Operation modes of kubectl

Imperative

• I would tell kubectl what action has to be taken

kubectl run tomcat --image=tomcat:8

Declarative

• Maintaining declared state.
• Declarative state is mentioned in some file.
• To describe Declarative State in k8s we use YAML files.
• Lets assume you have yaml file test.yml.

kubctl apply -f test.yml
kubectl delete -f test.yml

Kubernetes APIs

• All capabilities of K8s are exposed as REST APIs
• To execute APIs
  • kubectl
  • Client Libraries
• APIs are changing every day, then how should i use in my Production Systems.

API Versions

• Are of three types
  • Alpha: inside api version if you see alpha
  • Beta: inside api version if you see beta
  • Stable: inside api version if you see vX here X is a integer

API groups

Refer here for more info

Resources and Objects

• Resources are all the possibilities in K8s
• Objects are what you are creating

Commands

kubectl api-versions

Resource Category Workload

• Pod:

  • smallest unit of creation in k8s
  • Pod has
    • Container(s)
    • Storage
    • IP Address

• Controller

Kubernetes Objects

• Object has two nested groups

  • Object Spec:

    • input
    • Desired state

  • Object Status:

    • output
    • Actual State
• Syntax:

apiVersion: <apiversion>
kind: <type>
metadata: 
    key1: <value1>
spec: <objectspec>