源限制

　　6、包括但不仅限于上述资源

三、yaml详解

　　1、将pod信息以yaml格式输出

[root@k8smaster ~]# kubectl get pods
NAME                          READY     STATUS    RESTARTS   AGE
myapp-848b5b879b-5k4s4        1/1       Running   0          22h
myapp-848b5b879b-bzblz        1/1       Running   0          22h
myapp-848b5b879b-hzbf5        1/1       Running   0          22h
nginx-deploy-5b595999-d9lv5   1/1       Running   0          1d
[root@k8smaster ~]# kubectl get pod myapp-848b5b879b-5k4s4 -o yaml  #以yaml格式输出
apiVersion: v1 #定义对象属于k8s哪一个对应的api群组的名称和版本，给定api版本时由两个部分组成，group/version，group如果省略，表示core定义（核心组，最根本的资源）
kind: Pod   #定义资源类别。用来指明这是每一种资源用来实例化成一个具体的资源对象时使用。
metadata:　　#元数据，内部嵌套很多二级字段和三级字段来定义
  creationTimestamp: 2019-05-09T09:10:00Z
  generateName: myapp-848b5b879b-
  labels:
    pod-template-hash: "4046164356"
    run: myapp
  name: myapp-848b5b879b-5k4s4
  namespace: default
  ownerReferences:
  - apiVersion: apps/v1
    blockOwnerDeletion: true
    controller: true
    kind: ReplicaSet
    name: myapp-848b5b879b
    uid: 8f3f5833-7232-11e9-be24-000c29d142be
  resourceVersion: "48605"
  selfLink: /api/v1/namespaces/default/pods/myapp-848b5b879b-5k4s4
  uid: 3977b5e7-723a-11e9-be24-000c29d142be
spec:  #specifications，规格。定义接下来需要创建的资源对象应该具有什么样的特性，应该满足什么样的规范。确保控制器能够被满足。
  containers:
  - image: ikubernetes/myapp:v1
    imagePullPolicy: IfNotPresent
    name: myapp
    resources: {}
    terminationMessagePath: /dev/termination-log
    terminationMessagePolicy: File
    volumeMounts:
    - mountPath: /var/run/secrets/kubernetes.io/serviceaccount
      name: default-token-jvtl7
      readOnly: true
  dnsPolicy: ClusterFirst
  nodeName: k8snode2
  priority: 0
  restartPolicy: Always
  schedulerName: default-scheduler
  securityContext: {}
  serviceAccount: default
  serviceAccountName: default
  terminationGracePeriodSeconds: 30
  tolerations:  #容忍度，能容忍哪些污点
  - effect: NoExecute
    key: node.kubernetes.io/not-ready
    operator: Exists
    tolerationSeconds: 300
  - effect: NoExecute
    key: node.kubernetes.io/unreachable
    operator: Exists
    tolerationSeconds: 300
  volumes:
  - name: default-token-jvtl7
    secret:
      defaultMode: 420
      secretName: default-token-jvtl7
status: #显示当前资源的当前的状态，只读，由系统维护，而spec由用户定义。如果当前状态和目标状态不一样，k8s就是为了确保每一个资源定义完以后其当前状态无限向目标状态靠近。从而能满足用户期望。
  conditions:
  - lastProbeTime: null
    lastTransitionTime: 2019-05-08T15:36:44Z
    status: "True"
    type: Initialized
  - lastProbeTime: null
    lastTransitionTime: 2019-05-08T15:36:46Z
    status: "True"
    type: Ready
  - lastProbeTime: null
    lastTransitionTime: null
    status: "True"
    type: ContainersReady
  - lastProbeTime: null
    lastTransitionTime: 2019-05-09T09:10:00Z
    status: "True"
    type: PodScheduled
  containerStatuses:
  - containerID: docker://0eccbcf513dc608277089bfe2a7b92e1639b1d63ec5d76212a65b30fffa78774
    image: ikubernetes/myapp:v1
    imageID: docker-pullable://ikubernetes/myapp@sha256:9c3dc30b5219788b2b8a4b065f548b922a34479577befb54b03330999d30d513
    lastState: {}
    name: myapp
    ready: true
    restartCount: 0
    state:
      running:
        startedAt: 2019-05-08T15:36:45Z
  hostIP: 192.168.10.12
  phase: Running
  podIP: 10.244.2.14
  qosClass: BestEffort
  startTime: 2019-05-08T15:36:44Z

