vknabel

Kubernetes Overview for Beginners

Posted on May 25, 2022

I have never done anything productive with Kubernetes before. But it is a really tough topic to get started with. It’s overwhelming.

Luckily I found an excellent Kubernetes tutorial on Youtube.

I made some personal notes while watching. Mostly to keep some overview for all the different concepts.

Today I haven’t finished the video, so the overview is only a rough draft. Some missing concepts are Storage Classes, Ingress Controllers and more!

Kubernetes Concepts

  • a Pod is an abstraction of usually one container.
  • all IP addresses are assigned and changed with every restart
  • Pods communicate using Services
  • External Services are accessible by IP and port
  • Ingress is used for external access using domains
  • A ConfigMap holds configuration data. Changing the config map prevents whole rebuilds and redeploys of specifc pods
  • Secrets are like ConfigMaps, but for sensitive data. Values are by default base64 encoded in the YAML.
  • Volumes connect storage (local or remote) to a Pod
  • Kubernetes does not handle storage!
  • LoadBalancers are a type of Services
  • Replicas are the amount of Deployments.
  • Deployments are blueprints for Pods

StatefulSets are like Deployments, but stateful.

  • They are designed to databases etc to avoid data inconsistency.
  • Harder to get right than a simple Deployment.
  • Databases are often deployed outside the cluster.

StatefulSet has volume claim templates, to create independent storage for each replica.

volumeClaimTemplates create a volume claim for each replica.

Kubernetes Architecture

Master nodes and worker nodes are kept separate to keep the cluster controllable. Imagine you couldn’t manage your cluster to increase the number of worker nodes or replicas.

Worker Nodes Runs multiple pods.

3 processes are running on each node:

  • container runtime
  • the Kubelet connects container runtime and the configuration
  • the kube proxy routes requests to services)

Master Nodes Manage the worker nodes.

Runs 4 processes:

  • Api Server / cluster gateway / authentication
  • the Scheduler that decides which worker node gets workload
  • Controller Manager observes the state of the cluster and makes changes
  • etcd is a Key-Value-Store for k8n