Cluster Autoscaler configure on AWS EKS -1.24.

Introduction :
The Kubernetes Cluster Autoscaler automatically adjusts the number of nodes in your cluster when pods fail or are rescheduled onto other nodes. The Cluster Autoscaler uses Auto Scaling groups. For more information, see Cluster Autoscaler on AWS.

Step 1: Create a EKS Cluster

• performed Step 1 : to step 5 : Click here

Step 2: Verify how many nodes and pods are running
Node :

[root@ip-172-31-18-194 ~]# kubectl get nodes
NAME                            STATUS     ROLES    AGE     VERSION
ip-192-168-5-245.ec2.internal   Ready      <none>   4m19s   v1.24.17-eks-e71965b
ip-192-168-63-39.ec2.internal   Ready      <none>   2s      v1.24.17-eks-e71965b

Pods:

[root@ip-172-31-18-194 ~]# kubectl get po -A
NAMESPACE     NAME                       READY   STATUS    RESTARTS   AGE
kube-system   aws-node-4fdfg             1/1     Running   0          2m50s
kube-system   aws-node-mm84r             1/1     Running   0          2m53s
kube-system   coredns-79989457d9-798tx   1/1     Running   0          10m
kube-system   coredns-79989457d9-7fhzl   1/1     Running   0          10m
kube-system   kube-proxy-rkbzz           1/1     Running   0          2m50s
kube-system   kube-proxy-vfq7k           1/1     Running   0          2m53s

Step 3: Create a IAM OIDC Provider
IAM OIDC is used for authorizing the Cluster Autoscaler to launch or terminate instances under an Auto Scaling group.
Open EKS Dashboard and copy a OpenID Connect Provider link

• Open a IAM Providers
• Click “Add provider,” select “OpenID Connect,” and click “Get thumbprint” as shown below:
• Then enter the “Audience” (sts.amazonaws.com in our example pointing to the AWS STS, also known as the Security Token Service) and click the add provider
• Adding identity information on identity providers Step 4: Create IAM Policy Create a Policy with necessary permission.
• To create the policy with the necessary permissions, save the below file as AmazonEKSClusterAutoscalerPolicy

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "autoscaling:DescribeAutoScalingGroups",
                "autoscaling:DescribeAutoScalingInstances",
                "autoscaling:DescribeLaunchConfigurations",
                "autoscaling:DescribeScalingActivities",
                "autoscaling:DescribeTags",
                "ec2:DescribeInstanceTypes",
                "ec2:DescribeLaunchTemplateVersions"
            ],
            "Resource": [
                "*"
            ]
        },
        {
            "Effect": "Allow",
            "Action": [
                "autoscaling:SetDesiredCapacity",
                "autoscaling:TerminateInstanceInAutoScalingGroup",
                "ec2:DescribeImages",
                "ec2:GetInstanceTypesFromInstanceRequirements",
                "eks:DescribeNodegroup"
            ],
            "Resource": [
                "*"
            ]
        }
    ]
}

• Review and create a policy Step 5 : Create a IAM Role for the provider. Create role Select the web identity

• Select identity provide and audience click next.
  

• Add Policy AmazonEKSClusterAutoscalerPolicy
  
  Click Next and provide Role Name : EKS_Autoscaler
  

• verify the IAM role and make sure the policy is attached. Edit the “Trust relationships.” Before Edit “Trust relationships.”

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": {
                "Federated": "arn:aws:iam::256050093938:oidc-provider/oidc.eks.us-east-1.amazonaws.com/id/CD6440D4E14822FC649C070BD8C41A96"
            },
            "Action": "sts:AssumeRoleWithWebIdentity",
            "Condition": {
                "StringEquals": {
                    "oidc.eks.us-east-1.amazonaws.com/id/CD6440D4E14822FC649C070BD8C41A96:aud": "sts.amazonaws.com"
                }
            }
        }
    ]
}

• After Edit “Trust relationships.”

