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feat: Add Kubernetes basics guide and FAQ for Mycelium Cloud documentation

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# Kubernetes Basics
Essential Kubernetes concepts for deploying applications on Mycelium Cloud.
## What is Kubernetes?
Kubernetes (K8s) is a container orchestration platform that automates deploying, scaling, and managing containerized applications. Mycelium Cloud uses **K3s**, a lightweight Kubernetes distribution perfect for edge and cloud environments.
### Why Kubernetes?
- **Automated Deployment** - Deploy containers across multiple nodes
- **Self-Healing** - Automatically restart failed containers
- **Horizontal Scaling** - Scale applications up or down based on demand
- **Service Discovery** - Automatic DNS and load balancing
- **Rolling Updates** - Update applications with zero downtime
## Core Concepts
### Pods
A **Pod** is the smallest deployable unit in Kubernetes. It represents one or more containers that share:
- Network namespace (same IP address)
- Storage volumes
- Configuration
```yaml
apiVersion: v1
kind: Pod
metadata:
name: nginx-pod
spec:
containers:
- name: nginx
image: nginx:1.21
ports:
- containerPort: 80
```
```bash
# View pods
kubectl get pods
# View pod details
kubectl describe pod nginx-pod
# View pod logs
kubectl logs nginx-pod
```
### Deployments
A **Deployment** manages a replicated set of Pods and provides declarative updates.
Features:
- **Replica Management** - Maintain desired number of pods
- **Rolling Updates** - Update pods with zero downtime
- **Rollback** - Revert to previous versions
- **Self-Healing** - Replace failed pods automatically
```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:1.21
ports:
- containerPort: 80
```
```bash
# Create deployment
kubectl apply -f deployment.yaml
# View deployments
kubectl get deployments
# Scale deployment
kubectl scale deployment nginx-deployment --replicas=5
# Update image
kubectl set image deployment/nginx-deployment nginx=nginx:1.22
```
### Services
**Services** provide stable network endpoints for accessing pods.
#### ClusterIP (Default)
Internal-only service, accessible within the cluster:
```yaml
apiVersion: v1
kind: Service
metadata:
name: my-service
spec:
type: ClusterIP
selector:
app: nginx
ports:
- port: 80
targetPort: 80
```
#### NodePort
Exposes service on each node's IP at a static port:
```yaml
apiVersion: v1
kind: Service
metadata:
name: my-service
spec:
type: NodePort
selector:
app: nginx
ports:
- port: 80
targetPort: 80
nodePort: 30080 # 30000-32767
```
```bash
# View services
kubectl get services
# Describe service
kubectl describe service my-service
```
### Namespaces
**Namespaces** provide logical isolation for resources within a cluster.
```bash
# List namespaces
kubectl get namespaces
# Create namespace
kubectl create namespace my-app
# Use namespace
kubectl get pods -n my-app
```
## Storage
### Persistent Volumes
**PersistentVolumeClaim (PVC)** - Request for storage:
```yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: pvc-data
spec:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 10Gi
```
Use in pod:
```yaml
spec:
containers:
- name: app
image: myapp:latest
volumeMounts:
- name: data
mountPath: /data
volumes:
- name: data
persistentVolumeClaim:
claimName: pvc-data
```
## Configuration
### ConfigMaps
Store non-sensitive configuration data:
```yaml
apiVersion: v1
kind: ConfigMap
metadata:
name: app-config
data:
database_url: "postgres://db:5432/mydb"
log_level: "info"
```
```bash
# Create from literal
kubectl create configmap app-config --from-literal=key=value
# View configmaps
kubectl get configmaps
```
### Secrets
Store sensitive data (passwords, tokens, keys):
```yaml
apiVersion: v1
kind: Secret
metadata:
name: app-secret
type: Opaque
data:
password: cGFzc3dvcmQxMjM= # base64 encoded
```
```bash
# Create secret
kubectl create secret generic app-secret --from-literal=password=password123
# View secrets
kubectl get secrets
```
## Essential kubectl Commands
```bash
# Cluster info
kubectl cluster-info
kubectl get nodes
# Pods
kubectl get pods
kubectl get pods -o wide
kubectl describe pod <pod-name>
kubectl logs <pod-name>
kubectl logs -f <pod-name> # Follow logs
kubectl exec -it <pod-name> -- /bin/bash
# Deployments
kubectl get deployments
kubectl scale deployment <name> --replicas=5
kubectl rollout status deployment/<name>
kubectl rollout undo deployment/<name>
# Services
kubectl get services
kubectl describe service <service-name>
# Apply/Delete resources
kubectl apply -f file.yaml
kubectl delete -f file.yaml
# Port forwarding
kubectl port-forward pod/<pod-name> 8080:80
kubectl port-forward service/<service-name> 8080:80
# View all resources
kubectl get all --all-namespaces
# Check events
kubectl get events --sort-by=.metadata.creationTimestamp
```
## Labels and Selectors
**Labels** are key-value pairs attached to objects:
```yaml
metadata:
labels:
app: nginx
environment: production
tier: frontend
```
**Selectors** query objects by labels:
```bash
# Get pods with label
kubectl get pods -l app=nginx
# Get pods with multiple labels
kubectl get pods -l app=nginx,environment=production
```
## Best Practices
1. **Use Deployments** - Not bare pods, for self-healing and scaling
2. **Set Resource Limits** - Prevent resource exhaustion
```yaml
resources:
requests:
memory: "64Mi"
cpu: "250m"
limits:
memory: "128Mi"
cpu: "500m"
```
3. **Use Health Checks** - Implement liveness and readiness probes
4. **Use Namespaces** - Organize resources logically
5. **Version Control** - Store manifests in Git
6. **Use Labels** - Tag resources for organization
7. **Secrets Management** - Never hardcode sensitive data
## Next Steps
- **[Tutorial](/getstarted/mycelium-cloud/tutorial)** - Deploy real applications
- **[FAQ](/getstarted/mycelium-cloud/faq)** - Common questions and answers
## Additional Resources
- **Kubernetes Documentation**: [kubernetes.io/docs](https://kubernetes.io/docs/)
- **kubectl Cheat Sheet**: [kubernetes.io/docs/reference/kubectl/cheatsheet](https://kubernetes.io/docs/reference/kubectl/cheatsheet/)
- **K3s Documentation**: [docs.k3s.io](https://docs.k3s.io/)
---
:::tip Want to Learn More?
This covers the basics to get you started. For advanced topics like StatefulSets, DaemonSets, Ingress, and RBAC, check out the comprehensive Kubernetes documentation linked above.
:::