Pod definition in YAML in Kubernetes - Commands & Configuration

Introduction

A Pod is the smallest unit that runs one or more containers in Kubernetes. Defining a Pod in YAML lets you tell Kubernetes exactly what containers to run and how to run them.

When you want to run a single container or a tightly coupled group of containers together on the same machine.

When you need to test a simple application or service quickly without creating a full deployment.

When you want to specify container images, ports, and environment variables for your app in a clear file.

When you want to manually control the lifecycle of a container without automatic scaling.

When you want to learn Kubernetes basics by creating and managing Pods directly.

Config File - pod.yaml

pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: example-pod
  labels:
    app: example
spec:
  containers:
  - name: example-container
    image: nginx:1.23.3
    ports:
    - containerPort: 80

apiVersion: Specifies the Kubernetes API version to use.

kind: Defines the resource type, here it is a Pod.

metadata: Contains the Pod's name and labels for identification.

spec: Describes the desired state, including containers to run.

containers: Lists container details like name, image, and ports.

Commands

This command creates the Pod in Kubernetes using the pod.yaml file. It tells Kubernetes to start the container as defined.

Terminal

kubectl apply -f pod.yaml

Expected Output

pod/example-pod created

This command lists all Pods in the current namespace to check if the Pod is running.

Terminal

kubectl get pods

Expected Output

NAME          READY   STATUS    RESTARTS   AGE

example-pod   1/1     Running   0          10s

This command shows detailed information about the Pod, including container status, events, and resource usage.

Terminal

kubectl describe pod example-pod

Expected Output

Name:         example-pod

Namespace:    default

Priority:     0

Node:         <node-name>/192.168.1.10

Start Time:   Thu, 01 Jun 2023 12:00:00 +0000

Labels:       app=example

Status:       Running

IP:           10.244.1.5

Containers:

  example-container:

    Container ID:   docker://abcdef123456

    Image:          nginx:1.23.3

    Port:           80/TCP

    State:          Running

      Started:      Thu, 01 Jun 2023 12:00:05 +0000

Conditions:

  Type              Status

  Initialized       True 

  Ready             True 

  ContainersReady   True 

  PodScheduled      True 

Events:

  Type    Reason     Age   From               Message

  ----    ------     ----  ----               -------

  Normal  Scheduled  1m    default-scheduler  Successfully assigned default/example-pod to <node-name>

  Normal  Pulled     1m    kubelet            Container image "nginx:1.23.3" already present on machine

  Normal  Created    1m    kubelet            Created container example-container

  Normal  Started    1m    kubelet            Started container example-container

Key Concept

If you remember nothing else from this pattern, remember: a Pod YAML file tells Kubernetes exactly what containers to run and how to run them.

Common Mistakes

Forgetting to specify the container image in the YAML file.

Without an image, Kubernetes cannot start the container, so the Pod will fail to run.

Always include the 'image' field under each container in the spec section.

Using incorrect indentation or syntax in the YAML file.

YAML is sensitive to spaces; wrong indentation causes parsing errors and prevents Pod creation.

Use consistent two-space indentation and validate YAML syntax before applying.

Not checking Pod status after creation.

The Pod might fail to start or crash, and without checking status, you won't know the problem.

Run 'kubectl get pods' and 'kubectl describe pod <pod-name>' to verify Pod health.

Summary

Create a Pod by writing a YAML file that defines container details like image and ports.

Use 'kubectl apply -f pod.yaml' to create the Pod in Kubernetes.

Check Pod status with 'kubectl get pods' and get detailed info with 'kubectl describe pod example-pod'.