K8S基础 - 03Pod入门

Posted on 2021-11-22 21:25 Kingdomer 阅读(197) 评论(0) 编辑收藏举报

K8S基础 - 03Pod入门

一、 Pod概念

1.1 每个Pod内都有一个根容器： pause容器

1.2 Pod存在的意义

创建容器使用docker, 一个docker容器对于一个应用程序，一个容器一个进程
Pod是多进程设计的，运行多个应用程序
为了亲密性的应用：两个应用之间进行交互; 网络之间调用; 两个应用需要频繁调用

1.3 Pod 内部共享

容器之间默认是相互隔离的，依赖于 Namespace 和 CGroup 机制
共享网络：通过Pause容器, 把其他业务容器加入到Pause容器里，让所有业务容器在同一命名空间中，实现网络共享
共享存储：引入数据卷概念Volume，使用数据卷进行持久化存储

二、命令创建Pod

2.1 kubectl run 创建Pod

[root@k8s-node31 ~]# kubectl run nginx-deploy --image=nginx:1.20.0-alpine --port=80 --replicas=1 --dry-run=true
Flag --replicas has been deprecated, has no effect and will be removed in the future.
W1005 10:17:03.359048  112699 helpers.go:567] --dry-run=true is deprecated (boolean value) and can be replaced with --dry-run=client.
pod/nginx-deploy created (dry run)

[root@k8s-node31 ~]# kubectl run nginx-deploy --image=nginx:1.20.0-alpine --port=80 --dry-run=client
pod/nginx-deploy created (dry run)

[root@k8s-node31 ~]# kubectl run nginx-deploy --image=nginx:1.20.0-alpine --port=80
pod/nginx-deploy created
[root@k8s-node31 ~]# kubectl get deployment
NAME             READY   UP-TO-DATE   AVAILABLE   AGE
nginx-deploy      1      1            1           2d1h

2.2 kubectl expose 暴露端口

kubectl expose (-f FILENAME | TYPE NAME) [--port=port] [--protocol=TCP|UDP|SCTP] [--target-port=number-or-name]
[--name=name] [--external-ip=external-ip-of-service] [--type=type] [options]

[root@k8s-node31 ~]# kubectl expose pod nginx-deploy --name=nginx-svc --port=80 --target-port=80 --protocol=TCP
service/nginx-svc exposed
[root@k8s-node31 ~]# kubectl get svc
NAME         TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)   AGE
kubernetes   ClusterIP   10.96.0.1        <none>        443/TCP   115d
nginx-svc    ClusterIP   10.108.204.249   <none>        80/TCP    8s

[root@k8s-node31 ~]# curl 10.108.204.249

[root@k8s-node31 ~]# kubectl get svc -n kube-system
NAME       TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)                  AGE
kube-dns   ClusterIP   10.96.0.10   <none>        53/UDP,53/TCP,9153/TCP   19d
[root@k8s-node31 ~]# kubectl get pods -n kube-system
NAME                                            READY   STATUS    RESTARTS   AGE
coredns-f9fd979d6-679dg                         1/1     Running   4          19d
coredns-f9fd979d6-j74z9                         1/1     Running   5          19d

[root@k8s-node31 ~]# kubectl exec -it nginx-deploy -- /bin/sh
/ # cat /etc/resolv.conf 
nameserver 10.96.0.10
search default.svc.cluster.local svc.cluster.local cluster.local bearpx.com
options ndots:5

[root@k8s-master ~]# kubectl get svc
NAME                   TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)        AGE
kubernetes             ClusterIP   10.96.0.1        <none>        443/TCP        19d
svc-nginx              NodePort    10.107.97.86     <none>        80:30088/TCP   2d23h

