k8s Label 2

In k8s, we will easily deploy dozens or hundreds of microservices . The version of these microservices and the number of copies will bring out more pods

With so many pods, how can they be organized efficiently? If the organization is not good, the management microservices will become chaotic and disorganized

Therefore, there is a label Label

label

Tags are a simple but powerful feature of K8S that can organize resources in K8S, including pod resources

A label is an arbitrary key-value pair that can be attached to a resource to select a resource with that exact label

That is to say, the key of our label is arbitrary inside the resource and can be defined by yourself, as long as it is unique in the resource

for example

We can define 2 labels to organize the above messy multiple pods

Identify what application this pod belongs to

Identify the application version running in this pod, for example, the following version can be set

- stable
- beta
- canary

can be organized like this

By organizing microservices through the above labels, we can easily view the pod status we expect to see through the pod label

write a demo

Just use the previous xmt-kubia,yaml file and change it to xmt-kubia-labels.yaml

Plus 2 custom tags:

xmt_create: auto
rel: stable

apiVersion: v1
kind: Pod
metadata:
  name: xmt-kubia-labels
  labels:
    xmt_create: auto
    rel: stable
spec:
  containers:
  - image: xiaomotong888/xmtkubia
    name: xmtkubia-labels
    ports:
    - containerPort: 8080
      protocol: TCP

kubectl create -f xmt-kubia-labels.yamlRun the pod by

Check the actual label situation

view label

kubectl get pod --show-labels

view the specified label

kubectl get po -L rel,xmt_create

Modify the label of the pod

kubectl label pod xmt-kubia-labels key=value

Modify an existing label

kubectl label pod xmt-kubia-labels rel=dev --overwrite

label selector

Through the above case, I found that the label does not seem to be very useful. In fact, the label should be used in combination with the label selector

The label selector allows us to find out the corresponding pod set according to a specific label , and can operate on these pod sets

A tag selector is a criterion used to filter resources that contain a specific tag with a specific value, as follows:

Include or not include tags with specific keys
Contains tags with specific key-values
Contains tags with a specific key value, but the corresponding value is different from what we specified

Use tag selector

list pods

kubectl get po -l key=value

kubectl get po -l rel=dev

List pods containing a label

kubectl get po -l rel

To list pods that do not contain a certain label , you need to use single quotes to wrap the condition

kubectl get po -l '!rel'

Using an exclamation mark , this condition can be written !relto indicate that the rel tag is not included, because the bash shell will parse the exclamation mark, so we use !, and single quotes '' can be used for inclusion and processing

It can also be added after -lkey=value

or key != value,

use in ,kubectl get po -l 'rel in (dev,prod)'

use notin ,kubectl get po -l 'rel notin (dev,prod)'

Using multiple conditions in label selector

kubectl get pod -l 条件1,条件2...

The label selector can help us list the filtered pods, and we can also perform a certain type of operation on all pods in a subset, such as deleting all pods in a subset, which can be written like thiskubectl delete pod -l xx=xx

Labels can be used to categorize worker nodes

When we create pods, there will be such requirements. Some pods we create have higher requirements for CPU computing performance, so I need to deploy such pods to nodes with good performance. In this case, the program is actually Strongly coupled with the infrastructure

But the idea of K8S is not equivalent. The idea in K8S is that the application hides the actual infrastructure . In K8S, the created pods are randomly assigned to different nodes.

Then, we need to achieve the above requirements, we can do it through the label

Label the node

We said earlier that labels can not only be added to pods, but can actually be added to all resources in K8S

For example, we can add a label to our node, such as: gpu=true, it is better to specify the gpu of this node, and temporarily use minikube to demonstrate

Schedule the pod to the specified node

Continuing the above demo, create a new xmt-kubia-gpu.yaml file, add a node selector under Spec, nodeSlector , specify to select the node with gpu: "true"

Use kubectl create -f xmt-kubia-gpu.yamlto place the created pod on the node with the label gpu: "true" for scheduling

We should schedule pods considering groups of logical nodes matching certain criteria via label selectors

By the way:

If we really want to specify that the pod is scheduled to a specified node, we can also do it. We can check kubectl get node --show-labelsthe label of the node

We can see that there is a label whose key is kubernetes.io/hostname , and the corresponding value is the hostname of the node, so we can use this label to schedule our pod to the specified node

This approach has a risk. If the node we specify is offline, the pod we created will not be schedulable. This method is technically feasible, but it is not recommended

annotation

annotations

Annotations are similar to labels, but unlike labels, annotations cannot be used to group objects like labels

Annotations can accommodate more information and help us understand the role of resources more smoothly. Annotations are also in the form of key-value pairs

Add and modify annotations

kubectl annotate pod podName 具体的键值对

Namespaces

Namespace namespace

Different namespaces can have the same resource name

View namespace

kubectl get ns

View the pods in the specified namespace

kubectl get pod --namespace xxx

create a namespace

How to use commands

kubectl create namespace xxx

The way to use yaml

Write a yaml file and use kubectl create to create it

apiVersion: v1
kind: Namespace
metadata:
  name: test_ns

delete namespace

kubectl delete ns xxx

Delete the pod of the namespace, but keep the namespace

kubectl delete pod --all

If there is an RC in the namespace, the deleted pod will be recreated, and the RC will detect the number of copies of the pod. If it is less than the set number of copies, it will be created dynamically

Delete all resources in the namespace

kubectl delete all --all

That’s all for today, what I have learned, if there is any deviation, please correct me

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