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Chapter 3.2 - YAML Declaration for Pods

Learning Objectives​

By the end of this chapter, you will be able to:

  • Understand the YAML structure of a Pod
  • Create Pods with kubectl
  • Define resources (CPU, memory)
  • Configure environment variables
  • Mount volumes

YAML Structure of a Pod​

Basic Structure​

apiVersion: v1
kind: Pod
metadata:
  name: my-pod
  labels:
    app: my-app
    env: production
spec:
  containers:
  - name: my-container
    image: nginx:1.20
    ports:
    - containerPort: 80

Main Sections​

  1. apiVersion: Kubernetes API version
  2. kind: Resource type (Pod)
  3. metadata: Metadata (name, labels, annotations)
  4. spec: Pod specification

Complete Example​

apiVersion: v1
kind: Pod
metadata:
  name: web-server
  namespace: default
  labels:
    app: web
    tier: frontend
    version: v1
spec:
  containers:
  - name: nginx
    image: nginx:1.20
    imagePullPolicy: IfNotPresent
    ports:
    - name: http
      containerPort: 80
      protocol: TCP
    env:
    - name: ENV_VAR
      value: "production"
    resources:
      requests:
        cpu: "100m"
        memory: "128Mi"
      limits:
        cpu: "500m"
        memory: "512Mi"
    volumeMounts:
    - name: config
      mountPath: /etc/nginx/conf.d
  volumes:
  - name: config
    configMap:
      name: nginx-config
  restartPolicy: Always

Resources (CPU and Memory)​

Requests and Limits​

resources:
  requests:    # Guaranteed resources
    cpu: "100m"      # 0.1 CPU core
    memory: "128Mi"  # 128 Mebibytes
  limits:      # Maximum resources
    cpu: "500m"      # 0.5 CPU core
    memory: "512Mi"  # 512 Mebibytes

CPU Units:

  • 100m = 0.1 CPU
  • 1 = 1 CPU core
  • 2.5 = 2.5 CPU cores

Memory Units:

  • 128Mi = 128 Mebibytes
  • 1Gi = 1 Gibibyte
  • 500M = 500 Megabytes

Environment Variables​

Method 1: Direct​

env:
- name: DATABASE_URL
  value: "postgresql://localhost:5432/mydb"
- name: LOG_LEVEL
  value: "info"

Method 2: From ConfigMap​

env:
- name: CONFIG_VALUE
  valueFrom:
    configMapKeyRef:
      name: my-config
      key: config-key

Method 3: From Secret​

env:
- name: PASSWORD
  valueFrom:
    secretKeyRef:
      name: my-secret
      key: password

Volumes​

Volume Types​

volumes:
# Volume from ConfigMap
- name: config
  configMap:
    name: my-config

# Volume from Secret
- name: secrets
  secret:
    secretName: my-secret

# Temporary volume
- name: temp
  emptyDir: {}

# Persistent volume
- name: data
  persistentVolumeClaim:
    claimName: my-pvc

Mounting in the Container​

volumeMounts:
- name: config
  mountPath: /etc/config
  readOnly: true

kubectl Commands​

Create a Pod​

# From a YAML file
kubectl apply -f pod.yaml

# From the command line
kubectl run my-pod --image=nginx:1.20

# Create and display the YAML
kubectl run my-pod --image=nginx:1.20 --dry-run=client -o yaml > pod.yaml

Manage Pods​

# List Pods
kubectl get pods

# View details
kubectl describe pod my-pod

# View logs
kubectl logs my-pod

# Execute a command
kubectl exec -it my-pod -- /bin/bash

# Delete a Pod
kubectl delete pod my-pod

Summary​

In this chapter, you learned:

YAML Structure: apiVersion, kind, metadata, spec
Resources: Requests (guaranteed) and Limits (maximum)
Environment Variables: Direct, ConfigMap, Secret
Volumes: ConfigMap, Secret, emptyDir, PVC
Commands: kubectl apply, get, describe, logs, exec, delete

Next Steps​

Now that you know how to create Pods:

Chapter 3.3: Labels and Selectors
Lab 3.1: Creating and Managing Pods

Chapter created: December 2024