　　2、创建资源的方法

　　　　a、apiserver在定义资源时仅接收json格式的资源定义，因此，像我们以前使用的run来创建deployment时，run命令会自动将给定的命令转成json格式。

　　　　b、yaml格式提供配置清单，apiserver可自动将其转为json，而后再提交；

　　3、大部分资源的配置清单都由五个组成：

　　　　a、apiVersion（group/version）：用来指明我们要创建的资源属于哪个资源群组　及版本，k8s把整个api-server所支持的api有多少种分组来进行管理。分了组后，某一组中的改变我们只需要改变一个组就行了，其它组不受影响可以继续使用，另外，还有一个功能，可以让一个组加版本号以后同一个群组不同版本还能够并存。pod是最核心资源，所以其属于核心群组 v1，控制器deployment等属于应用程序管理的核心资源，属于apps/v1。我们集群一般会有三个版本，阿尔法（内测版），贝塔（公测版），stable（稳定版）。

[root@k8smaster ~]# kubectl api-versions
admissionregistration.k8s.io/v1beta1
apiextensions.k8s.io/v1beta1
apiregistration.k8s.io/v1
apiregistration.k8s.io/v1beta1
apps/v1
apps/v1beta1
apps/v1beta2
authentication.k8s.io/v1
authentication.k8s.io/v1beta1
authorization.k8s.io/v1
authorization.k8s.io/v1beta1
autoscaling/v1
autoscaling/v2beta1
batch/v1
batch/v1beta1
certificates.k8s.io/v1beta1
events.k8s.io/v1beta1
extensions/v1beta1
networking.k8s.io/v1
policy/v1beta1
rbac.authorization.k8s.io/v1
rbac.authorization.k8s.io/v1beta1
scheduling.k8s.io/v1beta1
storage.k8s.io/v1
storage.k8s.io/v1beta1
v1

　　　　b、kind：资源类别

　　　　c、metadata：元数据，主要提供以下几个字段

　　　　　　1）、name，在同一类别中资源name是唯一的。实例化出来的这个资源类别下的实例的名称。

　　　　　　2）、namespace

　　　　　　3）、labels，每一种类型的资源都可以有标签，标签就是键值数据

　　　　　　4）、annotations，注释

　　　　　　5）、ownerReferences

　　　　　　6）、resourceVersion

　　　　　　7）、uid，唯一标识，由系统自动生成。

　　　　　　8）、selfLink，自引用，就是在我们api中这个资源的格式，比如

selfLink: /api/v1/namespaces/default/pods/myapp-848b5b879b-5k4s4 #在api下v1版本下namespaces为default中名称为

myapp-848b5b879b-5k4s4的pod资源类型
　　　　　　　　因此每个资源的引用PATH为固定格式 /api/GROUP/VERSION/namespaces/NAMESPACE/TYPE/NAME

　　　　　　　　...

　　　　d、spec：spec可能会嵌套很多其它的二级或三级字段，不同的资源类型其spec中可嵌套的字段不尽相同。其定义用户的期望状态（disired state），资源被创建后状态有可能会不符合条件，因此当前状态会向期望状态靠近。由于有很多字段，因此k8s有内建的格式定义可用explain查看。

[root@k8smaster ~]# kubectl explain（解释，注解） pod
KIND:     Pod
VERSION:  v1

DESCRIPTION:
     Pod is a collection of containers that can run on a host. This resource is
     created by clients and scheduled onto hosts.

