PODs

POD Definition

A pod definition file is used in Kubernetes to outline the pods and configuration involved in a deployment. Key configuration aspects to be defined within the pod definition file are:

Metadata	Define pod name, labels, and annotations for identification.
Containers	Specify the container's name, image, and pull policy.
Resource Allocation	Set requests (min resources) and limits (max resources) for CPU/memory.
Ports	Declare ports that the container exposes (e.g., containerPort: 80).
Environment Variables	Pass environment variables to the container.
Volume Mounts	Mount persistent volumes or config files to the container.
Volumes	Define storage (PersistentVolumeClaim, ConfigMap, or Secret).
Probes	Health checks using liveness and readiness probes.
Command/Args	Custom commands and arguments for container startup.
Affinity/Anti-Affinity	Rules for scheduling the pod on specific nodes.
Node Selector	Simple label-based node constraints for scheduling.
Security Context	Set user/group IDs, filesystem permissions, and privilege levels.
DNS Policy	Set pod-specific DNS settings (e.g., ClusterFirst).
Restart Policy	Control when to restart the pod (e.g., Always, OnFailure).

Create pods based on pod definition:

kubectl create -f pod-definition.yaml

Apply new changes to existing pods:

kubectl apply -f pod-definition.yaml

Example pod definition file

apiVersion: #v1 API version defined
kind: Pod #kind defined as pod
metadata: #begin metadata definitions
  name: nginx-pod
  labels:
    app: webapp
spec: #Begin pod specification
  containers: #Pod containers
  - name: nginx #Container name
    image: nginx:latest #Container image
    ports: #Port configuration
    - containerPort: 80