Detailed explanation of kubernetes (XI) -- label and label selector

Today I will continue to introduce Linux Operation and maintenance related knowledge , The main content of this paper is Kubernetes Tags and tag selectors in .

One 、 Overview of labels and label selectors

（ One ） label

stay Kubernetes In the cluster , The tag itself is a key value pair type of data , And can be attached to any resource object , You can specify... When the resource object is created , Or add after the resource object is created . stay Kubernetes In the cluster , A resource object can have multiple tags , Multiple resource objects can also have the same label .
Kubernetes Tags in clusters have strict formats , Its Key The definition of can use letters 、 Numbers and underscores , Hyphens and periods , But it can only start with a character or a number .Value Can be null , You can also use letters 、 Numbers 、 Hyphens and dots , But you must use numbers or letters at the beginning and end .

（ Two ） tag chooser

stay Kubernetes In the cluster , The standard selection criteria for tags are .Kubernetes At present, two kinds of label selectors are supported , namely Based on equivalence and Based on set relation The label selector .
Label selector based on equivalence relation There are three kinds of ：
“==”、“=” and “!=”, The first two are equal to , The last expression is not equal to
Label selector based on set relation There are four kinds of ：
key in (VALUE1,VALUE2,VALUE3……), Indicates that the specified key value exists in the following collection .
key notin (VALUE1,VALUE2,VALUE3……), Indicates that the specified key value does not exist in the following collection .
key, A label indicating the existence of this key name .
!key, A label indicating that this key name does not exist .
The use of tag selectors follows the following logic ：
1、 When specifying multiple label selectors at the same time , The logical relationship of these multiple tag selectors is “ And ”.
2、 Using a null tag selector means selecting each resource object .
3、 An empty tag selector cannot select any resources .
Be careful , ad locum , An empty tag selector and a null tag selector have different meanings . An empty label selector means that there is no label selector , A null tag selector means that although there is a tag selector , However, the value of this tag selector is null .

Two 、 Label and label selector related commands

Next , Let me introduce the related commands of tags and tag selectors ：

（ One ） see Pod The label of the object

We're looking at Pod On the basis of objects , add –show-labels Parameters , You can see Pod The label of the object , for example , Carry out orders ：

kubectl get pods --show-labels

You can view the currently running Pod Its label , The execution result of this command is as follows ：

besides ,-L Parameters can show Pod The specified label of the object , Carry out orders ：

kubectl get pods -L 【 key A】

Can show all of Pod object , Pair containing keys A Labeled Pod Its value will be displayed , Yes, no keys A Labeled Pod Will display as empty .
for example , Carry out orders ：

kubectl get pods -L label1,label2

Can display the current Pod Object and its label1 and label2 label , The execution result of this command is as follows ：

（ Two ） The tag selector filters tags

stay kubectl In command ,-l Parameters can be used as filters for tags , for example , Carry out orders ：

kubectl get pods -l label1,label2

The filter can contain both lable1 and label2 Labeled Pod, The execution result of this command is as follows ：

（ 3、 ... and ）Pod Add labels after object creation

We can do it in Pod Object is labeled when it is created , We can also use label Command in Pod Add labels after object creation , The command format is as follows ：

kubectl label pods/【Pod name 】 【 Label key 】=【 Label value 】

for example , Carry out orders ：

kubectl label pods/pod-demo-test label3=label3

You can give pod-demo-test Of Pod Object to add label3=label3 The label of . The execution result of this command is as follows ：

（ Four ） modify Pod The label of the object

Except for the already running Pod In addition to adding labels to objects , We can also modify Pod The label of the object . This operation also requires the use of label command , And add... At the end –overwrite The order of . for example , Carry out orders ：

kubectl label pods/pod-demo-test label3=modify --overwrite

You can put the Pod The original label3=label3 It is amended as follows label3=modify, The execution result of this command is as follows ：

Originality is not easy. , Reprint please explain the source ：https://blog.csdn.net/weixin_40228200