Kubernetes Operations¶

Prerequisites¶

• K3s installed and running
• kubectl available

Procedure: Apply a Manifest¶

When to use: Creating or updating Kubernetes resources (Pods, Deployments, Services).

Steps:

1. Apply a YAML file:

   kubectl apply -f manifest.yaml
   

2. Apply all files in a directory:

   kubectl apply -f ./k8s/
   

Troubleshooting:

• "The connection to the server was refused": Check if K3s/K8s is running (systemctl status k3s) or if KUBECONFIG is set.

Procedure: Check Pod Status¶

When to use: Monitoring deployment rollout and health.

Steps:

1. List all pods in default namespace:

   kubectl get pods
   

2. List pods in all namespaces:

   kubectl get pods -A
   

3. Watch for changes (live update):

   kubectl get pods -w
   

Troubleshooting:

• "ImagePullBackOff": Check image name and registry credentials. If using a local image, ensure imagePullPolicy is set to Never or IfNotPresent and the image exists on the node.
• "CrashLoopBackOff": Application is crashing. Check logs. Use kubectl logs <pod> --previous to see the logs of the last crashed instance.
• "Pending": The pod cannot be scheduled. Run kubectl describe pod <name> to check for resource limits (CPU/Memory) or Node Selectors/Taints.

Procedure: View Pod Logs¶

When to use: Debugging application errors.

Steps:

1. View logs:

   kubectl logs <pod_name>
   

2. View logs of a specific container (in multi-container pod):

   kubectl logs <pod_name> -c <container_name>
   

3. Follow logs:

   kubectl logs -f <pod_name>
   

Troubleshooting:

• "Pod not found": Check if you are in the correct namespace (-n <namespace>).

Procedure: Create a Namespace¶

When to use: Isolating resources for different environments or projects.

Steps:

1. Create namespace:

   kubectl create namespace my-app
   

2. Switch context to use it by default:

   kubectl config set-context --current --namespace=my-app
   

Troubleshooting:

• "Already exists": No action needed, or check spelling.

Procedure: Expose a Service via NodePort¶

When to use: Making an internal application accessible from outside the cluster.

Steps:

1. Expose a deployment:

   kubectl expose deployment my-dep --type=NodePort --port=80 --name=my-svc
   

2. Find the assigned NodePort:

   kubectl get svc my-svc
   

Troubleshooting:

• Cannot access port: Ensure firewall allows traffic on the assigned NodePort (30000-32767).

Procedure: Create an Ingress¶

When to use: Exposing HTTP/HTTPS services via a domain name.

Steps:

1. Create ingress.yaml:

   apiVersion: networking.k8s.io/v1
   kind: Ingress
   metadata:
     name: my-ingress
   spec:
     rules:
     - host: app.example.com
       http:
         paths:
         - path: /
           pathType: Prefix
           backend:
             service:
               name: my-svc
               port:
                 number: 80
   

2. Apply it:

   kubectl apply -f ingress.yaml
   

Troubleshooting:

• 404 Not Found: Ensure the Ingress Controller (Traefik/Nginx) is running and DNS points to the cluster IP.

Procedure: Debug a Failing Pod¶

When to use: Detailed investigation of why a pod is pending or failing.

Steps:

1. Describe the pod events and status:

   kubectl describe pod <pod_name>
   

   Look at the "Events" section at the bottom.

2. Exec into the pod (if running):

   kubectl exec -it <pod_name> -- /bin/sh
   

Troubleshooting:

• "SchedulingFailed": Insufficient CPU/Memory resources on nodes.

Quick Reference¶

Related Documentation¶

• Technologies: Kubernetes
• Concepts: Container Orchestration