Mastering Kubernetes One Task at a Time - Know Thy Nodes!—Objective 6 - Schedule Pods on all Nodes (Worker + Control Plane)

schedule-on-all-nodes.sh

#!/usr/bin/bash

# Purpose: Mastering Kubernetes One Task at a Time - Know Thy Nodes!—Objective 6 - Schedule Pods on all Nodes (Worker + Control Plane)
# Blog Ref: https://medium.com/the-aws-way/the-aws-way-mastering-kubernetes-one-task-at-a-time-know-thy-nodes-e3ad157ac2db
# GitHub Ref: https://github.com/jdluther2020/jdluther-kubernetes-io-tasks/

# Author's NOTE
#  1. # are comment lines
#  2. Command output wherever helpful is shown inside {}
#  3. Everything is executed on a local dev environment (MacOS)

#
# OBJECTIVE 6 - SCHEDULE PODS ON ALL NODES (WORKER + CONTROL PLANE)
# - Create a deployment whose pods run on all nodes of the cluster
#

# Fist, check for the taints to see if any node including control plane that normally prevents pod scheduling
# We'll use the taint key to set the toleration next
kubectl describe nodes | grep -i -A 5 taints
{
Taints:             node-role.kubernetes.io/control-plane:NoSchedule
Unschedulable:      false
Lease:
  HolderIdentity:  basic-multi-node-cluster-control-plane
  AcquireTime:     <unset>
  RenewTime:       Thu, 06 Apr 2023 02:09:15 +0000
--
Taints:             <none>
Unschedulable:      false
Lease:
  HolderIdentity:  basic-multi-node-cluster-worker
  AcquireTime:     <unset>
  RenewTime:       Thu, 06 Apr 2023 02:09:14 +0000
--
Taints:             <none>
Unschedulable:      false
Lease:
  HolderIdentity:  basic-multi-node-cluster-worker2
  AcquireTime:     <unset>
  RenewTime:       Thu, 06 Apr 2023 02:09:22 +0000
}

# Create a deployment manifest with 3 replica pods to schedule one on each node (2 workers and 1 control plane)
cat <<EOF | tee deploy.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  creationTimestamp: null
  labels:
    app: nginx-deployment
  name: nginx-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx-deployment
  strategy: {}
  template:
    metadata:
      creationTimestamp: null
      labels:
        app: nginx-deployment
    spec:
      tolerations:
      - key: node-role.kubernetes.io/control-plane
        effect: NoSchedule
      containers:
      - image: nginx:latest
        name: nginx
        resources: {}
status: {}
EOF

# Create deployment
kubectl apply -f deploy.yaml
{
deployment.apps/nginx-deployment created
}

# Confirm each cluster node has one of the deployment pods
kubectl get pod -o wide
{
NAME                               READY   STATUS    RESTARTS   AGE     IP           NODE                                     NOMINATED NODE   READINESS GATES
nginx-deployment-98976f567-bkc66   1/1     Running   0          27s     10.244.2.3   basic-multi-node-cluster-worker2         <none>           <none>
nginx-deployment-98976f567-cd6m9   1/1     Running   0          27s     10.244.1.3   basic-multi-node-cluster-worker          <none>           <none>
nginx-deployment-98976f567-j7brf   1/1     Running   0          27s     10.244.0.5   basic-multi-node-cluster-control-plane   <none>           <none>
}

# Scale up the number of pods of the deployment from existing 3 to 9, and see how the scheduler distributes them among the 3 available nodes
kubectl scale deployment/nginx-deployment --replicas=9; kubectl rollout status deploy nginx-deployment
{
NAME                               READY   STATUS    RESTARTS   AGE     IP           NODE                                     NOMINATED NODE   READINESS GATES
nginx-deployment-98976f567-28dgg   1/1     Running   0          9s      10.244.1.5   basic-multi-node-cluster-worker          <none>           <none>
nginx-deployment-98976f567-7mkvc   1/1     Running   0          9s      10.244.2.6   basic-multi-node-cluster-worker2         <none>           <none>
nginx-deployment-98976f567-cd6m9   1/1     Running   0          2m1s    10.244.1.3   basic-multi-node-cluster-worker          <none>           <none>
nginx-deployment-98976f567-dhcpp   1/1     Running   0          9s      10.244.2.7   basic-multi-node-cluster-worker2         <none>           <none>
nginx-deployment-98976f567-j7brf   1/1     Running   0          2m1s    10.244.0.5   basic-multi-node-cluster-control-plane   <none>           <none>
nginx-deployment-98976f567-mw8jh   1/1     Running   0          9s      10.244.2.8   basic-multi-node-cluster-worker2         <none>           <none>
nginx-deployment-98976f567-qp8fn   1/1     Running   0          9s      10.244.0.6   basic-multi-node-cluster-control-plane   <none>           <none>
nginx-deployment-98976f567-qxm7g   1/1     Running   0          9s      10.244.0.7   basic-multi-node-cluster-control-plane   <none>           <none>
nginx-deployment-98976f567-tndks   1/1     Running   0          74s     10.244.1.4   basic-multi-node-cluster-worker          <none>           <none>
}

# END OF DEMONSTRATION