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: 2019-05-08T15:36:44Z2、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
v1b、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。
来源：oschina
链接：https://my.oschina.net/u/4397179/blog/4405919