Cluster Autoscaler with AWS EC2 Auto Scaling Groups

This guide will show you how to install and use Kubernetes cluster-autoscaler on Rancher custom clusters using AWS EC2 Auto Scaling Groups.

We are going to install a Rancher RKE custom cluster with a fixed number of nodes with the etcd and controlplane roles, and a variable nodes with the worker role, managed by cluster-autoscaler.

• Prerequisites
• 1. Create a Custom Cluster
• 2. Configure the Cloud Provider
• 3. Deploy Nodes
• 4. Install cluster-autoscaler
  • Parameters
  • Deployment
• Testing
  • Generating Load
  • Checking Scale

Prerequisites

These elements are required to follow this guide:

• The Rancher server is up and running
• You have an AWS EC2 user with proper permissions to create virtual machines, auto scaling groups, and IAM profiles and roles

1. Create a Custom Cluster

On Rancher server, we should create a custom k8s cluster v1.18.x. Be sure that cloud_provider name is set to amazonec2. Once cluster is created we need to get:

• clusterID: c-xxxxx will be used on EC2 kubernetes.io/cluster/<clusterID> instance tag
• clusterName: will be used on EC2 k8s.io/cluster-autoscaler/<clusterName> instance tag

• nodeCommand: will be added on EC2 instance user_data to include new nodes on cluster

  sudo docker run -d --privileged --restart=unless-stopped --net=host -v /etc/kubernetes:/etc/kubernetes -v /var/run:/var/run rancher/rancher-agent:<RANCHER_VERSION> --server https://<RANCHER_URL> --token <RANCHER_TOKEN> --ca-checksum <RANCHER_CHECKSUM> <roles>

2. Configure the Cloud Provider

On AWS EC2, we should create a few objects to configure our system. We’ve defined three distinct groups and IAM profiles to configure on AWS.

1. Autoscaling group: Nodes that will be part of the EC2 Auto Scaling Group (ASG). The ASG will be used by cluster-autoscaler to scale up and down.

   • IAM profile: Required by k8s nodes where cluster-autoscaler will be running. It is recommended for Kubernetes master nodes. This profile is called K8sAutoscalerProfile.

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

2. Master group: Nodes that will be part of the Kubernetes etcd and/or control planes. This will be out of the ASG.

   • IAM profile: Required by the Kubernetes cloud_provider integration. Optionally, AWS_ACCESS_KEY and AWS_SECRET_KEY can be used instead using-aws-credentials. This profile is called K8sMasterProfile.

     {
         "Version": "2012-10-17",
         "Statement": [
             {
                 "Effect": "Allow",
                 "Action": [
                     "autoscaling:DescribeAutoScalingGroups",
                     "autoscaling:DescribeLaunchConfigurations",
                     "autoscaling:DescribeTags",
                     "ec2:DescribeInstances",
                     "ec2:DescribeRegions",
                     "ec2:DescribeRouteTables",
                     "ec2:DescribeSecurityGroups",
                     "ec2:DescribeSubnets",
                     "ec2:DescribeVolumes",
                     "ec2:CreateSecurityGroup",
                     "ec2:CreateTags",
                     "ec2:CreateVolume",
                     "ec2:ModifyInstanceAttribute",
                     "ec2:ModifyVolume",
                     "ec2:AttachVolume",
                     "ec2:AuthorizeSecurityGroupIngress",
                     "ec2:CreateRoute",
                     "ec2:DeleteRoute",
                     "ec2:DeleteSecurityGroup",
                     "ec2:DeleteVolume",
                     "ec2:DetachVolume",
                     "ec2:RevokeSecurityGroupIngress",
                     "ec2:DescribeVpcs",
                     "elasticloadbalancing:AddTags",
                     "elasticloadbalancing:AttachLoadBalancerToSubnets",
                     "elasticloadbalancing:ApplySecurityGroupsToLoadBalancer",
                     "elasticloadbalancing:CreateLoadBalancer",
                     "elasticloadbalancing:CreateLoadBalancerPolicy",
                     "elasticloadbalancing:CreateLoadBalancerListeners",
                     "elasticloadbalancing:ConfigureHealthCheck",
                     "elasticloadbalancing:DeleteLoadBalancer",
                     "elasticloadbalancing:DeleteLoadBalancerListeners",
                     "elasticloadbalancing:DescribeLoadBalancers",
                     "elasticloadbalancing:DescribeLoadBalancerAttributes",
                     "elasticloadbalancing:DetachLoadBalancerFromSubnets",
                     "elasticloadbalancing:DeregisterInstancesFromLoadBalancer",
                     "elasticloadbalancing:ModifyLoadBalancerAttributes",
                     "elasticloadbalancing:RegisterInstancesWithLoadBalancer",
                     "elasticloadbalancing:SetLoadBalancerPoliciesForBackendServer",
                     "elasticloadbalancing:AddTags",
                     "elasticloadbalancing:CreateListener",
                     "elasticloadbalancing:CreateTargetGroup",
                     "elasticloadbalancing:DeleteListener",
                     "elasticloadbalancing:DeleteTargetGroup",
                     "elasticloadbalancing:DescribeListeners",
                     "elasticloadbalancing:DescribeLoadBalancerPolicies",
                     "elasticloadbalancing:DescribeTargetGroups",
                     "elasticloadbalancing:DescribeTargetHealth",
                     "elasticloadbalancing:ModifyListener",
                     "elasticloadbalancing:ModifyTargetGroup",
                     "elasticloadbalancing:RegisterTargets",
                     "elasticloadbalancing:SetLoadBalancerPoliciesOfListener",
                     "iam:CreateServiceLinkedRole",
                     "ecr:GetAuthorizationToken",
                     "ecr:BatchCheckLayerAvailability",
                     "ecr:GetDownloadUrlForLayer",
                     "ecr:GetRepositoryPolicy",
                     "ecr:DescribeRepositories",
                     "ecr:ListImages",
                     "ecr:BatchGetImage",
                     "kms:DescribeKey"
                 ],
                 "Resource": [
                     "*"
                 ]
             }
         ]
     }

