Kubernetes quick notes deployment (WIP)

As opposed to docker that operates on the container level directly, kubernetes has a different approach as such there are a set of steps required to get the application running into the cluster. For example, in docker a simple docker run creates the container and starts it. In kubernetes, first we need to create a deployment and then expose it.

Creating a pod

A pod is the smallest unit on the kubernetes cluster. Pods are a group of containers that are related to each other.

Manually

It’s not possible to run an empty pod, it is required to have an image.

kubectl run my-pod-name --image=my-image

Side note: for deleting the created pod, k8s expects the prefix pods/ (issuing the delete command without the prefix spawn the error message: error: the server doesn't have a resource type "my-pod-name"), in this case the full name to delete the pod would be: pods/my-pod-name.

Fetching the information about the created pods, can be achieved in two ways, with less details:

kubectl get pods

Another options to list more details would be:

kubectl describe pods my-pod-name

Side node: the name of the pod is options, in this case my-pod-name could be removed.

Another helpful command to check the container running is to access it via browser or any other client, for that the port-forward is used:

kubectl port-forward my-pod-name container-port:local-port

Deployments

Creating a deployment

kubectl create deployment my-deployment-name --image=my-image

Exposing the deployment

kubectl expose deployment my-deployment-name

Managing containers

Therefore, it is possible to use kubernetes with the same docker behavior, for example the kubectl run command is available for that. The attention point is the need to have a pod. In other words, in docker you can run a container with docker run, but in kubernetes you need a pod before that. The analogy that [1] uses for describing how kubernetes handles the different layers of abstraction is as follows:

  • A Deployment manages a ReplicaSet
  • A ReplicaSet manages a Pod
  • A Pod is an abstraction of a Container

References

  1. [1]Nana, “Kubernetes Tutorial for Beginners [FULL COURSE in 4 Hours],” 2021 [Online]. Available at: https://www.youtube.com/watch?v=X48VuDVv0do. [Accessed: 06-Nov-2020]