Kubernetes

Kubernetes schedules containers across a cluster and keeps the declared state running. Docker builds and publishes the images; Kubernetes pulls those images and manages Pods, Deployments, Services, ConfigMaps, Secrets, storage, rollout history, and health checks.

Install tools

Install kubectl and choose a local cluster.

kubectl
minikube
kind
Docker Desktop Kubernetes

Start a local minikube cluster with the Docker driver.

minikube start --driver=docker

Check the cluster.

kubectl version --client
kubectl cluster-info
kubectl get nodes

Build and load local images

For local Kubernetes, either push images to a registry or load local images into the cluster.

docker build -t student-rest:local ./flask
minikube image load student-rest:local

With kind, load the image into the named cluster.

kind load docker-image student-rest:local --name kind

Deployment and Service

A Deployment manages replicated Pods. A Service gives those Pods a stable network name and virtual IP.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: student-rest
spec:
  replicas: 2
  selector:
    matchLabels:
      app: student-rest
  template:
    metadata:
      labels:
        app: student-rest
    spec:
      containers:
        - name: rest
          image: student-rest:local
          imagePullPolicy: IfNotPresent
          ports:
            - containerPort: 5000
          readinessProbe:
            httpGet:
              path: /
              port: 5000
          livenessProbe:
            httpGet:
              path: /
              port: 5000
          resources:
            requests:
              cpu: 100m
              memory: 128Mi
            limits:
              cpu: 500m
              memory: 512Mi
---
apiVersion: v1
kind: Service
metadata:
  name: student-rest
spec:
  selector:
    app: student-rest
  ports:
    - port: 80
      targetPort: 5000

Apply the manifest and inspect the workload.

kubectl apply -f student-rest.yaml
kubectl get deployments
kubectl get pods
kubectl get services
kubectl rollout status deployment/student-rest

Forward the Service to the local machine.

kubectl port-forward service/student-rest 8080:80

Open http://localhost:8080.

Rollouts

Deploy a new image by changing the image in the Deployment.

kubectl set image deployment/student-rest rest=student-rest:next
kubectl rollout status deployment/student-rest
kubectl rollout history deployment/student-rest
kubectl rollout undo deployment/student-rest

Configuration and secrets

Use ConfigMaps for non-secret configuration.

kubectl create configmap student-config \
    --from-literal=APP_ENV=local \
    --dry-run=client -o yaml > configmap.yaml

Use Secrets for sensitive values, then mount or expose them to Pods through Kubernetes. Production clusters should integrate with the cloud provider’s secret manager when available.

kubectl create secret generic db-credentials \
    --from-literal=username=student \
    --from-literal=password='change-me' \
    --dry-run=client -o yaml > secret.yaml

Pods and sidecars

A Pod is the smallest Kubernetes scheduling unit. Put multiple containers in one Pod only when they must share lifecycle, network namespace, and storage. A frontend, API, and database should usually be separate Deployments and Services. Sidecars, log shippers, and local proxies are better examples of multi-container Pods.

Operations

These commands are used constantly.

kubectl config get-contexts
kubectl config use-context minikube
kubectl create namespace docker-book
kubectl get all -n docker-book
kubectl describe pod <pod-name> -n docker-book
kubectl logs deployment/student-rest -n docker-book
kubectl exec -it deployment/student-rest -n docker-book -- sh
kubectl delete -f student-rest.yaml

Using local images

The older eval $(minikube docker-env) workflow points the local Docker CLI at the minikube Docker daemon. Prefer minikube image load for new local workflows because it is explicit and works naturally with Buildx-built images.

minikube image load student-rest:local

Useful minikube commands:

minikube dashboard opens the Kubernetes dashboard.
minikube ssh opens a shell on the minikube node.
minikube service <service-name> opens a Service exposed through minikube.
kubectl get events --sort-by=.metadata.creationTimestamp shows recent cluster events.

Removing minikube cluster

Stop minikube. This command effectively halts the virtual machine.

1minikube stop

Delete minikube. This command effectively deletes the virtual machine.

1minikube delete