Application Patterns

Purpose: For application developers, provides reference patterns for stateless web apps, stateful services, batch jobs, and multi-environment promotion.

Overview

This reference covers four deployment patterns used in openCenter clusters. Each pattern includes the Kubernetes resource types involved, a minimal manifest example, and notes on when to use it.

Pattern 1 — Stateless Web Application

The most common pattern. A Deployment with an HPA, a Service, and an HTTPRoute.

Resources: Deployment, Service, HTTPRoute, HorizontalPodAutoscaler

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-frontend
  namespace: my-app
spec:
  replicas: 2
  selector:
    matchLabels:
      app: web-frontend
  template:
    metadata:
      labels:
        app: web-frontend
    spec:
      containers:
        - name: web-frontend
          image: harbor.opencenter.example.com/customer-apps/web-frontend:2.1.0-def456
          ports:
            - containerPort: 3000
          resources:
            requests:
              cpu: 100m
              memory: 128Mi
            limits:
              cpu: 1000m
              memory: 512Mi
      securityContext:
        runAsNonRoot: true
        seccompProfile:
          type: RuntimeDefault
---
apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  name: web-frontend
  namespace: my-app
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: web-frontend
  minReplicas: 2
  maxReplicas: 10
  metrics:
    - type: Resource
      resource:
        name: cpu
        target:
          type: Utilization
          averageUtilization: 70

When to use: HTTP APIs, SPAs, microservices that store no local state. Scale horizontally with HPA.

Pattern 2 — Stateful Service

For databases, caches, or message brokers that need stable network identity and persistent storage.

Resources: StatefulSet, Service (headless), PersistentVolumeClaim

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: postgres
  namespace: my-app
spec:
  serviceName: postgres
  replicas: 3
  selector:
    matchLabels:
      app: postgres
  template:
    metadata:
      labels:
        app: postgres
    spec:
      containers:
        - name: postgres
          image: harbor.opencenter.example.com/customer-apps/postgres:16.2-abc789
          ports:
            - containerPort: 5432
          volumeMounts:
            - name: data
              mountPath: /var/lib/postgresql/data
          resources:
            requests:
              cpu: 500m
              memory: 1Gi
            limits:
              cpu: 2000m
              memory: 4Gi
  volumeClaimTemplates:
    - metadata:
        name: data
      spec:
        accessModes: ["ReadWriteOnce"]
        storageClassName: longhorn
        resources:
          requests:
            storage: 50Gi

When to use: Databases, Redis clusters, Kafka brokers. Requires Longhorn or vSphere CSI for persistent volumes.

Pattern 3 — Batch Job

For one-off or scheduled workloads like data migrations, report generation, or ETL pipelines.

Resources: CronJob (or Job), ServiceAccount

apiVersion: batch/v1
kind: CronJob
metadata:
  name: nightly-report
  namespace: my-app
spec:
  schedule: "0 2 * * *"
  jobTemplate:
    spec:
      template:
        spec:
          containers:
            - name: report-generator
              image: harbor.opencenter.example.com/customer-apps/report-gen:1.0.0-fed321
              command: ["python", "generate_report.py"]
              resources:
                requests:
                  cpu: 500m
                  memory: 512Mi
                limits:
                  cpu: 2000m
                  memory: 2Gi
          restartPolicy: OnFailure
          securityContext:
            runAsNonRoot: true
  successfulJobsHistoryLimit: 3
  failedJobsHistoryLimit: 5

When to use: Scheduled tasks, data pipelines, migration scripts. Set activeDeadlineSeconds to prevent runaway jobs.

Pattern 4 — Multi-Environment with Kustomize Overlays

For applications that deploy to dev, staging, and production with environment-specific configuration.

Directory structure:

my-app/
├── base/
│   ├── kustomization.yaml
│   ├── deployment.yaml
│   ├── service.yaml
│   └── httproute.yaml
└── overlays/
    ├── dev/
    │   ├── kustomization.yaml
    │   └── patch-replicas.yaml
    ├── staging/
    │   ├── kustomization.yaml
    │   └── patch-replicas.yaml
    └── production/
        ├── kustomization.yaml
        └── patch-replicas.yaml

# overlays/production/kustomization.yaml
apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  - ../../base
patches:
  - path: patch-replicas.yaml
images:
  - name: my-app
    newName: harbor.opencenter.example.com/platform-production/my-app
    newTag: "2.1.0-def456"

# overlays/production/patch-replicas.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app
spec:
  replicas: 5

When to use: Any application that needs different replica counts, resource limits, image tags, or feature flags per environment. The platform team points each cluster's FluxCD Kustomization at the appropriate overlay path.

Pattern Comparison

Pattern	Scaling	Storage	Networking	Complexity
Stateless web app	HPA (horizontal)	None	HTTPRoute	Low
Stateful service	Manual or operator	PVC (Longhorn/CSI)	Headless Service	Medium
Batch job	N/A (runs to completion)	Optional	None (internal)	Low
Multi-environment	Per-overlay	Per-overlay	Per-overlay	Medium

Overview​

Pattern 1 — Stateless Web Application​

Pattern 2 — Stateful Service​

Pattern 3 — Batch Job​

Pattern 4 — Multi-Environment with Kustomize Overlays​

Pattern Comparison​

Further Reading​