标签
标签中的键名称通常由“键前缀”和“键名”组成，其格式形如“KEY_PREFIX/KEY_NAME”，键前缀为可选部分。键名至多能使用63个字符，支持字母、数字、连接号（-）、下划线（_）、点号（.）等字符，且只能以字母或数字开头。而键前缀必须为DNS子域名格式，且不能超过253个字符。省略键前缀时，键将被视为用户的私有数据。那些由Kubernetes系统组件或第三方组件自动为用户资源添加的键必须使用键前缀，kubernetes.io/和k8s.io/前缀预留给了kubernetes的核心组件使用，例如Node对象上常用的kubernetes.io/os、kubernetes.io/arch和kubernetes.io/hostname等。
标签的键值必须不能多于63个字符，它要么为空，要么是以字母或数字开头及结尾，且中间仅使用了字母、数字、连接号（-）、下划线（_）或点号（.）等字符的数据。
添加删除标签
命令行下添加删除标签
# Update pod 'foo' with the label 'unhealthy' and the value 'true'.
kubectl label pods foo unhealthy=true
# Update pod 'foo' with the label 'status' and the value 'unhealthy', overwriting any existing value.
kubectl label --overwrite pods foo status=unhealthy
# Update all pods in the namespace
kubectl label pods --all status=unhealthy
# Update a pod identified by the type and name in "pod.json"
kubectl label -f pod.json status=unhealthy
# Update pod 'foo' only if the resource is unchanged from version 1.
kubectl label pods foo status=unhealthy --resource-version=1
# Update pod 'foo' by removing a label named 'bar' if it exists.
# Does not require the --overwrite flag.
kubectl label pods foo bar-
应用打标规范
-
版本标签：” release” : “stable“，”release” : “canary“，”release” : “beta“。 -
环境标签：” environment” : “dev“，”environment” : “qa“，”environment” : “prod“。 -
应用标签：” app” : “ui“，”app” : “as“，”app” : “pc“，”app” : “sc“。 -
架构层级标签：” tier” : “frontend“，”tier” : “backend“, “tier” : “cache“。 -
分区标签：” partition” : “customerA“，”partition” : “customerB“。 -
品控级别标签：” track” : “daily“，”track” : “weekly“。
标签选择器
标签选择器用于表达标签的查询条件或选择标准，Kubernetes API目前支持两个选择器：基于等值关系（equality-based）的标签选项器以及基于集合关系（set-based）的标签选择器。同时指定多个选择器时需要以逗号将其分隔，各选择器之间遵循“与”逻辑，即必须要满足所有条件，而且空值的选择器将不选择任何对象。
基于等值关系的标签选择器的可用操作符有=、==和!=三种，其中前两个意义相同，都表示“等值”关系，最后一个表示“不等”。例如env=dev和env!=prod都是基于等值关系的选择器，而tier in (frontend,backend)则是基于集合关系的选择器。
创建标签时：release=alpha, 表示为资源进行打标。
标签选择器使用：release==alpha，表示过滤有release=alpha这个标签的资源，才符合条件。
-
KEY in (VALUE1,VALUE2,…)：指定的键名的值存在于给定的列表中即满足条件； -
KEY notin (VALUE1,VALUE2,…)：指定的键名的值不存在于给定列表中即满足条件； -
KEY：所有存在此键名标签的资源； -
!KEY：所有不存在此键名标签的资源。
标签选择器使用示例
当前集群中的pod
root@k8s-master01:~/yaml/chapter07# kubectl get pods --show-labels
NAME READY STATUS RESTARTS AGE LABELS
all-in-one 2/2 Running 0 20h <none>
demoapp-5f7d8f9847-jrfm6 1/1 Running 0 6d21h app=demoapp,pod-template-hash=5f7d8f9847
demoapp-5f7d8f9847-r7h7b 1/1 Running 0 6d18h app=demoapp,pod-template-hash=5f7d8f9847
demoapp-5f7d8f9847-v7ft8 1/1 Running 0 6d21h app=demoapp,pod-template-hash=5f7d8f9847
init-container-demo 1/1 Running 0 2d23h <none>
lifecycle-demo 1/1 Running 0 3d1h <none>
liveness-exec-demo 1/1 Running 2 3d19h <none>
liveness-httpget-demo 1/1 Running 1 3d6h <none>
liveness-tcpsocket-demo 1/1 Running 1410 3d7h <none>
memleak-pod 0/1 CrashLoopBackOff 563 47h app=memleak
mypod 1/1 Running 0 5d23h app=mypod,release=canary
mypod-host-network 1/1 Running 0 5d app=demoapp,release=canary
mypod-with-env-var 1/1 Running 0 5d1h app=mypod,release=canary
mypod-with-ports 1/1 Running 0 5d app=mypod,release=canary
readiness-httpget-demo 0/1 Running 0 3d2h <none>
securitycontext-capabilities-demo 1/1 Running 0 4d <none>
securitycontext-runasuser-demo 1/1 Running 0 4d1h <none>
securitycontext-sysctls-demo 1/1 Running 0 3d23h <none>
sidecar-container-demo 2/2 Running 0 2d23h <none>
stress-pod 1/1 Running 1 47h <none>
过滤出有app=demoapp的pod
root@k8s-master01:~/yaml/chapter07# kubectl get pods -l app=demoapp --show-labels
NAME READY STATUS RESTARTS AGE LABELS
demoapp-5f7d8f9847-jrfm6 1/1 Running 0 6d21h app=demoapp,pod-template-hash=5f7d8f9847
demoapp-5f7d8f9847-r7h7b 1/1 Running 0 6d19h app=demoapp,pod-template-hash=5f7d8f9847
