Challenge, Easy,  on  Kubernetes

Kubernetes Pod Scheduling: Topology Spread Constraints

Kaloyan Preslavski
by  Kaloyan Preslavski

topologySpreadConstraints gives you fine-grained control over how pods distribute across failure domains. Unlike pod anti-affinity which enforces at most one pod per domain, maxSkew sets the maximum allowed difference in pod count between any two domains.

Topology Spread Constraints - Kubernetes Docs

Verify the cluster - nodes are labeled with zone information:

kubectl get nodes --show-labels

cplane-01 and node-01 are in zone-a. node-02 is in zone-b.

Task 1 - Node-Level Spread

Deploy a web Deployment with 4 replicas spread across all 3 nodes. With maxSkew: 1, no node can have more than one extra pod compared to any other.

Steps:

  • Create Deployment named web, image nginx:alpine, 4 replicas, label app: web
  • topologySpreadConstraints with maxSkew: 1, topologyKey: kubernetes.io/hostname, whenUnsatisfiable: DoNotSchedule
kubectl get pods -l app=web -o wide
Hint: topologySpreadConstraints structure
topologySpreadConstraints:
- maxSkew: <number>
  topologyKey: <topology-key>
  whenUnsatisfiable: DoNotSchedule
  labelSelector:
    matchLabels:
      <label-key>: <label-value>

Task 2 - Zone-Level Spread

Deploy a zone-web Deployment with 4 replicas spread across availability zones instead of individual nodes. The topology key changes from hostname to zone - the scheduler now treats each zone as a single domain.

Steps:

  • Create Deployment named zone-web, image nginx:alpine, 4 replicas, label app: zone-web
  • topologySpreadConstraints with maxSkew: 1, topologyKey: topology.kubernetes.io/zone, whenUnsatisfiable: DoNotSchedule
kubectl get pods -l app=zone-web -o wide
Hint: Zone topology key
topologySpreadConstraints:
- maxSkew: <number>
  topologyKey: <zone-label-key>
  whenUnsatisfiable: DoNotSchedule
  labelSelector:
    matchLabels:
      <label-key>: <label-value>

This challenge is part of the Kubernetes Pod Scheduling skill path.

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labctl auth login

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