Container Orchestration - Introduction to Kubernetes

What is Container Orchestration

Container orchestration is a technology that automates the placement, scaling, networking, and availability management of multiple containers. It’s essential for running numerous containers in production environments.

Why is it needed: While a few containers can be managed manually, hundreds or thousands of containers require automated systems for placement, failure detection, and scaling.

Problems Orchestration Solves

Basic Kubernetes Architecture

flowchart TB
    subgraph ControlPlane["Control Plane"]
        API["API Server"]
        Sched["Scheduler"]
        CM["Controller Manager"]
        etcd["etcd"]
    end

    subgraph Worker1["Worker Node 1"]
        K1["kubelet"]
        KP1["kube-proxy"]
        P1["Pod"]
        P2["Pod"]
    end

    subgraph Worker2["Worker Node 2"]
        K2["kubelet"]
        KP2["kube-proxy"]
        P3["Pod"]
        P4["Pod"]
    end

    subgraph Worker3["Worker Node 3"]
        K3["kubelet"]
        KP3["kube-proxy"]
        P5["Pod"]
        P6["Pod"]
    end

    ControlPlane --> Worker1
    ControlPlane --> Worker2
    ControlPlane --> Worker3

Control Plane

• API Server: Entry point for all cluster operations
• Scheduler: Determines which node to run Pods on
• Controller Manager: Controllers that maintain desired state
• etcd: Distributed KVS storing cluster state

Worker Node

• kubelet: Manages Pods on the node
• kube-proxy: Network proxy and load balancing

Main Resources

Pod

The smallest deployment unit in Kubernetes. Groups one or more containers together.

apiVersion: v1
kind: Pod
metadata:
  name: my-app
  labels:
    app: web
spec:
  containers:
    - name: app
      image: nginx:1.25
      ports:
        - containerPort: 80
      resources:
        requests:
          memory: "64Mi"
          cpu: "250m"
        limits:
          memory: "128Mi"
          cpu: "500m"

Deployment

Manages Pod replicas and rolling updates.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: web
  template:
    metadata:
      labels:
        app: web
    spec:
      containers:
        - name: web
          image: my-app:1.0.0
          ports:
            - containerPort: 8080
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 0

Service

Provides stable network access to Pods.

apiVersion: v1
kind: Service
metadata:
  name: web-service
spec:
  selector:
    app: web
  ports:
    - port: 80
      targetPort: 8080
  type: ClusterIP

Service Types

ConfigMap / Secret

Manages configuration and sensitive information.

# ConfigMap
apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  DATABASE_HOST: "db.example.com"
  LOG_LEVEL: "info"

---
# Secret
apiVersion: v1
kind: Secret
metadata:
  name: app-secrets
type: Opaque
data:
  DATABASE_PASSWORD: cGFzc3dvcmQxMjM=  # base64 encoded

# Usage in Pod
spec:
  containers:
    - name: app
      envFrom:
        - configMapRef:
            name: app-config
        - secretRef:
            name: app-secrets

Scaling

Manual Scaling

kubectl scale deployment web-deployment --replicas=5

Auto Scaling (HPA)

apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  name: web-hpa
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: web-deployment
  minReplicas: 2
  maxReplicas: 10
  metrics:
    - type: Resource
      resource:
        name: cpu
        target:
          type: Utilization
          averageUtilization: 70

Rolling Updates

# Update image
kubectl set image deployment/web-deployment web=my-app:2.0.0

# Check update status
kubectl rollout status deployment/web-deployment

# Rollback
kubectl rollout undo deployment/web-deployment

Health Checks

spec:
  containers:
    - name: app
      livenessProbe:
        httpGet:
          path: /healthz
          port: 8080
        initialDelaySeconds: 10
        periodSeconds: 5
      readinessProbe:
        httpGet:
          path: /ready
          port: 8080
        initialDelaySeconds: 5
        periodSeconds: 3

• livenessProbe: Restarts container on failure
• readinessProbe: Removes from Service on failure

Summary

Kubernetes is a powerful platform that automates the operation of containerized applications. By understanding basic resources like Pods, Deployments, and Services and combining them appropriately, you can build scalable and highly available systems.