DevOps Classroomnotes 27/Nov/2022

Kubernetes (k8s)

K8s is a container orchcestration software.
One of major properties of k8s is
- self healing
K8s is distributed application which is called as k8s cluster
Actual k8s
k8s was developed by Google with the experience of running containers. Google has inhouse products called as omega and borg
k8s has its dna. K8s was donated as a open source project to CNCF
K8s is designed to work with any container technology.
K8s is cluster so we interact with master nodes. There are two ways of interacting, where as for k8s it exposes APIs
- From code/restapi with json
- From command line where k8s gives a cmd line tools kubectl
In kubectl can be interacted in two ways
- imperative commands
- declarative (yaml)
To k8s we always express the desired state (What is that we want)
These yaml files where we describe our desired state are called as manifests.

K8s at the node level has two types of nodes
- master nodes
- node
Master node has 4 components and one additional component for cloud based k8s service
- API Server:
  - This is way to interact with k8s cluster
  - This is responsible for all the communications in k8s cluster
- etcd:
  - This is memory of k8s cluster
- Scheduler: Looks out for any new work and it does
- Controller: This ensures desired state is maintained
- Cloud Controller: This is component in k8s with cloud specific knowledge
Nodes have the following components
- Container runtime: This is technology in which your container is created (docker, rkt, containerd)
- kube-proxy: is responsible for networking
- kubelet: Agent that runs on nodes waiting for instructions from master and execute them.