FIELDS:
   apiVersion    <string>#字符串
     APIVersion defines the versioned schema of this representation of an
     object. Servers should convert recognized schemas to the latest internal
     value, and may reject unrecognized values. More info:
     https://git.k8s.io/community/contributors/devel/api-conventions.md#resources

   kind    <string>
     Kind is a string value representing the REST resource this object
     represents. Servers may infer this from the endpoint the client submits
     requests to. Cannot be updated. In CamelCase. More info:
     https://git.k8s.io/community/contributors/devel/api-conventions.md#types-kinds

   metadata    <Object>#对象，需要嵌套很多二级字段
     Standard object's metadata. More info:
     https://git.k8s.io/community/contributors/devel/api-conventions.md#metadata

   spec    <Object>
     Specification of the desired behavior of the pod. More info:
     https://git.k8s.io/community/contributors/devel/api-conventions.md#spec-and-status

   status    <Object>
     Most recently observed status of the pod. This data may not be up to date.
     Populated by the system. Read-only. More info:
     https://git.k8s.io/community/contributors/devel/api-conventions.md#spec-and-status

　　　　　　还可以做二级字段探究

[root@k8smaster ~]# kubectl explain pods.metadata
KIND:     Pod
VERSION:  v1

RESOURCE: metadata <Object>

DESCRIPTION:
     Standard object's metadata. More info:
     https://git.k8s.io/community/contributors/devel/api-conventions.md#metadata

     ObjectMeta is metadata that all persisted resources must have, which
     includes all objects users must create.

FIELDS:
   annotations    <map[string]string>
     Annotations is an unstructured key value map stored with a resource that
     may be set by external tools to store and retrieve arbitrary metadata. They
     are not queryable and should be preserved when modifying objects. More
     info: http://kubernetes.io/docs/user-guide/annotations

   clusterName    <string>
     The name of the cluster which the object belongs to. This is used to
     distinguish resources with same name and namespace in different clusters.
     This field is not set anywhere right now and apiserver is going to ignore
     it if set in create or update request.

...

　　　　e、status：当前状态（current state），本字段由kubernetes集群维护，用户不能定义它也不能删除它。

四、定义yaml文件

[root@k8smaster manifests]# pwd
/root/manifests
[root@k8smaster manifests]# ls
pod-demo.yaml
[root@k8smaster manifests]# cat pod-demo.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: pod-demo
  namespace: default
  labels: #也可以在此处写上{app:myapp,tier:frontend}代替下面两行
    app: myapp
    tier: frontend
spec:
  containers: #是一个列表，具体定义方式如下
  - name: myapp
    image: ikubernetes/myapp:v1
  - name: busybox
    image: busybox:latest
    command: #也可以写成中括号形式，比如可以在此处写上["/bin/sh","-c","sleep 3600"]
    - "/bin/sh"
    - "-c"
    - "echo ${date} >> /usr/share/nginx/html/index.html;sleep 5"
[root@k8smaster manifests]# kubectl create -f pod-demo.yaml 
Error from server (AlreadyExists): error when creating "pod-demo.yaml": pods "pod-demo" already exists
[root@k8smaster manifests]# kubectl get pods -o wide
NAME                          READY     STATUS             RESTARTS   AGE       IP            NODE
myapp-848b5b879b-5k4s4        1/1       Running            0          3d        10.244.2.14   k8snode2
myapp-848b5b879b-bzblz        1/1       Running            0          3d        10.244.1.21   k8snode1
myapp-848b5b879b-hzbf5        1/1       Running            0          3d        10.244.1.22   k8snode1
nginx-deploy-5b595999-d9lv5   1/1       Running            0          3d        10.244.2.4    k8snode2
pod-demo                      1/2       CrashLoopBackOff   7          17m       10.244.2.15   k8snode2
[root@k8smaster manifests]# kubectl describe pod pod-demo
Name:               pod-demo
Namespace:          default
Priority:           0
PriorityClassName:  <none>
Node:               k8snode2/192.168.10.12
Start Time:         Thu, 09 May 2019 12:26:59 +0800
Labels:             app=myapp
                    tier=frontend
Annotations:        kubectl.kubernetes.io/last-applied-configuration={"apiVersion":"v1","kind":"Pod","metadata":{"annotations":{},"labels":{"app":"myapp","tier":"frontend"},"name":"pod-demo
","namespace":"default"},"spec"...Status:             Running
IP:                 10.244.2.15
Containers:
  myapp:
    Container ID:   docker://b8e4c51d55ac57796b6f55499d119881ef522bcf43e673440bdf6bfe3cd81aa5
    Image:          ikubernetes/myapp:v1
    Image ID:       docker-pullable://ikubernetes/myapp@sha256:9c3dc30b5219788b2b8a4b065f548b922a34479577befb54b03330999d30d513
    Port:           <none>
    Host Port:      <none>
    State:          Running
      Started:      Thu, 09 May 2019 12:27:00 +0800
    Ready:          True
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-jvtl7 (ro)
  busybox:
    Container ID:  docker://1d3d2c9ab4768c1d9a9dda875c772e9a3a5a489408ad965b09af4d28ee5d5092
    Image:         busybox:latest
    Image ID:      docker-pullable://busybox@sha256:4b6ad3a68d34da29bf7c8ccb5d355ba8b4babcad1f99798204e7abb43e54ee3d
    Port:          <none>
    Host Port:     <none>
    Command:
      /bin/sh
      -c
      echo ${date} >> /usr/share/nginx/html/index.html;sleep 5
    State:          Waiting
      Reason:       CrashLoopBackOff
    Last State:     Terminated
      Reason:       Completed
      Exit Code:    0
      Started:      Thu, 09 May 2019 12:44:14 +0800
      Finished:     Thu, 09 May 2019 12:44:19 +0800
    Ready:          False
    Restart Count:  8
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-jvtl7 (ro)
Conditions:
  Type              Status
  Initialized       True 
  Ready             False 
  ContainersReady   False 
  PodScheduled      True 
Volumes:
  default-token-jvtl7:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-jvtl7
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type     Reason     Age               From               Message
  ----     ------     ----              ----               -------
  Normal   Pulled     4d                kubelet, k8snode2  Container image "ikubernetes/myapp:v1" already present on machine
  Normal   Created    4d                kubelet, k8snode2  Created container
  Normal   Started    4d                kubelet, k8snode2  Started container
  Normal   Pulling    4d (x4 over 4d)   kubelet, k8snode2  pulling image "busybox:latest"
  Normal   Pulled     4d (x4 over 4d)   kubelet, k8snode2  Successfully pulled image "busybox:latest"
  Normal   Created    4d (x4 over 4d)   kubelet, k8snode2  Created container
  Normal   Started    4d (x4 over 4d)   kubelet, k8snode2  Started container
  Warning  BackOff    4d (x63 over 4d)  kubelet, k8snode2  Back-off restarting failed container
  Normal   Scheduled  17m               default-scheduler  Successfully assigned default/pod-demo to k8snode2

