• Kubernetes doesn’t run containers directly on the nodes. Every container is encapsulated by a pod.
• Smallest unit of Kubernetes
• A pod is a single instance of an application. If another instance of the application needs to be deployed, another pod is deployed with the containerized application running inside it.
• Creates a running environment over the container so that we only interact with the Kubernetes layer. This allows us to replace the container technology like Docker.
• Each pod gets an internal IP address for communicating with each other (virtual network created by K8)
• If a pod is restarted (maybe after the application running on it crashed), its IP address may change

<aside> ⛔

Sometimes we need to have a helper container for the application container. In that case, we can run both containers inside the same pod. This way both containers share the same storage and network and can reference each other as localhost

Without using Pods, making a setup like this would be difficult as we need to manage attaching the helper containers to the application containers and kill them if the application container goes down.

Although, most use cases of pods revolve around single containers, it provides flexibility to add a helper container in the future as the application evolves.

</aside>

Config file for a Pod

apiVersion: v1
kind: Pod
metadata:
  labels:
    name: frontend
spec:
  containers:
	  - name: httpd
	    image: httpd:2.4-alpine

Restart Policy

The default behavior of K8s is to restart a pod if it terminates. This is desirable for long running containers like web applications or databases. But, this is not desirable for short-lived containers such as a container to process an image or run analytics.

restartPolicy allows us to specify when K8s should restart the pod.

• Always - restart the pod if it goes down (default)
• Never - never restart the pod
• OnFailure - restart the pod only if the container inside failed (returned non zero exit code after execution)

apiVersion: v1
kind: Pod
metadata:
  labels:
    name: analytics
spec:
  containers:
	  - name: analytics
	    image: analytics
	restartPolicy: Never