Kubernetes
The Operating System for the Cloud

What is Kubernetes (K8s)?

Kubernetes is an open-source system for the automation of deployment, scaling, and management of containerized applications. It makes running applications in the cloud easier, more reliable, and more scalable.

Advantages Container

Advantages Container managed by Kubernetes

Core Concepts

Interaction (simplified)

1. Application packaged in a Docker container.
2. Deployment created (defines desired state).
3. ReplicaSet ensures the correct number of Pods.
4. Pods run on Worker Nodes (which are part of a Node Pool).
5. Service makes Pods accessible (possibly via LoadBalancer or Ingress).

Important kubectl Commands

The following commands are essential for interacting with a Kubernetes cluster:

• kubectl get ...: List resources (e.g., Pods, Services, Deployments, Nodes, Namespaces, ConfigMaps, Secrets, PVs, PVCs).
  • Examples:
  • kubectl get pods
  • kubectl get services -n <namespace> (Resources in a specific namespace)
  • kubectl get nodes -o wide (More details)
• kubectl create ...: Create resources (e.g., Namespace, Deployment, Service).
  • Examples:
  • kubectl create namespace my-namespace
  • kubectl create deployment my-app --image=my-image (Simple Deployment)
• kubectl apply -f <file.yaml>: Create or update resources from a YAML file. This is the recommended way for most operations.
• kubectl delete ...: Delete resources (e.g., Pod, Deployment, Service, Namespace).
  • Examples:
    • kubectl delete pod my-pod -n my-namespace
    • kubectl delete -f my-deployment.yaml
• kubectl describe ...: Show detailed information about a resource (e.g., Pod, Service, Deployment, Node). Helpful for debugging.
  • Example: kubectl describe pod my-pod -n my-namespace
• kubectl logs ...: Display logs of a container in a Pod.
  • Examples:
  • kubectl logs my-pod (Logs of the default container)
  • kubectl logs my-pod -c my-container (Logs of a specific container)
  • kubectl logs -f my-pod (Follow logs live (stream))
• kubectl exec ...: Execute a command in a container of a Pod.
  • Examples:
  • kubectl exec -it my-pod -- /bin/bash (Interactive shell in the Pod)
  • kubectl exec my-pod -c my-container -- ls /app(Command in specific container)
• kubectl scale ...: Scale the number of replicas for a Deployment.
  • Example: kubectl scale deployment my-deployment --replicas=3
• kubectl rollout ...: Manage Deployment updates (e.g., status, history, undo).
  • Examples:
    • kubectl rollout status deployment/my-app
    • kubectl rollout history deployment/my-app
    • kubectl rollout undo deployment/my-app
• kubectl config ...: Manage kubectl configuration (e.g., contexts, clusters, users).
  • Examples:
    • kubectl config get-contexts
    • kubectl config use-context my-cluster-context
• kubectl expose ...: Create a Service for a Deployment or Pod to make it accessible.
  • Example: kubectl expose deployment my-deployment --type=LoadBalancer --port=80 --target-port=8080
• kubectl port-forward ...: Forward local ports to ports in a Pod. Useful for local debugging.
  • Example: kubectl port-forward my-pod 8080:80 (Forwards local port 8080 to port 80 in the Pod)

Basic Helm Commands

Helm is a package manager for Kubernetes that simplifies the deployment and management of applications. Here are some basic commands:

• helm repo add <name> <url>: Adds a Helm repository.
• helm repo update: Updates local information about available charts in the repositories.
• helm search repo <keyword>: Searches repositories for charts.
• helm install <release-name> <chart>: Installs a chart. A *release* is an instance of a chart running in a Kubernetes cluster.
• helm uninstall <release-name>: Uninstalls a release.
• helm list: Lists all releases.
• helm status <release-name>: Displays the status of a release.
• helm get values <release-name>: Displays the set values (values) of a release.
• helm show values <chart>: Displays the default values (default values) of a chart.
• helm get manifest <release-name> : Displays the generated Kubernetes manifest of a release.
• helm template <chart> > values.yaml: Outputs the rendered template of the values.yaml file without installing anything. Very useful for seeing the default values and creating a your own "values.yaml".
• helm upgrade <release-name> <chart>: Upgrades a release.