Concepts

History¶

Kubernetes also called k8s (a "k" followed by 8 chars and a "s") or simply kube means "Helmsman" in Greek. It is a container orchestrator inspired by Google Borg System which were orchestrating billions of containers on Google infrastructure.

Version v1.0.0 of Kubernetes was released in July 2015, the last version as of today (October 2024) is v1.31.1. The release cycle is quite fast with 3 minor releases per year.

Main functionalities¶

Kubernetes is a container orchestrator offering main functionalities, such as:

Management of applications running in containers
Self-healing
Service discovery
Usage of Secrets and Configurations
Long-running process and batch jobs
Role Based Access Control (RBAC)
Storage Orchestration

Manages applications in production¶

environments

Major project in the open-source ecosystem¶

Kubernetes is the first graduated project within the CNCF, it was followed by major players like etcd and Prometheus

CNCF

What is a Kubernetes cluster made of ?¶

A Kubernetes cluster is composed of nodes, where a node is either a virtual machine or a bare metal server. A node can belong to the Control Plane which run processes in charge of managing the cluster and the applications running on it. Or, a node can be a Worker dedicated to run Pods, a group of containers sharing a network stack and storage.

cluster

How to access a cluster¶

A cluster usually comes with a kubeconfig file which contains all the information to communicate with the cluster API Server. This file can be used to configure the standard kubectl binary to manage the cluster. The kubeconfig file can also be used with tools like k9s, Mirantis Lens, ... which give a higher level view of the cluster.

access

Various workload resources for different use cases¶

To run a Pod we often rely on a higher level resource, instead of running it directly. The workload resources are:

Deployment : web server
DaemonSet : one agent per node
Job / CronJob : batch
StatefulSet : stateful application

workload resources

A request that reaches a Service is load-balanced between the exposed Pods

service

A Pod can use several resources

ConfigMap : contains configuration data
Secret : contains sensitive data
PersistentVolumeClaim / PersistentVolume : storage management

pod resources

Several types of resources¶

Summary

An application runs in a Namespace¶

Namespace

Resource creation¶

Definition of a YAML specification
Usage of the kubectl binary to send the spec to the API Server

www.yaml

apiVersion: v1
kind: Pod
metadata:
  name: www
spec:
  containers:
  - name: www
    image: nginx:1.24

kubectl apply -f www.yaml