Core Concepts

Kubernetes API Primitives¶

Kubernetes API primitive, also known as Kubernetes objects, are the basic building blocks of any application running in Kubernetes

Examples: - Pod - Node - Service - ServiceAccount

Two primary members - Spec, desired state - Status, current state

Resources¶

OpenShift - Pods - Nodes

IKS - Objects - Kube Basics

References¶

oc api-resources

oc api-resources -o wide

oc api-resources -o name

oc get nodes,ns,po,deploy,svc

oc describe node 

kubectl api-resources

kubectl api-resources -o wide

kubectl api-resources -o name

kubectl get nodes,ns,po,deploy,svc

kubectl describe node --all

Creating Pods¶

A Pod is the basic execution unit of a Kubernetes application–the smallest and simplest unit in the Kubernetes object model that you create or deploy. A Pod represents processes running on your Cluster.

A Pod encapsulates an application’s container (or, in some cases, multiple containers), storage resources, a unique network IP, and options that govern how the container(s) should run. A Pod represents a unit of deployment: a single instance of an application in Kubernetes, which might consist of either a single container or a small number of containers that are tightly coupled and that share resources.

Resources¶

OpenShift - About Pods - Cluster Configuration for Pods - Pod Autoscaling

IKS - Pod Overview - Pod Lifecycle - Pod Usage

References¶

apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
  labels:
    app: myapp
spec:
  containers:
  - name: myapp-container
    image: busybox
    command: ['sh', '-c', 'echo Hello Kubernetes! && sleep 3600']

oc get pods

oc describe pod <pod-name>

oc get pods -o wide

oc adm top pods

kubectl get pods

kubectl describe pod <pod-name>

kubectl delete pod <pod-name>

kubectl edit pod <pod-name>

Projects/Namespaces¶

Namespaces are intended for use in environments with many users spread across multiple teams, or projects.

Namespaces provide a scope for names. Names of resources need to be unique within a namespace, but not across namespaces.

Namespaces are a way to divide cluster resources between multiple users (via resource quota).

It is not necessary to use multiple namespaces just to separate slightly different resources, such as different versions of the same software: use labels to distinguish resources within the same namespace. In practice namespaces are used to deploy different versions based on stages of the CICD pipeline (dev, test, stage, prod)

Resources¶

OpenShift - Working With Projects - Creating Projects - Configure Project Creation

IKS - Namespaces

References:¶

apiVersion: v1
kind: Namespace
metadata:
  name: foo

apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
  namespace: bar
  labels:
    app: myapp
spec:
  containers:
  - name: myapp-container
    image: busybox
    command: ['sh', '-c', 'echo Hello Kubernetes! && sleep 3600']

oc new-project my-project

oc project

oc status

kubectl get namespaces

kubectl create ns bar

kubectl set-context --current --namespace=bar