Bits of .NET

👯 Keep Related Pods Close (or Far Apart)

Cache and app should be on same node. Database replicas should be on different nodes. Pod affinity/anti-affinity controls pod placement.

📝 Pod Affinity (Same Node)

apiVersion: v1
kind: Pod
metadata:
  name: web-app
spec:
  affinity:
    podAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
      - labelSelector:
          matchLabels:
            app: cache
        topologyKey: kubernetes.io/hostname
  containers:
  - name: app
    image: myapp

# Web pod will be scheduled on same node as cache pod

🚫 Pod Anti-Affinity (Different Nodes)

apiVersion: apps/v1
kind: Deployment
metadata:
  name: database
spec:
  replicas: 3
  template:
    spec:
      affinity:
        podAntiAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
          - labelSelector:
              matchLabels:
                app: database
            topologyKey: kubernetes.io/hostname
      containers:
      - name: db
        image: postgres

# Database replicas will NEVER be on same node (high availability)

✅ Preferred (Best Effort) vs Required (Hard Constraint)

• requiredDuringScheduling: Must satisfy (hard constraint)
• preferredDuringScheduling: Try to satisfy (soft constraint)
• Use ‘preferred’ for performance optimization
• Use ‘required’ for security/compliance