The kubectl command-line utility is a powerful tool.
By default, the kubectl command-line tool interacts with the default namespace. If you want to use a different namespace, you can pass kubectl the --namespace flag.
If you want to change the default namespace more permanently, you can use a context. This gets recorded in a kubectl configuration file, usually located at
$HOME/.kube/config. This configuration file also stores how to both find and authen‐ticate to your cluster. For example, you can create a context with a different default
namespace for your kubectl commands using:
$ kubectl config set-context my-context --namespace=mystuff
To use this newly created context, you can run:
$ kubectl config use-context my-context
Everything contained in Kubernetes is represented by a RESTful resource. Each Kubernetes object exists at a unique HTTP path; for example, https://your-k8s.com/api/v1/name‐spaces/default/pods/my-pod leads to the representation of a Pod in the default name‐ space named my-pod . The kubectl command makes HTTP requests to these URLs to access the Kubernetes objects that reside at these paths.
By default, kubectl uses a human-readable printer for viewing the responses from the API server. One way to get slightly more information is to add the -o wide flag, which gives more details, on a longer line.
Another common task is extracting specific fields from the object. kubectl uses the JSONPath query language to select fields in the returned object. As an example, this command will extract and print the IP address of the specified Pod:
$ kubectl get pods my-pod -o jsonpath --template={.status.podIP}
If you are interested in more detailed information about a particular object, use the describe command:
$ kubectl describe <resource-name> <obj-name>
If you would like to see a list of supported fields for each supported type of Kubernetes object, you can use the explain command:
$ kubectl explain pods
To continuously monitor the state of a particular resource, use the --watch flag with kubectl command.
Objects in the Kubernetes API are represented as JSON or YAML files. These files are either returned by the server in response to a query or posted to the server as part of an API request. You can use these YAML or JSON files to create, update, or delete objects on the Kubernetes server.
Let’s assume that you have a simple object stored in obj.yaml. You can use kubectl to create this object in Kubernetes by running:
$ kubectl apply -f obj.yaml
Similarly, after you make changes to the object, you can use the apply command again to update the object:
$ kubectl apply -f obj.yaml
The apply tool will only modify objects that are different from the current objects in the cluster. If the objects you are creating already exist in the cluster, it will simply exit successfully without making any changes.
You can use the --dry-run flag to print the objects to the terminal without actually sending them to the server.
If you feel like making interactive edits instead of editing a local file, you can instead use the edit command, which will download the latest object state and then launch an editor that contains the definition:
$ kubectl edit <resource-name> <obj-name>
After you save the file, it will be automatically uploaded back to the Kubernetes cluster.
The apply command also records the history of previous configurations in an annotation within the object. You can manipulate these records with the edit-last- applied , set-last-applied , and view-last-applied commands. For example:
$ kubectl apply -f myobj.yaml view-last-applied
When you want to delete an object, you can simply run:
$ kubectl delete -f obj.yaml
Likewise, you can delete an object using the resource type and name:
$ kubectl delete <resource-name> <obj-name>
Labels and annotations are tags for your objects. You can update the labels and annotations on any Kubernetes object using the label and annotate commands. For example, to add the color=red label to a Pod named bar , you can run:
$ kubectl label pods bar color=red
The syntax for annotations is identical.
By default, label and annotate will not let you overwrite an existing label. To do this, you need to add the --overwrite flag.
If you want to remove a label, you can use the <label-name>- syntax:
$ kubectl label pods bar color-
You can use the following to see the logs for a running container:
$ kubectl logs <pod-name>
If you have multiple containers in your Pod, you can choose the container to view
using the -c flag. By default, kubectl logs lists the current logs and exits. If you instead want to
continuously stream the logs back to the terminal without exiting, you can add the -f
(follow) command-line flag.
You can also use the exec command to execute a command in a running container:
$ kubectl exec -it <pod-name> -- bash
You can also copy files to and from a container using the cp command:
$ kubectl cp <pod-name>:</path/to/remote/file> </path/to/local/file>
To forward traffic from the local machine on port 8080 to the remote container on port 80:
$ kubectl port-forward <pod-name> 8080:80
To see a list of the latest 10 events on all objects in a given namespace:
$ kubectl get events
You can also stream events as they happen by adding --watch to the kubectl get
events command. You may also wish to include -A to see events in all namespaces.
You can use the top command to see the list of resources in use by either nodes or Pods. This command:
$ kubectl top nodes
These top commands only work if a metrics server is running in your cluster.