K8s Commands

K8s Commands

Types of Commands

Kubernetes supports imperative and declarative approaches for managing resources

Imperative Commands

You’re explicitly telling the cluster what to do, without describing the complete desired state.
It’s like giving step-by-step directions.

Command	Description	Example
`kubectl get <resource>`	List resources like pods, services, etc.	`kubectl get pods`
`kubectl describe <resource>`	Show detailed information about a resource.	`kubectl describe pod my-pod`
`kubectl create <resource>`	Create a resource from a file or stdin.	`kubectl create -f my-deployment.yaml`
`kubectl delete <resource>`	Delete resources by filenames, stdin, or resource names.	`kubectl delete pod my-pod`
`kubectl apply <resource>`	Apply changes to resources from a file or stdin.	`kubectl apply -f my-deployment.yaml`
`kubectl exec`	Execute a command in a container.	`kubectl exec my-pod -- ls /`
`kubectl logs`	Print the logs for a container in a pod.	`kubectl logs my-pod`
`kubectl scale`	Scale the replicas of a deployment or replicaset.	`kubectl scale --replicas=5 deployment/my-app`
`kubectl port-forward`	Forward one or more local ports to a pod.	`kubectl port-forward my-pod 8080:8080`
`kubectl rollout`	Manage the rollout of a resource.	`kubectl rollout undo deployment/my-deployment`
`kubectl label`	Update or add labels to a resource.	`kubectl label pods my-pod status=unhealthy`
`kubectl annotate`	Add or update annotations to a resource.	`kubectl annotate pods my-pod description="test"`
`kubectl config`	Modify kubeconfig files.	`kubectl config set-context my-context`
`kubectl cluster-info`	Display cluster info.	`kubectl cluster-info`
`kubectl top`	Display resource usage (CPU/Memory) for nodes or pods.	`kubectl top nodes`

These commands cover most of the everyday tasks you would perform with Kubernetes, from managing resources to viewing logs and scaling applications.
Remember to replace <resource> with the actual resource type and name you want to interact with!

Declarative Commands

You’re providing the desired state in a file, and Kubernetes figures out how to get there.
It’s like providing a destination, and letting the system decide the path.
The declarative approach typically revolves around using the kubectl apply command with various manifest files.

Command	Description
`kubectl apply -f <filename.yaml>`	Apply the configuration in `<filename.yaml>` to the resource.
`kubectl apply -f <directory/>`	Apply the configurations in all YAML or JSON files within a directory.
`kubectl apply -k <kustomization>`	Apply a kustomization directory.
`kubectl delete -f <filename.yaml>`	Delete the resources defined in `<filename.yaml>`.
`kubectl diff -f <filename.yaml>`	Diff the local resource with the running configuration.
`kubectl replace -f <filename.yaml>`	Replace the resource with the configuration in `<filename.yaml>`.

This approach ensures the configuration files are the source of truth, and the desired state is maintained.
The declarative approach is preferred for:
- Managing complex configuration
- Maintaining consistency across environments
- Leveraging version control practices

Comparison

Aspect	Imperative Commands	Declarative Commands
Definition	Commands that manage resources by direct action.	Commands that manage resources based on manifest files.
Usage	Utilized for one-off tasks, quick edits, or experimentation.	Used for maintaining the desired state as defined in files.
Command Examples	`kubectl create`, `kubectl run`, `kubectl expose`	`kubectl apply -f <filename.yaml>`
File Requirement	No YAML or JSON file required.	Requires YAML or JSON file describing the desired state.
Flexibility	Limited in complex scenarios.	More flexible and can handle complex configurations.
State Tracking	No automatic tracking of the current state.	Can track the current state and make updates as needed.
Recommended For	Ad-hoc actions and prototyping.	Production environments, version control, and collaboration.