Kubernetes and OpenShift Quick Reference and Cheat Sheets¶

Essential kubectl Commands¶

Cluster Information¶

kubectl cluster-info                    # Display cluster info
kubectl version                         # Show client and server versions
kubectl get nodes                       # List all nodes
kubectl get nodes -o wide              # List nodes with more details
kubectl describe node <node-name>      # Detailed node information
kubectl top nodes                      # Show node resource usage

Working with Pods¶

# List pods
kubectl get pods                       # Pods in current namespace
kubectl get pods -A                    # All namespaces
kubectl get pods -n <namespace>        # Specific namespace
kubectl get pods -o wide              # More details (node, IP)
kubectl get pods --show-labels        # Show labels
kubectl get pods -l app=nginx         # Filter by label

# Describe and logs
kubectl describe pod <pod-name>        # Detailed pod info
kubectl logs <pod-name>               # View logs
kubectl logs <pod-name> -f            # Follow logs
kubectl logs <pod-name> --previous    # Previous container logs
kubectl logs <pod-name> -c <container> # Specific container

# Execute commands
kubectl exec <pod-name> -- <command>   # Run command
kubectl exec -it <pod-name> -- bash    # Interactive shell

# Port forwarding
kubectl port-forward <pod-name> 8080:80

# Copy files
kubectl cp <pod-name>:/path/file ./local-file
kubectl cp ./local-file <pod-name>:/path/file

# Delete pods
kubectl delete pod <pod-name>
kubectl delete pods --all
kubectl delete pods -l app=nginx

Deployments¶

# Create deployment
kubectl create deployment nginx --image=nginx:1.21
kubectl create deployment nginx --image=nginx:1.21 --replicas=3

# List deployments
kubectl get deployments
kubectl get deploy -o wide

# Scale deployment
kubectl scale deployment nginx --replicas=5

# Update image
kubectl set image deployment/nginx nginx=nginx:1.22

# Rollout management
kubectl rollout status deployment/nginx
kubectl rollout history deployment/nginx
kubectl rollout undo deployment/nginx
kubectl rollout restart deployment/nginx

# Edit deployment
kubectl edit deployment nginx

# Delete deployment
kubectl delete deployment nginx

Services¶

# Create service
kubectl expose deployment nginx --port=80 --type=LoadBalancer
kubectl create service clusterip nginx --tcp=80:80

# List services
kubectl get services
kubectl get svc -o wide

# Describe service
kubectl describe svc nginx

# Delete service
kubectl delete svc nginx

ConfigMaps and Secrets¶

# ConfigMaps
kubectl create configmap app-config --from-literal=key=value
kubectl create configmap app-config --from-file=config.properties
kubectl get configmaps
kubectl describe configmap app-config
kubectl delete configmap app-config

# Secrets
kubectl create secret generic db-secret --from-literal=password=secret123
kubectl create secret docker-registry regcred --docker-server=docker.io --docker-username=user --docker-password=pass
kubectl get secrets
kubectl describe secret db-secret
kubectl delete secret db-secret

Namespaces¶

kubectl get namespaces
kubectl create namespace dev
kubectl delete namespace dev
kubectl config set-context --current --namespace=dev

Resource Management¶

# Set resources
kubectl set resources deployment nginx --limits=cpu=500m,memory=512Mi --requests=cpu=250m,memory=256Mi

# Autoscaling
kubectl autoscale deployment nginx --min=2 --max=10 --cpu-percent=70
kubectl get hpa

# Resource quotas
kubectl create quota compute-quota --hard=cpu=10,memory=20Gi,pods=50
kubectl get resourcequota

Debugging¶

# Events
kubectl get events
kubectl get events --sort-by=.metadata.creationTimestamp
kubectl get events -w

# Debug pod
kubectl run debug --rm -it --image=busybox -- sh
kubectl debug <pod-name> -it --image=busybox

# Resource usage
kubectl top pods
kubectl top nodes
kubectl top pods --sort-by=memory

Apply and Delete¶

kubectl apply -f deployment.yaml
kubectl apply -f directory/
kubectl apply -f https://example.com/deployment.yaml
kubectl delete -f deployment.yaml
kubectl delete all --all

OpenShift (oc) Commands¶

Basic Commands¶

oc login https://api.cluster.example.com:6443
oc whoami
oc status
oc projects
oc project myapp
oc new-project myapp

