Declaratively create a kubernetes pod using kubectl (for docker administrators)

The first thing one want to try once we have access to a Kubernetes cluster is to run a pod in it. Let's try to create our first pod on kubernetes, declaratively: meaning that we will be writing a manifest to do it.

For the ones that are familiarized with docker what we are trying to do is equivalent to the following docker run command:

docker run -dt nginx

To do this on a kubernetes cluster we will have create a pod manifest using yaml:

apiVersion: v1
kind: Pod
metadata:
  name: demo
spec:
  containers:
  - name: container
    image: nginx

Using this manifest we are telling the kubernetes cluster that a kind: Pod resource needs to be created, it's name is name: demo and we want it to be composed of containers:, which in this case is just one container named - name: container using the image image: nginx.

To be able to apply this manifest we will have to use kubectl apply with the file containing this manifest like so:

$ kubectl apply -f /tmp/pod.yaml 
pod/demo created

On docker, to check whether the container have been created we would use docker ps:

$ docker ps
CONTAINER ID   IMAGE                          COMMAND                  CREATED         STATUS                  PORTS                    NAMES
bbf4ccca3dc0   nginx                          "/docker-entrypoint.…"   7 seconds ago   Up 2 seconds            80/tcp                   xenodochial_khayyam

On a kubernetes cluster it's most close equivalent would be kubectl get pods. Once the the kubectl apply have been issues it's going to take a while to get the pod up and runnig, here is what it looks like when the pod is still being created:

$ kubectl get pods
NAME                                     READY   STATUS              RESTARTS   AGE
demo                                     0/1     ContainerCreating   0          9s

Once it's reade we will see the STATUS column that changes to Running:

$ kubectl get pods
NAME                                     READY   STATUS              RESTARTS   AGE
demo                                     1/1     Running     0          27s

Posted on 31/03/2021