demoapp-5f7d8f9847-v7ft8 1/1 Running 0 6d21h app=demoapp,pod-template-hash=5f7d8f9847
mypod-host-network 1/1 Running 0 5d app=demoapp,release=canary
也可以使用不等来过滤pod
root@k8s-master01:~/yaml/chapter07# kubectl get pods -l app!=demoapp --show-labels
NAME READY STATUS RESTARTS AGE LABELS
all-in-one 2/2 Running 0 21h <none>
init-container-demo 1/1 Running 0 3d <none>
lifecycle-demo 1/1 Running 0 3d1h <none>
liveness-exec-demo 1/1 Running 2 3d19h <none>
liveness-httpget-demo 1/1 Running 1 3d6h <none>
liveness-tcpsocket-demo 0/1 CrashLoopBackOff 1415 3d7h <none>
memleak-pod 0/1 CrashLoopBackOff 566 47h app=memleak
mypod 1/1 Running 0 5d23h app=mypod,release=canary
mypod-with-env-var 1/1 Running 0 5d1h app=mypod,release=canary
mypod-with-ports 1/1 Running 0 5d app=mypod,release=canary
readiness-httpget-demo 0/1 Running 0 3d2h <none>
securitycontext-capabilities-demo 1/1 Running 0 4d <none>
securitycontext-runasuser-demo 1/1 Running 0 4d1h <none>
securitycontext-sysctls-demo 1/1 Running 0 3d23h <none>
sidecar-container-demo 2/2 Running 0 2d23h <none>
stress-pod 1/1 Running 2 2d <none>
# 需要注意此处使用不等于时，没有LABEL的pod也会被选中。
选中所有没有app标签的pod
root@k8s-master01:~/yaml/chapter07# kubectl get pods -l '!app' --show-labels # 需要注意此处需要使用单引号，否则将作为shell命令执行。
NAME READY STATUS RESTARTS AGE LABELS
all-in-one 2/2 Running 0 21h <none>
init-container-demo 1/1 Running 0 3d <none>
lifecycle-demo 1/1 Running 0 3d1h <none>
liveness-exec-demo 1/1 Running 2 3d19h <none>
liveness-httpget-demo 1/1 Running 1 3d6h <none>
liveness-tcpsocket-demo 0/1 CrashLoopBackOff 1417 3d7h <none>
readiness-httpget-demo 0/1 Running 0 3d3h <none>
securitycontext-capabilities-demo 1/1 Running 0 4d <none>
securitycontext-runasuser-demo 1/1 Running 0 4d2h <none>
securitycontext-sysctls-demo 1/1 Running 0 3d23h <none>
sidecar-container-demo 2/2 Running 0 2d23h <none>
stress-pod 1/1 Running 2 2d <none>
对app键的值做判断
root@k8s-master01:~/yaml/chapter07# kubectl get pods -l 'app in (mypod,demoapp)' --show-labels
NAME READY STATUS RESTARTS AGE LABELS
demoapp-5f7d8f9847-jrfm6 1/1 Running 0 6d21h app=demoapp,pod-template-hash=5f7d8f9847
demoapp-5f7d8f9847-r7h7b 1/1 Running 0 6d19h app=demoapp,pod-template-hash=5f7d8f9847
demoapp-5f7d8f9847-v7ft8 1/1 Running 0 6d22h app=demoapp,pod-template-hash=5f7d8f9847
mypod 1/1 Running 0 5d23h app=mypod,release=canary
mypod-host-network 1/1 Running 0 5d app=demoapp,release=canary
mypod-with-env-var 1/1 Running 0 5d1h app=mypod,release=canary
mypod-with-ports 1/1 Running 0 5d1h app=mypod,release=canary
对app键做不存在判断
root@k8s-master01:~/yaml/chapter07# kubectl get pods -l 'app notin (mypod,demoapp)' --show-labels
NAME READY STATUS RESTARTS AGE LABELS
all-in-one 2/2 Running 0 21h <none>
init-container-demo 1/1 Running 0 3d <none>
lifecycle-demo 1/1 Running 0 3d1h <none>
liveness-exec-demo 1/1 Running 2 3d19h <none>
liveness-httpget-demo 1/1 Running 1 3d6h <none>
liveness-tcpsocket-demo 0/1 CrashLoopBackOff 1419 3d8h <none>
memleak-pod 0/1 CrashLoopBackOff 569 2d app=memleak
readiness-httpget-demo 0/1 Running 0 3d3h <none>
securitycontext-capabilities-demo 1/1 Running 0 4d <none>
securitycontext-runasuser-demo 1/1 Running 0 4d2h <none>
securitycontext-sysctls-demo 1/1 Running 0 3d23h <none>
sidecar-container-demo 2/2 Running 0 3d <none>
stress-pod 1/1 Running 2 2d <none>
# app键不存在和app的值非mypod或demoapp时都会被选中
对多个键值过滤
root@k8s-master01:~/yaml/chapter07# kubectl get pods -l 'app=demoapp,release=canary' --show-labels
NAME READY STATUS RESTARTS AGE LABELS
mypod-host-network 1/1 Running 0 5d app=demoapp,release=canary
# app和release之间为与逻辑必须要同时满足
原文始发于微信公众号（TechOps之窗）：轻松了解K8S标签选择器
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