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": {
                "Federated": "arn:aws:iam::256050093938:oidc-provider/oidc.eks.us-east-1.amazonaws.com/id/CD6440D4E14822FC649C070BD8C41A96"
            },
            "Action": "sts:AssumeRoleWithWebIdentity",
            "Condition": {
                "StringEquals": {
                    "oidc.eks.us-east-1.amazonaws.com/id/CD6440D4E14822FC649C070BD8C41A96:aud": "sts.amazonaws.com",
                    "oidc.eks.us-east-1.amazonaws.com/id/CD6440D4E14822FC649C070BD8C41A96:sub": "system:serviceaccount:kube-system:cluster-autoscaler"
                }
            }
        }
    ]
}

Step 6 : Deploy a Cluster Autoscaler
Next, we deploy Cluster Autoscaler. To do so, you must use the Amazon Resource Names (ARN) number of the IAM role created in our earlier step.
The content intended to save into a file (make sure you copy all of the content presented over the next page):
Modify below two lines

• Line 8 : change IAM Role name
• Line 159 : --node-group-auto-discovery = This is used by CA to discover the Auto Scaling group based on its tag.

apiVersion: v1
kind: ServiceAccount
metadata:
  labels:
    k8s-addon: cluster-autoscaler.addons.k8s.io
    k8s-app: cluster-autoscaler
  annotations:
    eks.amazonaws.com/role-arn: arn:aws:iam::256050093938:role/EKS_Autoscaler
  name: cluster-autoscaler
  namespace: kube-system
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: cluster-autoscaler
  labels:
    k8s-addon: cluster-autoscaler.addons.k8s.io
    k8s-app: cluster-autoscaler
rules:
  - apiGroups: [""]
    resources: ["events", "endpoints"]
    verbs: ["create", "patch"]
  - apiGroups: [""]
    resources: ["pods/eviction"]
    verbs: ["create"]
  - apiGroups: [""]
    resources: ["pods/status"]
    verbs: ["update"]
  - apiGroups: [""]
    resources: ["endpoints"]
    resourceNames: ["cluster-autoscaler"]
    verbs: ["get", "update"]
  - apiGroups: [""]
    resources: ["nodes"]
    verbs: ["watch", "list", "get", "update"]
  - apiGroups: [""]
    resources:
      - "pods"
      - "services"
      - "replicationcontrollers"
      - "persistentvolumeclaims"
      - "persistentvolumes"
    verbs: ["watch", "list", "get"]
  - apiGroups: ["extensions"]
    resources: ["replicasets", "daemonsets"]
    verbs: ["watch", "list", "get"]
  - apiGroups: ["policy"]
    resources: ["poddisruptionbudgets"]
    verbs: ["watch", "list"]
  - apiGroups: ["apps"]
    resources: ["statefulsets", "replicasets", "daemonsets"]
    verbs: ["watch", "list", "get"]
  - apiGroups: ["storage.k8s.io"]
    resources: ["storageclasses", "csinodes"]
    verbs: ["watch", "list", "get"]
  - apiGroups: ["batch", "extensions"]
    resources: ["jobs"]
    verbs: ["get", "list", "watch", "patch"]
  - apiGroups: ["coordination.k8s.io"]
    resources: ["leases"]
    verbs: ["create"]
  - apiGroups: ["coordination.k8s.io"]
    resourceNames: ["cluster-autoscaler"]
    resources: ["leases"]
    verbs: ["get", "update"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: cluster-autoscaler
  namespace: kube-system
  labels:
    k8s-addon: cluster-autoscaler.addons.k8s.io
    k8s-app: cluster-autoscaler
rules:
  - apiGroups: [""]
    resources: ["configmaps"]
    verbs: ["create","list","watch"]
  - apiGroups: [""]
    resources: ["configmaps"]
    resourceNames: ["cluster-autoscaler-status", "cluster-autoscaler-priority-expander"]
    verbs: ["delete", "get", "update", "watch"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: cluster-autoscaler
  labels:
    k8s-addon: cluster-autoscaler.addons.k8s.io
    k8s-app: cluster-autoscaler
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: cluster-autoscaler
subjects:
  - kind: ServiceAccount
    name: cluster-autoscaler
    namespace: kube-system
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: cluster-autoscaler
  namespace: kube-system
  labels:
    k8s-addon: cluster-autoscaler.addons.k8s.io
    k8s-app: cluster-autoscaler
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: Role
  name: cluster-autoscaler
subjects:
  - kind: ServiceAccount
    name: cluster-autoscaler
    namespace: kube-system
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: cluster-autoscaler
  namespace: kube-system
  labels:
    app: cluster-autoscaler
spec:
  replicas: 1
  selector:
    matchLabels:
      app: cluster-autoscaler
  template:
    metadata:
      labels:
        app: cluster-autoscaler
      annotations:
        cluster-autoscaler.kubernetes.io/safe-to-evict: 'false'
    spec:
      serviceAccountName: cluster-autoscaler
      containers:
        - image: k8s.gcr.io/autoscaling/cluster-autoscaler:v1.20.0
          name: cluster-autoscaler
          resources:
            limits:
              cpu: 100m
              memory: 500Mi
            requests:
              cpu: 100m
              memory: 500Mi
          command:
            - ./cluster-autoscaler
            - --v=4
            - --stderrthreshold=info
            - --cloud-provider=aws
            - --skip-nodes-with-local-storage=false
            - --expander=least-waste
            - --node-group-auto-discovery=asg:tag=k8s.io/cluster-autoscaler/enabled,k8s.io/cluster-autoscaler/ashish
            - --balance-similar-node-groups
            - --skip-nodes-with-system-pods=false
          volumeMounts:
            - name: ssl-certs
              mountPath: /etc/ssl/certs/ca-certificates.crt #/etc/ssl/certs/ca-bundle.crt for Amazon Linux Worker Nodes
              readOnly: true
          imagePullPolicy: "Always"
      volumes:
        - name: ssl-certs
          hostPath:
            path: "/etc/ssl/certs/ca-bundle.crt"