　　　　　　查看日志

[root@k8smaster manifests]# curl 10.244.2.15
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
[root@k8smaster manifests]# kubectl logs pod-demo myapp
10.244.0.0 - - [09/May/2019:04:49:18 +0000] "GET / HTTP/1.1" 200 65 "-" "curl/7.29.0" "-"
[root@k8smaster manifests]# kubectl logs pod-demo busybox
/bin/sh: can't create /usr/share/nginx/html/index.html: nonexistent directory

　　　　　　改变容器busybox的启动命令后启动成功

[root@k8smaster manifests]# cat pod-demo.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: pod-demo
  namespace: default
  labels: #也可以在此处写上{app:myapp,tier:frontend}代替下面两行
    app: myapp
    tier: frontend
spec:
  containers: #是一个列表，具体定义方式如下
  - name: myapp
    image: ikubernetes/myapp:v1
  - name: busybox
    image: busybox:latest
    command: #也可以写成中括号形式，比如可以在此处写上["/bin/sh","-c","sleep 3600"]
    - "/bin/sh"
    - "-c"
    - "sleep 3600"
[root@k8smaster manifests]# kubectl get pods
NAME                          READY     STATUS    RESTARTS   AGE
myapp-848b5b879b-5k4s4        1/1       Running   0          3d
myapp-848b5b879b-bzblz        1/1       Running   0          3d
myapp-848b5b879b-hzbf5        1/1       Running   0          3d
nginx-deploy-5b595999-d9lv5   1/1       Running   0          3d
pod-demo                      2/2       Running   0          1m

　　　　　　进入到容器中

[root@k8smaster manifests]# kubectl exec -it pod-demo -c busybox /bin/sh
/ # ls
bin   dev   etc   home  proc  root  sys   tmp   usr   var
/ # 

 五、使用kubectl管理资源有三种用法

　　1、命令式用法

　　2、配置清单式用法 （命令式资源清单）

　　3、使用另外命令（声明式资源清单），确保资源尽可能的向我们声明的状态改变并随时应用。