Usage

For an applied example, see Showcase.

Kubernetes Structure

The diagram below represents a basic web application. An Ingress controls where traffic from the Internet is routed. Depending on the path, a Service is exposed, which selects Pods. The selection is made using Labels (represented as dotted lines.) Deployments control the Pods, which are wrappers for Containers. The Backend Pods communicate with the Database using the Database Service, which is discoverable from within the Backend Pods using DNS. The Database persists data using a Persistent Volume Claim (PVC).

flowchart LR
    A[Web] -->|*.app.konst.fish| B(Ingress)
    B -->|/api| C{{Backend Service}}
    subgraph Backend
    C-. app=backend .-> D[Backend Pod]
    C-. app=backend .-> E[Backend Pod]
    H(Backend Deployment) --> D
    H --> E
    end

    B -->|/| F{{Frontend Service}}
    subgraph Frontend
    F-. app=frontend .-> G[Frontend Pod]
    I(Frontend Deployment) --> G
    end

    subgraph Database
    D --> J{{Database Service}}
    E --> J
    J -. app=db .-> K[Database Pod]
    L(Database StatefulSet) --> K
    K --> M[(Database PVC)]
    end

Kubernetes Manifests

Deployment

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  selector:
    matchLabels:
      app: nginx
  replicas: 2
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx-pod
        image: nginx:latest
        resources:
          limits:
            memory: "128Mi"
            cpu: "500m"
          requests:
            memory: "64Mi"
            cpu: "250m"
        ports:
        - containerPort: 80

Service

apiVersion: v1
kind: Service
metadata:
  name: nginx-service
spec:
  selector:
    app: nginx
  ports:
  - port: 80
    targetPort: 80
 

Ingress

Also see Ingress Nginx

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: nginx-ingress
  labels:
    name: nginx-ingress
  annotations:
    cert-manager.io/issuer: "appdomain"
spec:
  tls:
  - hosts:
    - test.app.konst.fish
    secretName: test-tls
  ingressClassName: nginx
  rules:
  - host: test.app.konst.fish
    http:
      paths:
      - pathType: Prefix
        path: "/"
        backend:
          service:
            name: nginx-service
            port: 
              number: 80

Persistent Volume Claim (PVC)

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: test-pvc
spec:
  accessModes:
    - ReadWriteOnce
  volumeMode: Filesystem
  resources:
    requests:
      storage: 10Gi
  storageClassName: hcloud-volumes

Deployments