According to the docs:
https://kubernetes.io/docs/reference/generated/kubectl/kubectl-commands#run
kubectl run NAME --image=image
will run an image.
Some questions:
I assume this is a pod rather than a container?
And I assume NAME is associated with the pod?
Snowcrash, you are correct. This is basically the same as docker run command. So using kubectl run NAME --image=image will exactly run a pod named NAME from docker image called image.
You can check what exactly is happening by using kubectl describe pod NAME
Here is an example of kubectl run nginx --image=nginx
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Warning FailedScheduling 89s (x2 over 89s) default-scheduler 0/2 nodes are available: 2 node(s) had taints that the pod didn't tolerate.
Normal Scheduled 19s default-scheduler Successfully assigned default/nginx-7cdbd8cdc9-glkxq to centos-master
Normal Pulling 18s kubelet, centos-master pulling image "nginx"
Normal Pulled 14s kubelet, centos-master Successfully pulled image "nginx"
Normal Created 14s kubelet, centos-master Created container
Normal Started 14s kubelet, centos-master Started container
So what happened after kubectl run is:
Scheduler was trying to pick a node to launch the container (at first it failed due to a taints, because my node is in NotReady state (not important at the moment, but you can read more about it here)
Scheduler successfully assigned the pod to the node (centos-master).
The kubelet checks if the docker image is available and pulls it if necessary.
Then the container is created and started.
*here you can find an interesting article which explains this in a little more detailed way.
The name is associated with pod, because Pod is the smallest unit of work in Kubernetes. Each pod can contain one or more containers. All the containers in the Pod have the same IP address and port space, can access shared storage on the Node hosting that pod.
Basically the kubectl command-line tool supports several different ways to create and manage Kubernetes objects:
*you can find more about them in this StackOverflow answer or this Medium article.
run command is an example of imperative approach. Is the simplest to start
[...] Because this technique operates directly on live objects, it provides no history of previous configurations.
The kubectl run NAME --image=image command, will raise a pod (by creating a corresponding deployment and replication set for given image) with name NAME using the image named image. Think of name here as the tag name in Docker.
Then, when you run kubectl get pods, you will see a pod with name NAME in list.
Using kubectl get all will fetch all resources in default name space (which will also list the deployment and replication set object)
Example :
$ kubectl run nginx --image=nginx
$ kubectl get all
NAME READY STATUS RESTARTS AGE
pod/nginx-6db489d4b7-cs748 0/1 ContainerCreating 0 6s
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 31d
NAME READY UP-TO-DATE AVAILABLE AGE
deployment.apps/nginx 0/1 1 0 6s
NAME DESIRED CURRENT READY AGE
replicaset.apps/nginx-6db489d4b7 1 1 0 6s
If you are looking to create just a pod with no additional deployment and replication controller objects use below imerative command
kubectl run NAME --image=image --restart=Never
when you list result of above command (refer below output) you should see only the corresponding pod (no deployment and replication set object are created)
$ kubectl run nginx --image=nginx --restart=Never
pod/nginx created
$ kubectl get all
NAME READY STATUS RESTARTS AGE
pod/nginx 0/1 ContainerCreating 0 3s
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 31d