2.3 测试服务访问：宿主机、Pod

[root@k8s-master ~]# yum install bind-utils

[root@k8s-master ~]# dig -t A svc-nginx.default.svc.cluster.local @10.96.0.10

; <<>> DiG 9.11.26-RedHat-9.11.26-4.el8_4 <<>> -t A svc-nginx.default.svc.cluster.local @10.96.0.10
;; global options: +cmd
;; Got answer:
;; WARNING: .local is reserved for Multicast DNS
;; You are currently testing what happens when an mDNS query is leaked to DNS
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 45483
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 3db51b9f60c4708e (echoed)
;; QUESTION SECTION:
;svc-nginx.default.svc.cluster.local. IN	A

;; ANSWER SECTION:
svc-nginx.default.svc.cluster.local. 30	IN A	10.107.97.86

;; Query time: 2 msec
;; SERVER: 10.96.0.10#53(10.96.0.10)
;; WHEN: 六 10月 23 10:27:16 CST 2021
;; MSG SIZE  rcvd: 127

[root@k8s-master ~]# kubectl run client --image=busybox --replicas=1 -it --restart=Never
/ #  wget -O - -q http://svc-nginx:80/
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
html { color-scheme: light dark; }
body { width: 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

三、YAML文件创建Pod

3.1 命令创建的局限

# 使用kubectl run 只能创建一个Pod
[root@k8s-master ~]# kubectl run mynginx --image=sun2010wg/my-nginx:v1 --replicas=3 
Flag --replicas has been deprecated, has no effect and will be removed in the future.
pod/mynginx created
[root@k8s-master ~]# kubectl get pods
NAME                        READY   STATUS    RESTARTS   AGE
mynginx                     1/1     Running   0          12s

[root@k8s-master ~]# kubectl delete pod mynginx
pod "mynginx" deleted

# 获取yaml文件
[root@k8s-master ~]# kubectl create deployment web --image=nginx -o yaml --dry-run=client > my1.yml
[root@k8s-master ~]# kubectl get deployment nginx -o=yaml  > my2.yml

3.2 自主式Pod资源

资源的清单格式：

apiVersion(group/version), kind, metadata(name, namespace, labels,annotations,...)，spec, status(只读)

[root@k8s-master ~]# kubectl explain pod
KIND:     Pod
VERSION:  v1
FIELDS:
   apiVersion	<string>
   kind	        <string>
   metadata     <Object>
   spec	        <Object>
   status       <Object>

镜像拉取策略IfNotPresent

IfNotPresent: 默认值, 镜像在宿主机上不存在时才会拉取
Always：每次创建Pod都会重新拉取镜像
Never： Pod永远不会主动拉取镜像

[root@k8s-master pod-k8s]# cat pod-demo.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: pod-demo
  namespace: default
  labels:
    app: demo
    tier: frontend
spec:
  containers:
  - name: mynginx
    image: sun2010wg/my-nginx:v1
    imagePullPolicy: IfNotPresent    ### Always, Never, IfNotPresent
  restartPolicy: Always

容器重启策略restartPolicy：

Always：当容器终止退出后，总是重启容器, 默认策略
OnFailure：当容器异常退出(退出状态码非0)时，才会重启容器
Never：当容器终止退出，不会重启容器

使用command和args 修改镜像中的默认应用

[root@k8s-master pod-k8s]# cat pod-demo.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: pod-demo
  namespace: default
  labels:
    app: demo
    tier: frontend
spec:
  containers:
  - name: mynginx
    image: sun2010wg/my-nginx:v1
  - name: busybox
    image: busybox
#    command: ["/bin/sh", "-c" "sleep 3600"]
    command:
    - "/bin/sh"
    - "-c"
    - "sleep 3600"

3.3 Pod控制器

[root@k8s-master pod-k8s]# cat dep-mynginx.yaml 
apiVersion: apps/v1
kind: Deployment
metadata:
  name: mynginx-app
spec:
  replicas: 2
  selector:
    matchLabels:
      app: mynginx
  template:
    metadata:
      labels:
        app: mynginx
    spec:
      containers:
      - name: mynginx
        image: sun2010wg/my-nginx:v1
        imagePullPolicy: Never
        ports:
        - containerPort: 80

