1. K3d Cluster Architecture

In a standard Docker setup, containers share the host's kernel and networking space directly. In Kubernetes, we introduce an abstraction layer: a Cluster. For this project, we use K3d, which packages K3s (a lightweight production-grade K8s distribution) into Docker containers.

Severed-Infra % tree
.
├── README.md
├── apps
│   ├── severed-blog-config.yaml
│   ├── severed-blog-hpa.yaml
│   ├── severed-blog-service.yaml
│   ├── severed-blog.yaml
│   └── severed-ingress.yaml
├── infra
│   ├── alloy-env.yaml
│   ├── alloy-setup.yaml
│   ├── dashboard
│   │   ├── dashboard-admin.yaml
│   │   ├── permanent-token.yaml
│   │   └── traefik-config.yaml
│   ├── observer
│   │   ├── adapter-values.yaml
│   │   ├── dashboard-json.yaml
│   │   ├── grafana-ingress.yaml
│   │   ├── grafana.yaml
│   │   ├── loki.yaml
│   │   └── prometheus.yaml
│   └── storage
│       └── openebs-sc.yaml
├── namespaces.yaml
└── scripts
    ├── README.md
    ├── access-hub.sh
    ├── deploy-all.sh
    ├── setup-grafana-creds.sh
    └── tests
        ├── generated-202-404-blog.sh
        └── stress-blog.sh

1.1 Multi-Node Simulation

Server (Control Plane): The master node. Runs the API server, scheduler, and etcd.
Agents (Workers): The worker nodes where our application pods run.

Setting up the environment

We map port 8080 to the internal Traefik LoadBalancer to access services via *.localhost.

k3d cluster create severed-cluster \
  --agents 2 \
  -p "8080:80@loadbalancer" \
  -p "8443:443@loadbalancer"

1.2 Image Registry Lifecycle

Since our severed-blog image is local, we side-load it directly into the cluster's internal image store rather than pushing to Docker Hub.

docker build -t severed-blog:v0.3 .
k3d image import severed-blog:v0.3 -c severed-cluster

1.3 Namespaces & Storage

We partition the cluster into logical domains. We also install OpenEBS to provide dynamic storage provisioning (PersistentVolumes) for our databases.

namespaces.yaml

apiVersion: v1
kind: Namespace
metadata:
  name: severed-apps
---
apiVersion: v1
kind: Namespace
metadata:
  name: monitoring
---
apiVersion: v1
kind: Namespace
metadata:
  name: kubernetes-dashboard
---
apiVersion: v1
kind: Namespace
metadata:
  name: openebs

infra/storage/openebs-sc.yaml

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: severed-storage
provisioner: openebs.io/local
reclaimPolicy: Delete
volumeBindingMode: WaitForFirstConsumer

1.4. Infrastructure Concepts Cheat Sheet

Object	Docker Equivalent	Kubernetes Purpose
Node	The Host Machine	A physical or virtual server in the cluster.
Pod	A Container	The smallest deployable unit (can contain multiple containers).
Deployments	`docker-compose up`	Manages the lifecycle and scaling of Pods.
Services	Network Aliases	Provides a stable DNS name/IP for a group of Pods.
HPA	Auto-Scaling Group	Automatically scales replicas based on traffic/load.
Ingress	Nginx Proxy / Traefik	Manages external access to Services via HTTP/HTTPS.
ConfigMap	`docker run -v config:/etc...`	Decouples configuration files from the container image.
Secret	Environment Variables (Secure)	Stores sensitive data (passwords, tokens) encoded in Base64.
DaemonSet	`mode: global` (Swarm)	Ensures one copy of a Pod runs on every Node (logs/monitoring).
StatefulSet	N/A	Manages apps requiring stable identities and storage (Databases).

2025-12-27-part-2

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