Abdullah Şamil Güser

Kubernetes a.k.a. K8s Concepts

What is Kubernetes?

• K&s is the leading container orchestration tool
• Designed as a loosely coupled collection of components centered around deploying, maintaining and scaling workloads
• Vendor-neutral : Runs on all cloud providers
• Backed by a huge community

What K&s can do

• Service discovery and load balancing
• Storage orchestration : Local or Cloud based
• Automated rollouts and rollbacks
• Self-healing
• Secret and configuration management
• Use the same API across on-premise and every cloud providers

What K&s can’t do

• Does not deploy source code
• Does not build your application
• Does not provide application-level services : Message buses, databases, caches, etc

K&s Architecture

 --------------------
|  Cluster           |
|  ---------------   |
| |  Node         |  |
| |  ---------    |  |
| | |  Pod    |   |  |
| |  ---------    |  |
|  ---------------   |
 --------------------

Local K8s

Docker Desktop

• Requires virtualization
  • Docker Desktop
  • MicroK8s
  • Minikube
• Runs over Docker Desktop
  • Kind
• Limited to 1 node
  • Docker Desktop
• Multiple nodes
  • MicroK8s
  • Kind
  • Minikube

Windows

• Docker Desktop is currently the only way to run both Linux and Windows containers
• Docker Desktop can run on Hyper-V or WSL 2 (Win 10 2004)
• If Hyper-V is enabled, you can’t run another hypervisor at the same time
• You can install Minikube on Hyper-V or VirtualBox

Minikube

• Does not require Docker Desktop
• Installs on Linux, macOS and Windows
  • https://kubernetes.io/docs/tasks/tools/install-minikube/
• An Hypervisor like VirtualBox is required
• install using brew in macOS

Test Kubernetes Locally

kubectl cluster-info

K8s CLI & Context

K8s API

• Kubernetes API server is a service running on the master node.
• It exposes a rest API that is the only point of communication for kubernetes clusters
• We define the desired state in yaml files
• Let’s say we want to run X number of instances of a container in the cluster
• We then send that desired state to the cluster via the rest API
• Other applications like a web dashboard can also communicate with the rest API to display the cluster state

K8s CLI

• kubectl is the CLI to interact with the cluster
• Communicates with the apiserver
• Configuration stored locally

    ${HOME}/.kube/config
    C:\Users\{USER}\.kube\config
  

K8s Context

• A context is a group of access parameters to a K8s cluster
• Contains a Kubernetes cluster, a user, and a namespace
• The current context is the cluster that is currently the default for kubectl
  • All kubectl commands run against that cluster

kubectl - Context Cheat Sheet

kubectl config current-context               # Get the current context
kubectl config get-contexts                  # List all context
kubectl config use-context [contextName]     # Change/Set the current context
kubectl config delete-context [contextName]  # Delete a context from the config file

kubectx - Quickly swithc context

• Instead of typing kubectl config use-context minikube
• Simply type kubectx [contextName]
• macOS brew install kubectx
• Ubuntu sudo apt install kubectx (https://github.com/ahmetb/kubect)

2 ways to create resources

The declarative way vs the imperative way

Imperative

• Using kubectl commands, issue a series of commands to create resources
• Great for learning, testing and troubleshooting
• It’s like code

Declarative

• Using kubectl and YAML manifests defining the resources that you need
• Reproducible, repeatable
• Can be saved in source control
• It’s like data that can be parsed and modified

What’s a YAML file?

• It’s a text file that contains properties that define the resource
• It has some required properties like the API version the object kind that defines the type of object you want to create
• Root level required properties
  • apiVersion
    • Api version of the object
  • kind
    • type of object
  • metadata.name
    • unique name for the object
  • metadata.namespace
    • scoped environment name (will default to current)
  • spec
    • object specifications or desired state
• You can use the kubectl create command to send the information to the kubernetes cluster

  kubectl create -f [YAML file]
  

Declarative vs Imperative example : L18-04