[root@k8s-master ~]# kubectl get deploy 
NAME          READY   UP-TO-DATE   AVAILABLE   AGE
mynginx-app   2/2     2            2           10m

[root@k8s-master pod-k8s]# kubectl get pods --show-labels
NAME                              READY   STATUS    RESTARTS   AGE     LABELS
mynginx-app-bddc44777-fx6gj       1/1     Running   1          2d10h   app=mynginx,pod-template-hash=bddc44777
mynginx-app-bddc44777-p9lkh       1/1     Running   1          2d10h   app=mynginx,pod-template-hash=bddc44777

3.4 使用Service暴露端口

[root@k8s-master pod-k8s]# cat svc-mynginx.yaml 
apiVersion: v1
kind: Service
metadata:
  name: svc-mynginx
spec:
  type: NodePort
  selector:
    app: mynginx
  ports:
  - name: http
    nodePort: 30089
    port: 80
    targetPort: 80

[root@k8s-master ~]# kubectl apply -f svc-mynginx.yaml 
service/svc-mynginx created
[root@k8s-master ~]# kubectl get svc
NAME          TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)        AGE
kubernetes    ClusterIP   10.96.0.1        <none>        443/TCP        16d
svc-mynginx   NodePort    10.109.228.159   <none>        80:30089/TCP   10s

使用Service IP地址访问

/ # wget -O - -q 10.109.228.159/hostname.html
mynginx-app-cbc4dcd5d-79lvd
/ # wget -O - -q 10.109.228.159/hostname.html
mynginx-app-cbc4dcd5d-9dbb5
/ # wget -O - -q 10.109.228.159/hostname.html
mynginx-app-cbc4dcd5d-79lvd
/ # wget -O - -q 10.109.228.159/hostname.html
mynginx-app-cbc4dcd5d-79lvd
/ # wget -O - -q 10.109.228.159/hostname.html
mynginx-app-cbc4dcd5d-79lvd
/ # wget -O - -q 10.109.228.159/hostname.html
mynginx-app-cbc4dcd5d-9dbb5

使用Service 名称访问

/ # wget -O - -q svc-mynginx/hostname.html
mynginx-app-cbc4dcd5d-79lvd
/ # 
/ # wget -O - -q svc-mynginx/hostname.html
mynginx-app-cbc4dcd5d-9dbb5

/ # while true; do wget -O - -q svc-mynginx/hostname.html; sleep 1; done
mynginx-app-cbc4dcd5d-79lvd
mynginx-app-cbc4dcd5d-9dbb5
mynginx-app-cbc4dcd5d-9dbb5
mynginx-app-cbc4dcd5d-79lvd
mynginx-app-cbc4dcd5d-9dbb5
mynginx-app-cbc4dcd5d-9dbb5
mynginx-app-cbc4dcd5d-9dbb5

[root@k8s-master pod-k8s]# kubectl edit svc svc-mynginx
Edit cancelled, no changes made.

四、Pod管理

4.1 扩展Pod数量

[root@k8s-master ~]# kubectl scale --replicas=3 deployment mynginx-app
deployment.apps/mynginx-app scaled
[root@k8s-master ~]# kubectl get deploy
NAME          READY   UP-TO-DATE   AVAILABLE   AGE
mynginx-app   3/3     3            3           17m

[root@k8s-master ~]# kubectl get pods
NAME                          READY   STATUS    RESTARTS   AGE
mynginx-app-cbc4dcd5d-79lvd   1/1     Running   0          17m
mynginx-app-cbc4dcd5d-9dbb5   1/1     Running   0          17m
mynginx-app-cbc4dcd5d-l6flg   1/1     Running   0          25s

/ # while true; do wget -O - -q svc-mynginx/hostname.html; sleep 1; done
mynginx-app-cbc4dcd5d-l6flg
mynginx-app-cbc4dcd5d-79lvd
mynginx-app-cbc4dcd5d-9dbb5
mynginx-app-cbc4dcd5d-l6flg

4.2 更新容器的镜像

[root@k8s-master ~]# kubectl set image deployment mynginx-app mynginx=sun2010wg/my-nginx:v2
deployment.apps/mynginx-app image updated
[root@k8s-master ~]# kubectl edit deploy mynginx-app
Edit cancelled, no changes made.

