What is Kubernetes Topology Spread Constraints?

Question

Accepted Answer

**Topology Spread** — evenly distribute Pods across topology domains.

```yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
spec:
  replicas: 6
  template:
    spec:
      topologySpreadConstraints:
      - maxSkew: 1
        topologyKey: topology.kubernetes.io/zone
        whenUnsatisfiable: DoNotSchedule
        labelSelector:
          matchLabels:
            app: myapp
      - maxSkew: 2
        topologyKey: kubernetes.io/hostname
        whenUnsatisfiable: ScheduleAnyway
        labelSelector:
          matchLabels:
            app: myapp
        matchLabelKeys:
        - pod-template-hash
        nodeAffinityPolicy: Honor
        nodeTaintsPolicy: Honor
      containers:
      - name: app
        image: myapp:latest
```

```bash
# Commands
kubectl get pods -o wide  # Check Pod distribution

# Check zone distribution
kubectl get pods -o json | jq '.items[] | {name: .metadata.name, node: .spec.nodeName}'

# Verify node zones
kubectl get nodes -o custom-columns=NAME:.metadata.name,ZONE:.metadata.labels.topology\.kubernetes\.io/zone

# Check constraint status
kubectl get deployment myapp -o jsonpath='{.spec.template.spec.topologySpreadConstraints}' | jq

# View unschedulable Pods
kubectl get events --field-selector reason=FailedScheduling
```

**Parameters:**
- maxSkew: maximum difference between domains.
- topologyKey: label for domain grouping.
- whenUnsatisfiable: DoNotSchedule or ScheduleAnyway.

**Use cases:**
- Multi-zone distribution.
- Cross-node distribution.
- HA across failure domains.

DevOps: What is Kubernetes Topology Spread Constraints?