Kubernetes objects can quickly be created, updated, and deleted directly using imperative commands built into the kubectl command-line tool. This document explains how those commands are organized and how to use them to manage live objects.
Install kubectl.
You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:
To check the version, enterkubectl version. The kubectl tool supports three kinds of object management:
See Kubernetes Object Management for a discussion of the advantages and disadvantage of each kind of object management.
The kubectl tool supports verb-driven commands for creating some of the most common object types. The commands are named to be recognizable to users unfamiliar with the Kubernetes object types.
run: Create a new Pod to run a Container.expose: Create a new Service object to load balance traffic across Pods.autoscale: Create a new Autoscaler object to automatically horizontally scale a controller, such as a Deployment.The kubectl tool also supports creation commands driven by object type. These commands support more object types and are more explicit about their intent, but require users to know the type of objects they intend to create.
create <objecttype> [<subtype>] <instancename>Some objects types have subtypes that you can specify in the create command. For example, the Service object has several subtypes including ClusterIP, LoadBalancer, and NodePort. Here's an example that creates a Service with subtype NodePort:
kubectl create service nodeport <myservicename>
In the preceding example, the create service nodeport command is called a subcommand of the create service command.
You can use the -h flag to find the arguments and flags supported by a subcommand:
kubectl create service nodeport -h
The kubectl command supports verb-driven commands for some common update operations. These commands are named to enable users unfamiliar with Kubernetes objects to perform updates without knowing the specific fields that must be set:
scale: Horizontally scale a controller to add or remove Pods by updating the replica count of the controller.annotate: Add or remove an annotation from an object.label: Add or remove a label from an object.The kubectl command also supports update commands driven by an aspect of the object. Setting this aspect may set different fields for different object types:
set <field>: Set an aspect of an object.The kubectl tool supports these additional ways to update a live object directly, however they require a better understanding of the Kubernetes object schema.
edit: Directly edit the raw configuration of a live object by opening its configuration in an editor.patch: Directly modify specific fields of a live object by using a patch string. For more details on patch strings, see the patch section in API Conventions.You can use the delete command to delete an object from a cluster:
delete <type>/<name>kubectl delete for both imperative commands and imperative object configuration. The difference is in the arguments passed to the command. To use kubectl delete as an imperative command, pass the object to be deleted as an argument. Here's an example that passes a Deployment object named nginx: kubectl delete deployment/nginx
There are several commands for printing information about an object:
get: Prints basic information about matching objects. Use get -h to see a list of options.describe: Prints aggregated detailed information about matching objects.logs: Prints the stdout and stderr for a container running in a Pod.set commands to modify objects before creationThere are some object fields that don't have a flag you can use in a create command. In some of those cases, you can use a combination of set and create to specify a value for the field before object creation. This is done by piping the output of the create command to the set command, and then back to the create command. Here's an example:
kubectl create service clusterip my-svc --clusterip="None" -o yaml --dry-run=client | kubectl set selector --local -f - 'environment=qa' -o yaml | kubectl create -f -
kubectl create service -o yaml --dry-run=client command creates the configuration for the Service, but prints it to stdout as YAML instead of sending it to the Kubernetes API server.kubectl set selector --local -f - -o yaml command reads the configuration from stdin, and writes the updated configuration to stdout as YAML.kubectl create -f - command creates the object using the configuration provided via stdin.--edit to modify objects before creationYou can use kubectl create --edit to make arbitrary changes to an object before it is created. Here's an example:
kubectl create service clusterip my-svc --clusterip="None" -o yaml --dry-run=client > /tmp/srv.yaml
kubectl create --edit -f /tmp/srv.yaml
kubectl create service command creates the configuration for the Service and saves it to /tmp/srv.yaml.kubectl create --edit command opens the configuration file for editing before it creates the object.
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https://kubernetes.io/docs/tasks/manage-kubernetes-objects/imperative-command/