Kubernetes Fundamentals
kubectl — The CLI
\\\`bash
Context management
kubectl config get-contexts # List clusters/contexts
kubectl config use-context prod # Switch cluster
kubectl config current-context # Show current
Get resources
kubectl get pods # Pods in default namespace
kubectl get pods -n kube-system # Specific namespace
kubectl get pods -A # All namespaces
kubectl get pods -o wide # Show node and IP
kubectl get pods -o yaml # Full YAML output
kubectl get all # All common resources
kubectl get nodes # Cluster nodes
Describe (events, details)
kubectl describe pod mypod
kubectl describe node node01
kubectl describe deployment myapp
Logs
kubectl logs mypod # Pod logs
kubectl logs mypod -c container # Specific container
kubectl logs -f mypod # Follow
kubectl logs --previous mypod # Previous crashed container
Execute
kubectl exec -it mypod -- bash # Shell into pod
kubectl exec mypod -- cat /etc/hosts # Run command
Apply and delete
kubectl apply -f manifest.yaml # Create/update from file
kubectl delete -f manifest.yaml # Delete from file
kubectl delete pod mypod # Delete by name
kubectl delete pod mypod --grace-period=0 # Force delete
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Pod Manifest
\\\`yaml
apiVersion: v1
kind: Pod
metadata:
name: myapp
namespace: production
labels:
app: myapp
version: "1.0"
spec:
containers:
- name: myapp
image: myapp:1.0
ports:
- containerPort: 3000
# Resource limits (ALWAYS set these!)
resources:
requests:
memory: "128Mi"
cpu: "100m" # 100 millicores = 0.1 CPU
limits:
memory: "256Mi"
cpu: "500m"
# Environment variables
env:
- name: DB_HOST
value: "postgres-service"
- name: DB_PASSWORD
valueFrom:
secretKeyRef:
name: db-secret
key: password
# Health checks (critical for production)
livenessProbe:
httpGet:
path: /health
port: 3000
initialDelaySeconds: 30
periodSeconds: 10
failureThreshold: 3
readinessProbe:
httpGet:
path: /ready
port: 3000
initialDelaySeconds: 5
periodSeconds: 5
\\\`
Deployment
\\\`yaml
apiVersion: apps/v1
kind: Deployment
metadata:
name: myapp
namespace: production
spec:
replicas: 3
selector:
matchLabels:
app: myapp
# Rolling update strategy
strategy:
type: RollingUpdate
rollingUpdate:
maxSurge: 1 # Max pods above desired during update
maxUnavailable: 0 # No downtime (always 3 running)
template:
metadata:
labels:
app: myapp
spec:
containers:
- name: myapp
image: myapp:1.0
resources:
requests:
memory: "128Mi"
cpu: "100m"
limits:
memory: "256Mi"
cpu: "500m"
\\\`
\\\`bash
Deployment operations
kubectl rollout status deployment/myapp # Watch rollout progress
kubectl rollout history deployment/myapp # Rollout history
kubectl rollout undo deployment/myapp # Rollback
kubectl rollout undo deployment/myapp --to-revision=2
kubectl scale deployment myapp --replicas=5
kubectl set image deployment/myapp myapp=myapp:2.0 # Update image
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Services
\\\`yaml
ClusterIP - internal only (default)
apiVersion: v1
kind: Service
metadata:
name: myapp-service
spec:
selector:
app: myapp # Routes to pods with this label
ports:
- port: 80 # Service port
targetPort: 3000 # Container port
type: ClusterIP
LoadBalancer - external access (creates cloud load balancer)
apiVersion: v1
kind: Service
metadata:
name: myapp-lb
spec:
selector:
app: myapp
ports:
- port: 80
targetPort: 3000
type: LoadBalancer
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ConfigMaps and Secrets
\\\`bash
Create ConfigMap
kubectl create configmap app-config \
--from-literal=LOG_LEVEL=info \
--from-literal=MAX_CONNECTIONS=100
Create Secret
kubectl create secret generic db-secret \
--from-literal=username=admin \
--from-literal=password=s3cr3t
View (secrets are base64 encoded)
kubectl get secret db-secret -o jsonpath='{.data.password}' | base64 -d
\\\`
\\\`yaml
Use in Pod
spec:
containers:
- name: app
envFrom:
- configMapRef:
name: app-config # All keys as env vars
volumeMounts:
- name: config-volume
mountPath: /etc/config
volumes:
- name: config-volume
configMap:
name: app-config
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