Application Management¶

# Create app
oc new-app nodejs:16~https://github.com/myorg/myapp.git
oc new-app --docker-image=nginx:latest

# Expose service
oc expose service myapp

# Build operations
oc start-build myapp
oc logs -f bc/myapp
oc get builds

# Routes
oc get routes
oc create route edge myapp --service=myapp

Security¶

# SCC management
oc get scc
oc adm policy add-scc-to-user anyuid -z myapp-sa
oc describe pod myapp | grep scc

# RBAC
oc adm policy add-role-to-user admin user1 -n myapp
oc adm policy add-cluster-role-to-user cluster-admin user1

YAML Templates¶

Pod¶

apiVersion: v1
kind: Pod
metadata:
  name: myapp
  labels:
    app: myapp
spec:
  containers:
    - name: myapp
      image: myapp:1.0
      ports:
        - containerPort: 8080
      env:
        - name: ENV_VAR
          value: "value"
      resources:
        requests:
          memory: "256Mi"
          cpu: "250m"
        limits:
          memory: "512Mi"
          cpu: "500m"
      livenessProbe:
        httpGet:
          path: /health
          port: 8080
        initialDelaySeconds: 30
        periodSeconds: 10
      readinessProbe:
        httpGet:
          path: /ready
          port: 8080
        initialDelaySeconds: 5
        periodSeconds: 5

Deployment¶

apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
spec:
  replicas: 3
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
        - name: myapp
          image: myapp:1.0
          ports:
            - containerPort: 8080

Service¶

apiVersion: v1
kind: Service
metadata:
  name: myapp-service
spec:
  selector:
    app: myapp
  ports:
    - protocol: TCP
      port: 80
      targetPort: 8080
  type: LoadBalancer

ConfigMap¶

apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  database_url: "postgres://db:5432"
  log_level: "info"

Secret¶

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

Ingress¶

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: myapp-ingress
  annotations:
    nginx.ingress.kubernetes.io/rewrite-target: /
spec:
  ingressClassName: nginx
  rules:
    - host: myapp.example.com
      http:
        paths:
          - path: /
            pathType: Prefix
            backend:
              service:
                name: myapp-service
                port:
                  number: 80

PersistentVolumeClaim¶

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: myapp-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 10Gi
  storageClassName: standard

HorizontalPodAutoscaler¶

apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  name: myapp-hpa
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: myapp
  minReplicas: 2
  maxReplicas: 10
  metrics:
    - type: Resource
      resource:
        name: cpu
        target:
          type: Utilization
          averageUtilization: 70

Common Troubleshooting Scenarios¶

Pod Won't Start¶

# Check status
kubectl get pods
kubectl describe pod <pod-name>

# Common issues:
# - ImagePullBackOff: Check image name, registry credentials
# - CrashLoopBackOff: Check logs, application errors
# - Pending: Check resources, node availability
# - Error: Check configuration, permissions

Service Not Accessible¶

# Check service and endpoints
kubectl get svc
kubectl get endpoints

# Test connectivity
kubectl run test --rm -it --image=busybox -- wget -O- http://service-name

# Check network policies
kubectl get networkpolicy

High Resource Usage¶

# Check usage
kubectl top nodes
kubectl top pods

# Check limits
kubectl describe pod <pod-name> | grep -A 5 Limits

# Scale or adjust resources
kubectl scale deployment myapp --replicas=5
kubectl set resources deployment myapp --limits=cpu=1,memory=1Gi

Resource Units¶

CPU¶

1 CPU = 1000m (millicores)
100m = 0.1 CPU
500m = 0.5 CPU
1 = 1 CPU core

Memory¶

Ki = Kibibyte (1024 bytes)
Mi = Mebibyte (1024 Ki)
Gi = Gibibyte (1024 Mi)
K = Kilobyte (1000 bytes)
M = Megabyte (1000 K)
G = Gigabyte (1000 M)

Port Numbers¶

Kubernetes Components¶

API Server: 6443
etcd: 2379-2380
Kubelet: 10250
kube-scheduler: 10259
kube-controller-manager: 10257

Common Services¶

HTTP: 80
HTTPS: 443
NodePort range: 30000-32767
PostgreSQL: 5432
MySQL: 3306
MongoDB: 27017
Redis: 6379

Label Selectors¶

Equality-based¶

kubectl get pods -l app=nginx
kubectl get pods -l app=nginx,tier=frontend
kubectl get pods -l 'app!=nginx'

Set-based¶

kubectl get pods -l 'env in (prod,staging)'
kubectl get pods -l 'tier notin (frontend,backend)'
kubectl get pods -l 'app,!tier'

