Kubernetes.md

Kubernetes

Kubernetes (commonly stylized as k8s) is an open-source container-orchestration system for automating application deployment, scaling, and management.

Why?

• High availability or no downtime
• Scalability or high performance
• Disaster recovery (backup and restore)

Architecture

Some definitions

Inside Worker Nodes: Service: Ensures permanent IP even when pods die
Ingress: For external services with secure protocol and domain name
ConfigMap: Contains configurations to prevent having to rebuild pods on changes
Secret: Configmap with base64 encoding
Volumes: Ensures data persistence through attaching physical storage (local or remote)
Deployment: Abstraction of pods that ensures uptime through replication of nodes
StatefulSet: Sort of advanced deployment that can handle state for databases

Installation (windows)

Hyper-V

Enable-WindowsOptionalFeature -Online -FeatureName Microsoft-Hyper-V -All

MiniKube

choco install minikube

Kubectl

choco install kubernetes-cli

Start Virtual Minikube Cluster

minikube start --driver=hyperv
minikube status

kubectl get nodes
kubectl version
kubectl get services

Create pods

Create a pod

kubectl create deployment deploymentNAME --image=mongo
kubectl get deployment
kubectl get pod
kubectl describe pod podNAME
kubectl logs podNAME

Creating a Configured Deployment

kubectl apply -f fileNAME.yaml

Interactive Terminal

kubectl exec -it podID bin/bash

Delete pods

Delete a pod

kubectl delete pod podNAME

Delete all pods

kubectl delete --all pods

Delete a deployment

kubectl delete deployment deploymentNAME

Delete all deployments

kubectl delete --all deployments

Simple example

Create nginx-deployment.yaml containing:

apiVersion: apps/v1
kind: Deployment
metadata:
    name: nginx-deployment
    labels:
        app: nginx
spec:
    replicas: 2 
    selector:
        matchLabels:
            app: nginx
    template:
        metadata:
            labels:
                app: nginx
        spec:
            containers:
            - name: nginx
              image: nginx:1.16
              ports:
              - containerPort: 80  

kubectl apply -f nginx-deployment.yaml
~ created
kubectl get deployment
kubectl get pod

Edit nginx-deployment.yaml ...

kubectl apply -f nginx-deployment.yaml
~ configured

Example Mongo Application

Create Deployment

Create mongo.yaml containing:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: mongodb-deployment
  labels:
    app: mongodb
spec:
  replicas: 1
  selector:
    matchLabels:
      app: mongodb
  template:
    metadata:
      labels:
        app: mongodb
    spec:
      containers:
        - name: mongodb
          image: mongo
          ports:
            - containerPort: 27017
          env:
            - name: MONGO_INITDB_ROOT_USERNAME
              valueFrom:
                secretKeyRef:
                  name: mongodb-secret
                  key: mongo-root-username
            - name: MONGO_INITDB_ROOT_PASSWORD
              valueFrom: 
                secretKeyRef:
                  name: mongodb-secret
                  key: mongo-root-password

Create Secret

Create mongo-secret.yaml containing:

apiVersion: v1
kind: Secret
metadata:
    name: mongodb-secret
type: Opaque
data:
    mongo-root-username: dXNlcm5hbWU=
    mongo-root-password: cGFzc3dvcmQ=

Encode:

[Convert]::ToBase64String([System.Text.Encoding]::UTF8.GetBytes('username'))

Decode:

[System.Text.Encoding]::UTF8.GetString([System.Convert]::FromBase64String('cGFzc3dvcmQ='))

Applying secret:

kubectl apply -f mongo-secret.yaml
kubectl apply -f mongo.yaml
kubectl get pod --watch
kubectl describe pod podNAME

Create Internal Service

Append to mongo.yaml:

---
apiVersion: v1
kind: Service
metadata:
  name: mongodb-service
spec:
  selector:
    app: mongodb
  ports:
    - protocol: TCP
      port: 27017
      targetPort: 27017

kubectl apply -f mongo.yaml
kubectl get service
kubectl descibe service serviceNAME
kubectl get pod -o wide

To see all components about mongodb

kubectl get all | grep mongodb

Create Mongo Express Deployment

Create mongo-express.yaml containing:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: mongo-express
  labels:
    app: mongo-express
spec:
  replicas: 1
  selector:
    matchLabels:
      app: mongo-express
  template:
    metadata:
      labels:
        app: mongo-express
    spec:
      containers:
      - name: mongo-express
        image: mongo-express
        ports:
        - containerPort: 8081
        env:
        - name: ME_CONFIG_MONGODB_ADMINUSERNAME
          valueFrom:
            secretKeyRef:
              name: mongodb-secret
              key: mongo-root-username
        - name: ME_CONFIG_MONGODB_ADMINPASSWORD
          valueFrom:
            secretKeyRef:
              name: mongodb-secret
              key: mongo-root-password
        - name: ME_CONFIG_MONGODB_SERVER
          valueFrom:
            configMapKeyRef:
              name: mongodb-configmap
              key: database_url

Create ConfigMap

Create mongo-configmap.yaml containing:

apiVersion: v1
kind: ConfigMap
metadata:
    name: mongodb-configmap
data:
    database_url: mongodb-service

kubectl apply -f mongo-configmap.yaml
kubectl apply -f mongo-express.yaml

Create External Service

Append to mongo-express.yaml:

---
apiVersion: v1
kind: Service
metadata:
  name: mongo-express-service
spec:
  selector:
    app: mongo-express
  type: LoadBalancer
  ports:
    - protocol: TCP
      port: 8081
      targetPort: 8081
      nodePort: 30000

kubectl apply -f mongo-express.yaml
kubectl get service
kubectl describe service mongodb-service
kubectl get pod -o wide
kubectl describe pod podID
kubectl logs podID

Serve Mongo Express

minikube service mongo-express-service