Detailed Concepts

Detailed Concepts

This segment consits of detailed bits about important concepts and components of kubernetes

Endpoints:

Endpoints track ip addresses of the pods assigned to the kubernetes service

kubectl get endpoint

Endpoint slices:

This breaks up end points into smaller manageble segments. Each slice has limit of 100 pods. Essential while solving scaling problems

Jobs:

A job creates one or more pods and will continue to retry execution of the pods until a specified number of them successfully terminate.

kubectl create job hello --image=busybox -- echo "Hello World"

Cron Jobs:

It is a job that executes based on repeating schedule.

kubectl create job hello --schedule="*\1 * * * *" --image=busybox -- echo "Hello World"

Selectors:

They are the way of selecting one or more kubernetes objects

1. Label selectors

2. Field selectors

3. Node selectors

K8s objects like services and replicasets will traget pods based on label selectors.

kubectl get pods --show-labels

Annotations:

Kubernetes annotations allow you to watch arbitory non-identifying metadata to objects. Often used by Ingress

RPC (Remote procedure call):

• It enables preogram to communicate with another program on a remote machine without knowing its remote.

• RPC is a framework of communication in distributed systems.

gRPC

💡 Think of this as method instead of REST or GraphQL

• gRPC is a modern open source high performance RPC.

• Kuberenetes uses gRPC for Pod communication

Kubelet:

• It is responsible for pod internal API communication via the API server.

• Node agent that runs on all nodes. Kubelet performs

  • Watchs pod changes

  • Configures container runtime

  • Pull images

  • Create Namespaces

  • Run containers

Kubectl:

• kubectl [command][TYPE][Name][Flags]

• Commands:

  • apply

  • get

  • log

  • describe

  • exec

• Type:

  • deploy

  • pods

  • ns

  • pc

  • pvc

  • secret

• Name:

  • case_sensitvie_name

• Flags:

  • different for each command

  • starts with --

Services:

Ip adresses of pods are ephemeral (temporary) hence we need services.

API Server:

• Exposes an HTTP API that lets end users, access different parts of your cluster and external components with one another.

• Let's you query & manipulate state of API objects in k8s

• Designed to scale horizontally.

Deployments:

Defalult deployment controller can be swapped out for other deployments tools eg: ArgoCD, Flux, Jenkins X

Replica Sets:

• ReplicaSet is a way to maintain a desired amount of redundant pods (replicas) to provide guraanteed availability.

• Horizontal pod autoscalar (HPA) can be used to autoscale a replicaset

Stateless:

• ReplicaSet is used for implementing

• Send request to any server, it doesn't matter

Stateful:

• StatefulSet is used for implementing

• Store session data in memory on VM

StatefulSet:

• A unique name and address is provided.

• Original index number assigned to each pod.

• Persistent volume is attached with a persistent link from pod to storage.

• StatefulSet will always start in the same order, and terminate in reverse order.