JSONPath Examples¶

# Get pod IPs
kubectl get pods -o jsonpath='{.items[*].status.podIP}'

# Get node names
kubectl get nodes -o jsonpath='{.items[*].metadata.name}'

# Get container images
kubectl get pods -o jsonpath='{.items[*].spec.containers[*].image}'

# Get resource requests
kubectl get pods -o jsonpath='{.items[*].spec.containers[*].resources.requests}'

# Custom columns
kubectl get pods -o custom-columns=NAME:.metadata.name,STATUS:.status.phase,IP:.status.podIP

Useful Aliases¶

# Add to ~/.bashrc or ~/.zshrc
alias k='kubectl'
alias kgp='kubectl get pods'
alias kgs='kubectl get svc'
alias kgd='kubectl get deployments'
alias kd='kubectl describe'
alias kl='kubectl logs'
alias kx='kubectl exec -it'
alias ka='kubectl apply -f'
alias kdel='kubectl delete'

# OpenShift
alias o='oc'
alias ogp='oc get pods'
alias ol='oc logs'

Environment Variables¶

Common Kubernetes Variables¶

KUBECONFIG=~/.kube/config
KUBERNETES_SERVICE_HOST=kubernetes.default.svc
KUBERNETES_SERVICE_PORT=443

Useful in Scripts¶

NAMESPACE=${NAMESPACE:-default}
DEPLOYMENT_NAME=${DEPLOYMENT_NAME:-myapp}
IMAGE=${IMAGE:-myapp:latest}
REPLICAS=${REPLICAS:-3}

Exit Codes¶

0: Success
1: General error
2: Misuse of shell command
126: Command cannot execute
127: Command not found
130: Terminated by Ctrl+C
137: Killed (SIGKILL) - often OOM
143: Terminated (SIGTERM)

Pod Lifecycle Phases¶

Pending: Accepted but not scheduled
Running: Bound to node, containers running
Succeeded: All containers terminated successfully
Failed: At least one container failed
Unknown: Cannot determine state

Container States¶

Waiting: Not running yet
Running: Executing without issues
Terminated: Finished execution or failed

Service Types¶

ClusterIP: Internal cluster access (default)
NodePort: Exposes on each node's IP
LoadBalancer: Cloud provider load balancer
ExternalName: Maps to DNS name

Storage Access Modes¶

ReadWriteOnce (RWO): Single node read-write
ReadOnlyMany (ROX): Multiple nodes read-only
ReadWriteMany (RWX): Multiple nodes read-write

Deployment Strategies¶

Rolling Update¶

strategy:
  type: RollingUpdate
  rollingUpdate:
    maxSurge: 1
    maxUnavailable: 0

Recreate¶

strategy:
  type: Recreate

Network Policy Types¶

Ingress: Incoming traffic to pods
Egress: Outgoing traffic from pods

RBAC Resources¶

Role: Namespace-scoped permissions
ClusterRole: Cluster-wide permissions
RoleBinding: Binds Role to subjects
ClusterRoleBinding: Binds ClusterRole to subjects

Common Annotations¶

annotations:
  kubernetes.io/change-cause: "Update to version 2.0"
  prometheus.io/scrape: "true"
  prometheus.io/port: "9090"
  nginx.ingress.kubernetes.io/rewrite-target: /

Useful One-Liners¶

# Delete all evicted pods
kubectl get pods --all-namespaces -o json | jq -r '.items[] | select(.status.reason=="Evicted") | "kubectl delete pod \(.metadata.name) -n \(.metadata.namespace)"' | sh

# Get pods sorted by restart count
kubectl get pods --sort-by='.status.containerStatuses[0].restartCount'

# Get pods not running
kubectl get pods --field-selector=status.phase!=Running

# Get pod resource usage
kubectl top pods --sort-by=memory

# Watch pod status
watch kubectl get pods

# Get all images used in cluster
kubectl get pods --all-namespaces -o jsonpath="{.items[*].spec.containers[*].image}" | tr -s '[[:space:]]' '\n' | sort | uniq

# Count pods per node
kubectl get pods --all-namespaces -o json | jq '.items | group_by(.spec.nodeName) | map({node: .[0].spec.nodeName, count: length})'

Key Concepts to Remember¶

Kubernetes Architecture¶

Control Plane: API Server, etcd, Scheduler, Controller Manager
Node: kubelet, kube-proxy, Container Runtime
Add-ons: DNS, Dashboard, Monitoring

Core Objects¶

Pod: Smallest deployable unit
Deployment: Manages ReplicaSets
Service: Network abstraction
ConfigMap/Secret: Configuration management
Volume: Storage abstraction

Networking¶

Every pod gets its own IP
Pods can communicate without NAT
Services provide stable endpoints
Ingress manages external access

Security¶

RBAC for access control
Network Policies for traffic control
Pod Security Standards
Secrets for sensitive data

Best Practices¶

Set resource requests and limits
Use health checks
Implement monitoring and logging
Follow GitOps principles
Document everything
Test in non-production first