Kubernetes resource list: how to create resources?

stay Kubernetes The content of all operations in , We all call it “ Resource objects ”, By API Server be based on HTTP/HTTPS Receive and respond to the client's operation request , It's a kind of Restful Style interface , Abstract all kinds of components and operation contents into standard REST resources , Such as Namespace、Pod etc. , The operation contents are as follows JSON or yml Format data for operation .

This article is about Kubernetes The most important section in —— Resource list  , We want to Kubernetes Deployment in China Pod、Service Equal resource object , All of them need to be deployed by means of resource list , Whether by command kubectl , Or the visual console , The definition of resource list is indispensable , This article focuses on how to define a resource list 、 How to create and use .

1、 Resource classification

Classify resources according to their functions ,Kubernetes Resource objects can be divided into ：

• The workload （Workload）：Pod、ReplicaSet、Deployment、StatefulSet、DaemonSet、Job、CronJob.
• Discovery and load balancing （Discovery & LB）：Service 、Ingress.
• Configuration and storage （Config & Storage）： Volume（ Storage volume ）、CSI（ Container storage interface , Can expand a variety of third-party storage volumes ）.
• colony （Cluster） ：Namespace、Node、Role、ClusterRole、RoleBinding（ Character binding ）、ClusterRoleBinding（ Cluster role binding ）.
• Metadata （Metadata） ：HPA、PodTemplate（Pod Templates , Used to let the controller create Pod The template used when ）、LimitRange（ Used to define hardware resource constraints ）.

An application usually needs the support of multiple resources , for example , Use Deployment Examples of resource management applications （Pod）、 Use ConfigMap Resource saving application configuration 、 Use Service or Ingress Resource exposure Services 、 Use Volume Resources provide external storage, etc .

2. Resource list

Resource list , It's equivalent to a play , Can tell us how to do each step ,Kubernetes Received such a script , It can be executed according to this script , To meet our expectations .

stay Kubernetes in , Generally, resources are created by defining resource lists . In general use yaml File format to create resources that meet our expectations , In this way yaml We call the document ** Resource list ** .（ It can also be defined as json Format ）

Such as , Create a Pod resources ：

apiVersion: v1kind: Podmetadata:  name: vue-frontend  namespace: test  labels:    app: vue-frontendspec:  containers:  - name: vue-frontend    image: xcbeyond/vue-frontend:latest    ports:      - name: port        containerPort: 80        hostPort: 8080

Next , With Pod Resource definition as an example to expand the detailed description of the resource list .

2.1 Resource list definition

yaml Format Pod The complete contents of the resource list definition file are as follows ：

apiVersion: v1kind: Pod  #  Resource categories metadata:  #  Resource metadata   name: string  namespace: string  labels:    - name: string  annotations:    - name: stringspec:   #  The state of resource expectations   containers:  #  List of containers     - name: string  #  Container name , The following attributes belong to the definition or constraint of the container       image: string        imagePullPolicy: [Always|Never|IfNotPresent]      command: [string]      args: [string]      workingDir: string      volumeMounts:        - name: string          mountPath: string          readOnly: boolean      ports:        - name: string          containerPort: int          hostPort: int          protocol: string      env:        - name: string          value: string      resources:        limits:          cpu: string          memory: string        requests:          cpu: string          memory: string      livenssProbe:        exec:          command: [string]        httpGet:          path: string          port: number          host: string          scheme: string          httpHeaders:            - name: string              value: string          tcpSocket:            port: number          initialDelaySeconds: 0          timeoutSeconds: 0          periodSeconds: 0          successThreshold: 0          failureThreshold: 0……

A detailed description of each attribute is shown in the following table ：

（ Required attributes , Must exist , Otherwise, the creation fails .）

The above list of common properties , If you want to see all properties , You can use commands `kubectl explain pod`：

[[email protected] ~]$ kubectl explain podKIND:     PodVERSION:  v1DESCRIPTION:     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>     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/sig-architecture/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/sig-architecture/api-conventions.md#types-kinds   metadata <Object>     Standard object's metadata. More info:    https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata   spec <Object>     Specification of the desired behavior of the pod. More info:    https://git.k8s.io/community/contributors/devel/sig-architecture/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/sig-architecture/api-conventions.md#spec-and-status

See the property description , Use the following command , Such as ： see pod.spec.containers

[[email protected] ~]$ kubectl explain pod.spec.containersKIND:     PodVERSION:  v1RESOURCE: containers <[]Object>DESCRIPTION:     List of containers belonging to the pod. Containers cannot currently be     added or removed. There must be at least one container in a Pod. Cannot be     updated.     A single application container that you want to run within a pod.FIELDS:   args <[]string>     Arguments to the entrypoint. The docker image's CMD is used if this is not     provided. Variable references $(VAR_NAME) are expanded using the     container's environment. If a variable cannot be resolved, the reference in     the input string will be unchanged. The $(VAR_NAME) syntax can be escaped     with a double $$, ie: $$(VAR_NAME). Escaped references will never be     expanded, regardless of whether the variable exists or not. Cannot be     updated. More info:    https://kubernetes.io/docs/tasks/inject-data-application/define-command-argument-container/#running-a-command-in-a-shell   command  <[]string>     Entrypoint array. Not executed within a shell. The docker image's     ENTRYPOINT is used if this is not provided. Variable references $(VAR_NAME)     are expanded using the container's environment. If a variable cannot be     resolved, the reference in the input string will be unchanged. The     $(VAR_NAME) syntax can be escaped with a double $$, ie: $$(VAR_NAME).     Escaped references will never be expanded, regardless of whether the     variable exists or not. Cannot be updated. More info:    https://kubernetes.io/docs/tasks/inject-data-application/define-command-argument-container/#running-a-command-in-a-shell……

2.2 Example

In namespace test in , Define a name frontend Of Pod.

（1） Define the namespace

In order to facilitate later testing , To specify a new namespace test.（ If the namespace test Already exists , There is no need to build ）

Namespace test List of resources file test-namespace.yaml as follows ：

apiVersion: v1kind: Namespacemetadata:     name: test

perform kubectl create  Command to create the Namespace：

[[email protected] ~]$ kubectl create -f test-namespace.yaml namespace/test created

（2） Definition Pod

Define a name frontend Of Pod, It's made up of a container , Resource list file frontend-pod.yaml as follows ：

apiVersion: v1kind: Podmetadata:  name: frontend  namespace: test  labels:    app: frontendspec:  containers:  - name: frontend    image: xcbeyond/vue-frontend:latest    ports:      - name: port        containerPort: 80        hostPort: 8080

perform kubectl create  Command to create the Pod：

[[email protected] ~]$ kubectl create -f frontend-pod.yaml pod/frontend created

Through the command kubectl get pods -n   see , establish Pod The state of ：

[[email protected] ~]$ kubectl get pods -n testNAME       READY   STATUS   RESTARTS   AGEfrontend   1/1     Runing   0          79s