Introduction to Kubernetes

Key Kubernetes Concepts

Pods

Pods are the smallest deployable units in Kubernetes:

• Group of one or more containers with shared storage and network resources
• Containers in a pod share an IP address and port space
• Containers in a pod can communicate via localhost
• Pods are ephemeral—they can be terminated and replaced anytime

# Example Pod YAML
apiVersion: v1
kind: Pod
metadata:
  name: nginx-pod
  labels:
    app: nginx
spec:
  containers:
  - name: nginx
    image: nginx:1.19
    ports:
    - containerPort: 80

Services

Services provide network access to a set of pods:

• Stable IP address and DNS name for accessing a group of pods
• Load balancing between pods
• Service discovery for pods that come and go
• Different types: ClusterIP, NodePort, LoadBalancer, ExternalName

# Example Service YAML
apiVersion: v1
kind: Service
metadata:
  name: nginx-service
spec:
  selector:
    app: nginx
  ports:
  - port: 80
    targetPort: 80
  type: ClusterIP

Deployments

Deployments manage the lifecycle of pods:

• Declare desired state for replica pods
• Handle rolling updates and rollbacks
• Scale the number of replicas
• Create and manage ReplicaSets

# Example Deployment YAML
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.19
        ports:
        - containerPort: 80

Namespaces

Namespaces provide isolation and organization within a cluster:

• Virtual clusters inside a physical cluster
• Useful for multi-tenant environments
• Resources named uniquely within a namespace
• Default namespaces: default, kube-system, kube-public, kube-node-lease

# Example Namespace YAML
apiVersion: v1
kind: Namespace
metadata:
  name: development

ConfigMaps and Secrets

Store configuration and sensitive data:

• ConfigMaps: Store non-sensitive configuration data
• Secrets: Store sensitive information (base64 encoded)
• Can be mounted as files or environment variables
• Decouple configuration from container images

# Example ConfigMap YAML
apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  database_url: "postgres://postgres:5432/mydb"
  cache_ttl: "300"

# Example Secret YAML
apiVersion: v1
kind: Secret
metadata:
  name: app-secrets
type: Opaque
data:
  db_password: cGFzc3dvcmQxMjM=  # base64 encoded "password123"
  api_key: dGhpc2lzYXNlY3JldGtleQ==  # base64 encoded "thisisasecretkey"