[root@k8s-master ~]# kubectl set image deployment mynginx-app mynginx=sun2010wg/my-nginx:v1
deployment.apps/mynginx-app image updated

### 查看滚动更新进度
[root@k8s-master ~]# kubectl rollout status deployment mynginx-app
Waiting for deployment "mynginx-app" rollout to finish: 2 out of 3 new replicas have been updated...
Waiting for deployment "mynginx-app" rollout to finish: 2 out of 3 new replicas have been updated...
Waiting for deployment "mynginx-app" rollout to finish: 2 old replicas are pending termination...
Waiting for deployment "mynginx-app" rollout to finish: 1 old replicas are pending termination...
Waiting for deployment "mynginx-app" rollout to finish: 1 old replicas are pending termination...
deployment "mynginx-app" successfully rolled out

每次更新都是生成新的Pod

/ # while true; do wget -O - -q svc-mynginx/hostname.html; sleep 1; done
mynginx-app-bddc44777-jvcrt
mynginx-app-bddc44777-c2msr
mynginx-app-bddc44777-lzgjr

### 回滚到上一次配置
[root@k8s-master ~]# kubectl rollout undo deployment mynginx-app
deployment.apps/mynginx-app rolled back

/ # while true; do wget -O - -q svc-mynginx/hostname.html; sleep 1; done
mynginx-app-cbc4dcd5d-b276w
mynginx-app-cbc4dcd5d-r8q8p
mynginx-app-cbc4dcd5d-f8cwz

4.3 更新Service配置

可以访问集群中的任意节点IP:30088

apiVersion: v1
kind: Service
metadata:
  name: svc-nginx
spec:
  type: NodePort
  selector:
    app: nginx
  ports:
  - name: http
    nodePort: 30088
    port: 80
    targetPort: 80

[root@k8s-master pod-k8s]# kubectl get svc
NAME                   TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)        AGE
svc-nginx              NodePort    10.107.97.86     <none>        80:30088/TCP   2d23h

4.4 Pod中多个容器

[root@k8s-master pod-k8s]# cat pod-demo.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: pod-demo               ### Pod名称
  namespace: default
  labels:
    app: demo
    tier: frontend
spec:
  containers:
  - name: mynginx              ### 容器名称
    image: sun2010wg/my-nginx:v1
  - name: busybox
    image: busybox
#    command: ["/bin/sh", "-c" "sleep 3600"]
    command:
    - "/bin/sh"
    - "-c"
    - "sleep 3600"

[root@k8s-master ~]# curl 10.244.3.10/hostname.html
pod-demo
[root@k8s-master ~]# kubectl logs pod-demo mynginx
/docker-entrypoint.sh: /docker-entrypoint.d/ is not empty, will attempt to perform configuration
/docker-entrypoint.sh: Looking for shell scripts in /docker-entrypoint.d/
/docker-entrypoint.sh: Launching /docker-entrypoint.d/10-listen-on-ipv6-by-default.sh
10-listen-on-ipv6-by-default.sh: info: IPv6 listen already enabled
/docker-entrypoint.sh: Launching /docker-entrypoint.d/20-envsubst-on-templates.sh
/docker-entrypoint.sh: Launching /docker-entrypoint.d/30-tune-worker-processes.sh
/docker-entrypoint.sh: Configuration complete; ready for start up
2021/10/23 06:36:31 [notice] 1#1: using the "epoll" event method
2021/10/23 06:36:31 [notice] 1#1: nginx/1.20.0
2021/10/23 06:36:31 [notice] 1#1: built by gcc 10.2.1 20201203 (Alpine 10.2.1_pre1) 
2021/10/23 06:36:31 [notice] 1#1: OS: Linux 4.18.0-193.28.1.el8_2.x86_64
2021/10/23 06:36:31 [notice] 1#1: getrlimit(RLIMIT_NOFILE): 1048576:1048576
2021/10/23 06:36:31 [notice] 1#1: start worker processes
2021/10/23 06:36:31 [notice] 1#1: start worker process 23
2021/10/23 06:36:31 [notice] 1#1: start worker process 24
10.244.0.0 - - [23/Oct/2021:06:37:10 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.61.1" "-"
10.244.0.0 - - [23/Oct/2021:06:37:16 +0000] "GET /hostname.html HTTP/1.1" 200 9 "-" "curl/7.61.1" "-"

