Kubernetes Foundation

Important Concepts

Pods

Smallest deployable unit in kubernetes.

# pod-example.yaml
apiVersion: v1
kind: Pod
metadata:
  name: nginx-pod
  labels:
    app: nginx
spec:
  containers:
  - name: nginx
    image: nginx:latest
    ports:
    - containerPort: 80

Services

Enables communication between Pods

# service-example.yaml
apiVersion: v1
kind: Service
metadata:
  name: nginx-service
spec:
  selector:
    app: nginx
  ports:
  - protocol: TCP
    port: 80
    targetPort: 80
  type: ClusterIP

Deployments

Manages the replication and updates of the pods

# deployment-example.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:latest
        ports:
        - containerPort: 80

ConfigMaps

Saves the Configuration data

# configmap-example.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  database_url: "postgresql://localhost:5432/mydb"
  debug: "true"

Secrets

Saves the sensible data, like passwords

# secret-example.yaml
apiVersion: v1
kind: Secret
metadata:
  name: app-secret
type: Opaque
data:
  username: YWRtaW4=  # base64 encoded "admin"
  password: MWYyZDFlMmU2N2Rm  # base64 encoded "1f2d1e2e67df"

Working with YAML Files

Generating ConfigMap YAML

Use the --dry-run=client flag combined with -o yaml to generate the YAML manifest without applying it, then redirect (>) it to a file:

kubectl create configmap app-config --from-literal=ENV=production --dry-run=client -o yaml > app-config.yaml

Generating Secret YAML

Use:

kubectl create secret generic app-secret --from-literal=password=supersecret --dry-run=client -o yaml > app-secret.yaml

# This will generate the secret manifest as YAML and save it to `app-secret.yaml`.
    
# You can then apply it anytime with:
kubectl apply -f app-secret.yaml

Applying Multiple Files

You have a few options:

1. Apply files one by one:

kubectl apply -f app-secret.yaml
kubectl apply -f app-config.yaml

2. Apply a directory containing both files:

If both files are in the same folder, say /home/j551n/Docs, just run:

kubectl apply -f /home/j551n/Docs/

That applies all manifests inside the folder.

3. Use multiple `-f` flags (supported in newer versions):

kubectl apply -f app-secret.yaml -f app-config.yaml

What's Next?

Now that you understand Kubernetes fundamentals, here's your learning path:

AWX Deployment

Deploy AWX automation platform on K3s

Docker Basics

Learn containerization before advanced K8s

Proxmox Setup

Set up your virtualization foundation

Recommended Timeline

Next Step: Deploy AWX on K3s - Put your knowledge into practice
Then: Explore more Kubernetes applications and services
Finally: Set up monitoring and logging for your cluster

Prerequisites Check

✅ Understand Pods, Services, Deployments
⏳ Next: Learn AWX deployment process
⏳ Later: Advanced Kubernetes networking

Kubernetes Fundamentals