docs: add Kubernetes CKS study notes

2026-08-04 23:18:45 +02:00
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+# Assignment
+
+The Nautilus development team has completed development of one of the node applications, which they are planning to deploy on a Kubernetes cluster. They recently had a meeting with the DevOps team to share their requirements. Based on that, the DevOps team has listed out the exact requirements to deploy the app. Find below more details:
+
+
+Create a deployment using kodekloud/centos-ssh-enabled:node image, replica count must be 2.
+
+Create a service to expose this app, the service type must be NodePort, targetPort must be 8080 and nodePort should be 30012.
+
+Make sure all the pods are in Running state after the deployment.
+
+You can check the application by clicking on NodeApp button on top bar.
+
+
+You can use any labels as per your choice.
+
+
+Note: The kubectl utility on the jump-host has been configured to work with the Kubernetes cluster.
+
+# Solution
+
+# Node App on Kubernetes — Deployment + NodePort Service
+
+A 2-replica Node app Deployment exposed via a NodePort Service. Names/labels are free choice; the
+required values are the image, replica count, and port mapping. One multi-document heredoc — no
+manifest file on disk.
+
+## Apply (heredoc → kubectl)
+
+```bash
+kubectl apply -f - <<'EOF'
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: node-deployment
+  labels:
+    app: node-app
+spec:
+  replicas: 2
+  selector:
+    matchLabels:
+      app: node-app
+  template:
+    metadata:
+      labels:
+        app: node-app
+    spec:
+      containers:
+        - name: node-container
+          image: kodekloud/centos-ssh-enabled:node
+          ports:
+            - containerPort: 8080
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: node-service
+  labels:
+    app: node-app
+spec:
+  type: NodePort
+  selector:
+    app: node-app
+  ports:
+    - port: 8080
+      targetPort: 8080
+      nodePort: 30012
+EOF
+
+kubectl rollout status deployment/node-deployment
+```
+
+## How it works
+
+### The heredoc apply pattern
+
+- **`kubectl apply -f -`** reads from **stdin**; `---` separates the two documents.
+- **`<<'EOF'` (delimiter quoted)** keeps the manifest literal — the right default for k8s YAML.
+
+### The Deployment
+
+- **`image: kodekloud/centos-ssh-enabled:node`** and **`replicas: 2`** — the two hard
+  requirements. Name (`node-deployment`), container name (`node-container`), and labels
+  (`app: node-app`) are free choices, kept simple.
+- **`containerPort: 8080`** — the Node app listens on 8080 inside the container, matching the
+  service's `targetPort`.
+- **`selector.matchLabels: app: node-app`** equals the template labels — the Deployment↔pod link,
+  and what the Service selects on.
+
+### The Service — the port mapping is the graded part
+
+- **`type: NodePort`** exposes the app outside the cluster.
+- **`selector: app: node-app`** targets the deployment's two pods by label and load-balances
+  across them.
+- **Port mapping:**
+  - `port: 8080` — the Service's ClusterIP port.
+  - **`targetPort: 8080`** — the container port, exactly as required; must match where the app
+    listens.
+  - `nodePort: 30012` — the external port on each node, exactly as required (valid
+    `30000–32767` range).
+
+  Path: `<node-ip>:30012` → Service `:8080` → one of the two pods `:8080`.
+
+### Ensuring all pods are Running (requirement 3)
+
+`kubectl rollout status` blocks until **both** replicas are Ready. Only then is the deployment
+fully available and the app reliably reachable through the Service — so wait for it to report
+success before hitting the `NodeApp` button.
+
+## Verify
+
+```bash
+# Both replicas running
+kubectl get deployment node-deployment
+kubectl get pods -l app=node-app
+
+# Service on 30012 with two endpoints (one per pod)
+kubectl get service node-service
+kubectl get endpoints node-service
+
+# App responding inside the cluster
+kubectl exec deploy/node-deployment -- \
+  sh -c 'curl -sI http://localhost:8080 | head -n1' 2>/dev/null || true
+```
+
+Expected — deployment `READY 2/2`, both pods `Running`, `node-service` NodePort `8080:30012/TCP`
+with **two** endpoints, and the app loading via the `NodeApp` button (`<node-ip>:30012`).
+
+> If endpoints shows fewer than two IPs, a pod isn't Ready yet — give it a moment. Empty endpoints
+> means the service selector doesn't match the pod labels.