Kubernetes Resources

Understanding Kubernetes resource types and their relationships.

Core Resources

Pods

The smallest deployable unit in Kubernetes:

apiVersion: v1 kind: Pod metadata: name: my-pod spec: containers:

• name: app image: nginx:1.21

ReplicaSets

Maintains a stable set of replica Pods:

apiVersion: apps/v1 kind: ReplicaSet metadata: name: my-replicaset spec: replicas: 3 selector: matchLabels: app: my-app template: # Pod template

Deployments

Manages ReplicaSets and provides declarative updates:

apiVersion: apps/v1 kind: Deployment metadata: name: my-deployment spec: replicas: 3 strategy: type: RollingUpdate rollingUpdate: maxSurge: 1 maxUnavailable: 0

...

Networking Resources

Services

Exposes Pods to network traffic:

• ClusterIP: Internal cluster access only

• NodePort: Exposes on each Node's IP

• LoadBalancer: Cloud provider load balancer

• ExternalName: DNS CNAME record

apiVersion: v1 kind: Service metadata: name: my-service spec: type: ClusterIP selector: app: my-app ports:

• port: 80 targetPort: 8080

Ingress

HTTP/HTTPS routing to services:

apiVersion: networking.k8s.io/v1 kind: Ingress metadata: name: my-ingress spec: rules:

• host: myapp.example.com http: paths:
  • path: / pathType: Prefix backend: service: name: my-service port: number: 80

Storage Resources

PersistentVolume

Cluster-level storage resource:

apiVersion: v1 kind: PersistentVolume metadata: name: my-pv spec: capacity: storage: 10Gi accessModes:

• ReadWriteOnce persistentVolumeReclaimPolicy: Retain storageClassName: standard

PersistentVolumeClaim

Request for storage:

apiVersion: v1 kind: PersistentVolumeClaim metadata: name: my-pvc spec: accessModes:

• ReadWriteOnce resources: requests: storage: 5Gi storageClassName: standard

Configuration Resources

ConfigMaps

Non-sensitive configuration data:

apiVersion: v1 kind: ConfigMap metadata: name: app-config data: config.json: | { "key": "value" }

Secrets

Sensitive information:

apiVersion: v1 kind: Secret metadata: name: app-secret type: Opaque stringData: username: admin password: secret123

Workload Resources

StatefulSet

For stateful applications:

apiVersion: apps/v1 kind: StatefulSet metadata: name: web spec: serviceName: "nginx" replicas: 3 selector: matchLabels: app: nginx template: # Pod template volumeClaimTemplates:

• metadata: name: www spec: accessModes: [ "ReadWriteOnce" ] resources: requests: storage: 1Gi

DaemonSet

Runs a Pod on every Node:

apiVersion: apps/v1 kind: DaemonSet metadata: name: monitoring-agent spec: selector: matchLabels: name: monitoring-agent template: # Pod template

Job

Run-to-completion tasks:

apiVersion: batch/v1 kind: Job metadata: name: batch-job spec: template: spec: containers: - name: job image: busybox command: ["echo", "Hello"] restartPolicy: Never backoffLimit: 4

CronJob

Scheduled jobs:

apiVersion: batch/v1 kind: CronJob metadata: name: scheduled-job spec: schedule: "0 0 * * *" jobTemplate: spec: template: spec: containers: - name: job image: busybox command: ["echo", "Daily task"] restartPolicy: OnFailure