(Day 27) Task : Mastering Kubernetes: Writing YAML Manifests and Managing Pods :-

What is a Kubernetes YAML Manifest?

A Kubernetes YAML manifest is a configuration file that specifies the desired state of a Kubernetes resource, such as a pod or service, in a human-readable format. YAML (YAML Ain’t Markup Language) is indentation-sensitive (use 2 spaces, not tabs) and enables declarative resource management.

A YAML manifest typically includes four key fields:

• apiVersion: The Kubernetes API version (e.g., v1 for pods).

• kind: The resource type (e.g., Pod, Deployment).

• metadata: Information like name, namespace, and labels.

• spec: The desired configuration, such as containers or volumes.

Prerequisites

Ensure you have:

• A Kubernetes cluster (e.g., Minikube, Kind, or a cloud provider like GKE, EKS, or AKS).

• kubectl installed and configured to connect to your cluster.

• Basic familiarity with containers (e.g., Docker).

Install kubectl on Linux (adjust for your OS):

curl -LO "https://dl.k8s.io/release/$(curl -L -s https://dl.k8s.io/release/stable.txt)/bin/linux/amd64/kubectl"
chmod +x kubectl
sudo mv kubectl /usr/local/bin/

Verify installation:

kubectl version --client

Writing a Kubernetes YAML Manifest for a Pod :-

A pod is the smallest unit in Kubernetes, typically running one or more containers. Let’s create a YAML manifest for a pod named testpod running a Python HTTP server using the python:3.9-slim image.

Example: Python HTTP Server Pod YAML

apiVersion: v1
kind: Pod
metadata:
  name: testpod
  labels:
    app: python-http
spec:
  containers:
  - name: python-http-container
    image: python:3.9-slim
    command: ["python", "-m", "http.server", "8000"]
    ports:
    - containerPort: 8000

Explanation of the YAML

• apiVersion: v1: Uses the core Kubernetes API for pods.

• kind: Pod: Specifies we’re creating a pod.

• metadata: Sets the pod’s name (testpod) and a label (app: python-http) for identification.

• spec: Defines the pod’s configuration.

  • containers: Lists the containers in the pod.

    • name: The container’s name (python-http-container).

    • image: The Docker image (python:3.9-slim).

    • command: Runs Python’s built-in HTTP server on port 8000.

    • ports: Exposes port 8000 for the container.

Save this YAML as testpod.yaml.

Creating a Pod :-

To create the pod, run:

kubectl apply -f testpod.yaml

This command instructs Kubernetes to create or update the pod based on the YAML. Expected output:

pod/testpod created

Running and Verifying the Pod :-

Check the pod’s status:

kubectl get pods

Output:

NAME     READY   STATUS    RESTARTS   AGE
testpod  1/1     Running   0          12s

• READY: 1/1 means all containers are ready.

• STATUS: Running indicates the pod is operational.

• RESTARTS: Should be 0 for a healthy pod.

• AGE: Time since creation.

Viewing Pod Details :-

For detailed information:

kubectl describe pod testpod

This shows:

• Metadata (name, namespace, labels).

• Container details (image, command, ports).

• Events (e.g., pod scheduling, container startup).

Identifying the Node :-

To see which node hosts the pod:

kubectl get pods -o wide

Output:

NAME     READY   STATUS    RESTARTS   AGE   IP           NODE
testpod  1/1     Running   0          20s   10.244.0.3   minikube

The NODE column indicates the node (e.g., minikube).

Inspecting Pod Events and Logs :-

Viewing Pod Events :

Use kubectl describe pod testpod to see the “Events” section, which logs actions like:

• Pod scheduled to a node.

• Container image pulled.

• Container started or failed.

Example:

Events:
  Type    Reason     Age   From               Message
  ----    ------     ----  ----               -------
  Normal  Scheduled  25s   default-scheduler  Successfully assigned default/testpod to minikube
  Normal  Pulled     24s   kubelet            Container image "python:3.9-slim" already present
  Normal  Created    24s   kubelet            Created container python-http-container
  Normal  Started    24s   kubelet            Started container python-http-container

Viewing Container Logs

Check the container’s logs:

kubectl logs testpod

This shows the Python HTTP server’s output, such as access logs:

10.244.0.1 - - [10/Jun/2025 09:50:10] "GET / HTTP/1.1" 200 -

Getting Container Information

Inspect container details with:

kubectl describe pod testpod

The Containers section lists:

• Name: python-http-container.

• Image: python:3.9-slim.

• Command: python -m http.server 8000.

• Ports: 8000/TCP.

• State: E.g., Running.

• Environment Variables: None in this case.

For a structured view:

kubectl get pod testpod -o json

This outputs a JSON object with pod and container details.

Deleting a Pod :-

To delete the pod:

kubectl delete pod testpod

Output:

pod "testpod" deleted

Or delete using the YAML file:

kubectl delete -f testpod.yaml

If the pod is managed by a controller (e.g., Deployment), it may be recreated. Delete the controller to prevent this.