Pod内的多个容器共享网络，文件系统独立

[root@k8s-master ~]# kubectl exec -it pod-demo -c mynginx -- /bin/sh
/ # ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
3: eth0@if14: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1450 qdisc noqueue state UP 
    link/ether ae:22:0d:cd:c1:b7 brd ff:ff:ff:ff:ff:ff
    inet 10.244.3.10/24 brd 10.244.3.255 scope global eth0
       valid_lft forever preferred_lft forever
/ # ls
bin                   docker-entrypoint.sh  lib                   opt                   run                   sys                   var
dev                   etc                   media                 proc                  sbin                  tmp
docker-entrypoint.d   home                  mnt                   root                  srv                   usr
/ # exit

[root@k8s-master ~]# kubectl exec -it pod-demo -c busybox -- /bin/sh
/ # ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
3: eth0@if14: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1450 qdisc noqueue 
    link/ether ae:22:0d:cd:c1:b7 brd ff:ff:ff:ff:ff:ff
    inet 10.244.3.10/24 brd 10.244.3.255 scope global eth0
       valid_lft forever preferred_lft forever
/ # 
~ # cd /
/ # ls
bin   dev   etc   home  proc  root  sys   tmp   usr   var
/ # mkdir /data
/ # exit

4.5 删除Pod

[root@k8s-master ~]# kubectl delete -f pod-demo.yaml 
pod "pod-demo" deleted

[root@k8s-master ~]# kubectl get pods
NAME                          READY   STATUS        RESTARTS   AGE
pod-demo                      2/2     Terminating   0          4m30s

五、标签

key=value

key: 字母、数字、_(下划线)、-(中划线)
value：可以为空，只能以字母或数字开头及结尾，中间可使用

5.1 查看标签，筛选Pod

[root@k8s-master ~]# kubectl get pods --show-labels
NAME                          READY   STATUS    RESTARTS   AGE     LABELS
client                        1/1     Running   0          4h38m   run=client        # 默认标记
mynginx-app-bddc44777-fx6gj   1/1     Running   0          3h28m   app=mynginx,pod-template-hash=bddc44777
mynginx2                      1/1     Running   0          3h38m   run=mynginx2
nginx-app-c6744f88d-bc6k2     1/1     Running   1          16h     app=nginx,pod-template-hash=c6744f88d

[root@k8s-master ~]# kubectl get pods -L app       # 显示app的值
NAME                          READY   STATUS    RESTARTS   AGE     APP
client                        1/1     Running   0          4h38m   
mynginx-app-bddc44777-fx6gj   1/1     Running   0          3h29m   mynginx
mynginx2                      1/1     Running   0          3h39m   
nginx-app-c6744f88d-bc6k2     1/1     Running   1          16h     nginx
# 标签中有key为app的Pod
[root@k8s-master ~]# kubectl get pods -l app
NAME                          READY   STATUS    RESTARTS   AGE
mynginx-app-bddc44777-fx6gj   1/1     Running   0          3h29m
nginx-app-c6744f88d-bc6k2     1/1     Running   1          16h

[root@k8s-master ~]# kubectl get pods -l app --show-labels
NAME                          READY   STATUS    RESTARTS   AGE     LABELS
mynginx-app-bddc44777-fx6gj   1/1     Running   0          3h30m   app=mynginx,pod-template-hash=bddc44777
nginx-app-c6744f88d-bc6k2     1/1     Running   1          16h     app=nginx,pod-template-hash=c6744f88d

