Kubernetes Learning Path (11) resource list definition

First, Kubernetes common resources

The following is an object in Kubernetes, which can be configured as an API type in a Yaml file.

Category	Name
Workload-based resource objects	Pod replicaset replicationcontroller deployments statefulsets daemonset Job cronjob
Service Discovery and load balancing	Service Ingress
Configuration and Storage	Volume, persistent Volume, CSl, Configmap, secret
Cluster resources	Namespace Node Role clusterrole rolebinding clusterrolebinding
Meta Data resources	HPA podtemplate Limitrang

Ii. understanding the objects in Kubernetes

In the Kubernetes system, the Kubernetes object is a persisted entry. Kubernetes uses these entries to represent the state of the entire cluster. In particular, they describe the following information:

• What container applications are running (and on which Node)
• Resources that can be used by the app
• Strategies for how applications behave, such as restart policies, upgrade strategies, and fault tolerance strategies

The Kubernetes object is a "target record"--once the object is created, the Kubernetes system will continue to work to ensure that the object exists. By creating an object, you can effectively tell the Kubernetes system what the cluster workload looks like, which is the desired state of the Kubernetes cluster.

Working with Kubernetes objects-whether created, modified, or deleted-requires the use of the Kubernetes API. When using the kubectl command-line interface, for example, the CLI uses the necessary Kubernetes API calls, or it can use the Kubernetes API directly in the program.

Third, the object of the spec and state

Each Kubernetes object contains two nested object fields, which are responsible for managing the configuration of objects: Object spec and object status. Spec must provide, which describes the desired state of an object-the characteristics of the desired object. Status describes the actual state of the object, which is provided and updated by the Kubernetes system. At any given moment, the Kubernetes control plane is active, managing the actual state of the object to match the state we expect.

For example, the Kubernetes Deployment object can represent an application running in a cluster. When creating a Deployment, you may need to set the Deployment spec to specify that the app requires 3 copies to run. The Kubernetes system reads the Deployment spec and launches 3 instances of the application that we expect-updating the status to match the spec. If there are failures (a state change) in those instances, the Kubernetes system responds to the inconsistency between spec and state by correcting-in this case, a new instance is started to replace.

Iv. Defining resources Using YAML

When creating a Kubernetes object, you must provide a spec for the object that describes the expected state of the object and some basic information about the object (for example, name). When an object is created using the Kubernetes API (or created directly, or based on kubectl ), the API request must contain the JSON-formatted information in the request body. More commonly, this information needs to be provided in the. yaml file for Kubectl. kubectlthis information is converted to JSON format when the API request is executed. As an example:

 [[email protected] ~]# vim my-demo.yaml apiVersion:v1kind:Podmetadata:name: My -demo namespace:default labels:name:myapp tier:appfrontspec:containers  : - Name:myapp image:ikubernetes /myapp:v1 - name:busybox image:busybox command: - " /bin/sh  " -"  -c   "-"  sleep 3600   " [[email protected] -master ~]# kubectl apply-f my-demo.yaml 

In the file that corresponds to the Kubernetes object you want to create .yaml , you need to configure the following fields:

• apiVersion-The version of the Kubernetes API used to create the object
• kind-The type of object you want to create
• metadata-data that helps identify object uniqueness, including a name string, UID, and optionalnamespace

You can view deployment resource-defined fields in a kubectl explain way

[[Email protected] ~]# kubectl Explain deployment #查看deployment的定义字段, contains the require tag is a must field KIND:DeploymentVERSION:extensions/v1beta1description:deprecated-This group version of Deployment was deprecated by apps/v1beta2/deployment. See the Release Notes for  Moreinformation. Deployment Enables declarative updates forPods and ReplicaSets.FIELDS:apiVersion<string>Apiversion defines the versioned schema of this representation of aObject. Servers should convert recognized schemas to the latest internal value, and may reject unrecognized values. moreInfo: https://git.k8s.io/community/contributors/devel/api-conventions.md#resourcesKind<string>Kind is astringValue representing the REST resource thisObjectrepresents. Servers may infer this from the endpoint, the client submits requests to. cannot be updated. In CamelCase. moreInfo: https://Git.k8s.io/community/contributors/devel/api-conventions.md#types-kindsmetadata<Object> StandardObjectmetadata. Spec<Object>specification of the desired behavior of the Deployment. Status<Object>Most recently observed status of the Deployment.

Kubernetes Learning Path (11) resource list definition