Bits of .NET

🗺️ Spread Pods Across Zones, Nodes, Racks

All pods on same node? Node failure = downtime. Topology spread constraints spread pods evenly across zones, nodes, or custom domains.

📝 Pod Topology Spread

apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
spec:
  replicas: 6
  template:
    spec:
      topologySpreadConstraints:
      - maxSkew: 1
        topologyKey: kubernetes.io/hostname
        whenUnsatisfiable: DoNotSchedule
        labelSelector:
          matchLabels:
            app: myapp
      - maxSkew: 1
        topologyKey: topology.kubernetes.io/zone
        whenUnsatisfiable: ScheduleAnyway
        labelSelector:
          matchLabels:
            app: myapp
      containers:
      - name: app
        image: myapp:latest

🎯 Understanding Parameters

maxSkew: The maximum difference in pod count between any two domains
topologyKey: Node label to define domains (hostname, zone, region)
whenUnsatisfiable:
  - DoNotSchedule: Don't schedule if constraint can't be met
  - ScheduleAnyway: Schedule but try to minimize skew
labelSelector: Which pods to consider for spread

✅ Example: 3 Zones, 6 Replicas

• Zone A: 2 pods
• Zone B: 2 pods
• Zone C: 2 pods
• Within each zone: spread across nodes
• maxSkew: 1 ensures no zone has +1 pod more than others