To deploy CA, save the following content presented after the command below in a file and run this provided command:

kubectl apply -f cluster-autoscaler.yaml
serviceaccount/cluster-autoscaler created
clusterrole.rbac.authorization.k8s.io/cluster-autoscaler created
role.rbac.authorization.k8s.io/cluster-autoscaler created
clusterrolebinding.rbac.authorization.k8s.io/cluster-autoscaler created
rolebinding.rbac.authorization.k8s.io/cluster-autoscaler created
deployment.apps/cluster-autoscaler created

The expected results are displayed below.

[root@ip-172-31-18-194 ~]# kubectl get po -A
NAMESPACE     NAME                                  READY   STATUS    RESTARTS   AGE
kube-system   aws-node-2frzk                        1/1     Running   0          67m
kube-system   aws-node-drmtr                        1/1     Running   0          63m
kube-system   cluster-autoscaler-657d67cd5d-l7q4m   1/1     Running   0          8s
kube-system   coredns-79989457d9-89f48              1/1     Running   0          75m
kube-system   coredns-79989457d9-ddvvb              1/1     Running   0          75m
kube-system   kube-proxy-hpzxj                      1/1     Running   0          63m
kube-system   kube-proxy-vb2gj                      1/1     Running   0          67m

The expected results are displayed below.

[root@ip-172-31-18-194 ~]# kubectl get nodes
NAME                            STATUS   ROLES    AGE   VERSION
ip-192-168-5-245.ec2.internal   Ready    <none>   76m   v1.24.17-eks-e71965b
ip-192-168-63-39.ec2.internal   Ready    <none>   72m   v1.24.17-eks-e71965b

Troubleshoot :
verify the logs by issuing this command:

kubectl logs -l app=cluster-autoscaler -n kubesystem -f

Conclusion :
Cluster Autoscaler plays a vital role in a Kubernetes cluster by ensuring adequate computing resources are available by adding the nodes to a cluster and keeping infrastructure costs down by removing nodes