How To Avoid Placement of More Than One Pod Replicas on Same Worker Node

Problem

How to avoid assignment of multiple replicas of a pod on a single worker node?
How to configure deployment to avoid co-location of replicas on a single node?

Environment

Platform9 Managed Kubernetes - All Versions
Kube-Scheduler

Procedure

PodAntiAffinity can be configured to ensure that the scheduler does not co-locate replicas on a single node.
Below mentioned is the snippet of PodAntiAffinity configured for a Nginx deployment with 3 pod replicas.

podAntiAffinity Configuration
    
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# kubectl get deployment nginx-deployment -o yaml | grep -w "podAntiAffinity:" -A8        podAntiAffinity:          requiredDuringSchedulingIgnoredDuringExecution:          - labelSelector:              matchExpressions:              - key: app                operator: In                values:                - nginx            topologyKey: kubernetes.io/hostname
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This configuration makes sure that all 3 replicas of the pods are scheduled on three different nodes of the cluster.

kubectl output
    
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# kubectl get po -o wide -n defaultNAME                               READY   STATUS    RESTARTS    AGE       IP              NODE           nginx-deployment-84c6674589-cxp55   1/1     Running   0          55s     10.20.152.138   10.128.228.29   nginx-deployment-84c6674589-hzmnn   1/1     Running   0          55s     10.20.155.70    10.128.228.28   nginx-deployment-84c6674589-vq4l2   1/1     Running   0          55s     10.20.225.7     10.128.226.44
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Additional Information

Kubernetes Docs – Assigning Pods to Nodes

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