Nodes

Nodes serve as working machine in a k8s cluster. A node can be a physical computer or virtual machine.

Node Requirements

They are simplest unit that you can interact with.
Smallest deployable unit
You can create, deploy and delete pods, and it represents one running process on your cluster.
It is one single unit of deployment.
They never self heal and not restarted by scheduler. Do not interact with Pods directly.
They contain the following:
- Docker application container
- storage resources
- unique network IP
- options how container should run

Pending: container not created yet
Running
Succeeded: All containers in the pod exited with status 0
Failed: At least one container exited with non zero status
CrashLoopBackOff: Container fails to start and Kubernetes tries to start it again and again.

Pods are abstraction for containers.
Each pods has unique IP accessible via other pods.
When a container starts we need to bind the application port to the host port, since keeping track of available ports becomes difficult, pods solve this problem.
A single pod can have more than one container running on it but one of them must be main container.
At max you can have 6 containers (verify it!). Generally we keep single container
we can have one main and other helper container for eg. scheduler, authentication etc.
There is “pause” (aka “sandbox”) container for each pod which reserves and holds network namespace and helps in communication between containers

Since a pod is ephemeral and can die easily, hence its IP address can change easily. Service attaches a permanent IP to the pod.