5.2 给Pod添加Label

[root@k8s-master ~]# kubectl label pods pod-demo release=canary
pod/pod-demo labeled
[root@k8s-master ~]# kubectl label pods pod-demo release=stable --overwrite
pod/pod-demo labeled

[root@k8s-master ~]# kubectl get pods --show-labels
NAME                          READY   STATUS    RESTARTS   AGE     LABELS
pod-demo                      2/2     Running   0          85s     app=demo,release=stable,tier=frontend

5.3 查询符合多个标签的Pod

[root@k8s-master ~]# kubectl get pods -L app,run
NAME                          READY   STATUS    RESTARTS   AGE     APP       RUN
client                        1/1     Running   0          4h40m             client
mynginx-app-bddc44777-fx6gj   1/1     Running   0          3h30m   mynginx   
mynginx2                      1/1     Running   0          3h40m             mynginx2
nginx-app-c6744f88d-bc6k2     1/1     Running   1          16h     nginx     

[root@k8s-master ~]# kubectl get pods -l release, app       # 不能带空格
error: name cannot be provided when a selector is specified
[root@k8s-master ~]# kubectl get pods -l release,app 
NAME       READY   STATUS    RESTARTS   AGE
pod-demo   2/2     Running   0          4m19s

5.4 标签选择器

等值关系： =, ==, !=
集合关系：
- KEY in (value1, value2,...) KEY notin (value1, value2,...)
- KEY !KEY
许多资源支持内嵌字段定义其使用的标签选择器： matchLabels
- matchExpressions: 基于给定的表达式来定义使用标签选择器。 {key:"KEY", operator:"OPERATOR"，values:[VAL1,VAL2,...]}
- 操作符： In, NotIn: Values字段的值必须为非空列表； Exists, NotExists: values字段的值必须为非空列表

[root@k8s-master ~]# kubectl get pods -l release=stable,app=mynginx
No resources found in default namespace.
[root@k8s-master ~]# kubectl get pods -l release=stable,app=demo
NAME       READY   STATUS    RESTARTS   AGE
pod-demo   2/2     Running   0          4m43s

[root@k8s-master ~]# kubectl get pods -l "release in (stable, beta)"

[root@k8s-master ~]# kubectl get pods -l "release notin (alpha, beta)"

5.5 节点选择标签

[root@k8s-master ~]# kubectl label nodes k8s-node33.bearpx.com disktype=ssd
node/k8s-node33.bearpx.com labeled

[root@k8s-master pod-k8s]# cat pod-ssd.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: pod-ssd
  namespace: default
  labels:
    app: ssd
  annotations:
    kunking.com/created-by: cluster admin
spec:
  containers:
  - name: mynginx
    image: sun2010wg/my-nginx:v1
    ports:
    - name: http
      containerPort: 80
    - name: https
      containerPort: 443
  nodeSelector:
    disktype: ssd

[root@k8s-master ~]# kubectl apply -f pod-ssd.yaml 
pod/pod-ssd created

[root@k8s-master ~]# kubectl get pods -o wide
NAME       READY   STATUS    RESTARTS   AGE     IP            NODE                    NOMINATED NODE   READINESS GATES
pod-ssd    1/1     Running   0          24s     10.244.2.13   k8s-node33.bearpx.com   <none>           <none>

5.6 annotations

与labels不同的地方在于，它不能用于挑选资源对象，仅用于为对象提供"元数据"。

[root@k8s-master ~]# kubectl describe pod pod-ssd
Name:         pod-ssd
Namespace:    default
Priority:     0
Node:         k8s-node33.bearpx.com/192.168.6.33
Start Time:   Sat, 23 Oct 2021 15:28:20 +0800
Labels:       app=ssd
Annotations:  kunking.com/created-by: cluster admin
Status:       Running
IP:           10.244.2.15

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