   • IAM role: K8sMasterRole: [K8sMasterProfile,K8sAutoscalerProfile]
   • Security group: K8sMasterSg More info atRKE ports (custom nodes tab)
   • Tags: kubernetes.io/cluster/<clusterID>: owned
   • User data: K8sMasterUserData Ubuntu 18.04(ami-0e11cbb34015ff725), installs docker and add etcd+controlplane node to the k8s cluster

     #!/bin/bash -x
     cat <<EOF > /etc/sysctl.d/90-kubelet.conf
     vm.overcommit_memory = 1
     vm.panic_on_oom = 0
     kernel.panic = 10
     kernel.panic_on_oops = 1
     kernel.keys.root_maxkeys = 1000000
     kernel.keys.root_maxbytes = 25000000
     EOF
     sysctl -p /etc/sysctl.d/90-kubelet.conf
     curl -sL https://releases.rancher.com/install-docker/19.03.sh | sh
     sudo usermod -aG docker ubuntu
     TOKEN=$(curl -s -X PUT "http://169.254.169.254/latest/api/token" -H "X-aws-ec2-metadata-token-ttl-seconds: 21600")
     PRIVATE_IP=$(curl -H "X-aws-ec2-metadata-token: ${TOKEN}" -s http://169.254.169.254/latest/meta-data/local-ipv4)
     PUBLIC_IP=$(curl -H "X-aws-ec2-metadata-token: ${TOKEN}" -s http://169.254.169.254/latest/meta-data/public-ipv4)
     K8S_ROLES="--etcd --controlplane"
     sudo docker run -d --privileged --restart=unless-stopped --net=host -v /etc/kubernetes:/etc/kubernetes -v /var/run:/var/run rancher/rancher-agent:<RANCHER_VERSION> --server https://<RANCHER_URL> --token <RANCHER_TOKEN> --ca-checksum <RANCHER_CA_CHECKSUM> --address ${PUBLIC_IP} --internal-address ${PRIVATE_IP} ${K8S_ROLES}

3. Worker group: Nodes that will be part of the k8s worker plane. Worker nodes will be scaled by cluster-autoscaler using the ASG.

   • IAM profile: Provides cloud_provider worker integration. This profile is called K8sWorkerProfile.

     {
         "Version": "2012-10-17",
         "Statement": [
             {
                 "Effect": "Allow",
                 "Action": [
                     "ec2:DescribeInstances",
                     "ec2:DescribeRegions",
                     "ecr:GetAuthorizationToken",
                     "ecr:BatchCheckLayerAvailability",
                     "ecr:GetDownloadUrlForLayer",
                     "ecr:GetRepositoryPolicy",
                     "ecr:DescribeRepositories",
                     "ecr:ListImages",
                     "ecr:BatchGetImage"
                 ],
                 "Resource": "*"
             }
         ]
     }

   • IAM role: K8sWorkerRole: [K8sWorkerProfile]
   • Security group: K8sWorkerSg More info at RKE ports (custom nodes tab)
   • Tags:
   • kubernetes.io/cluster/<clusterID>: owned
   • k8s.io/cluster-autoscaler/<clusterName>: true
   • k8s.io/cluster-autoscaler/enabled: true
   • User data: K8sWorkerUserData Ubuntu 18.04(ami-0e11cbb34015ff725), installs docker and add worker node to the k8s cluster

     #!/bin/bash -x
     cat <<EOF > /etc/sysctl.d/90-kubelet.conf
     vm.overcommit_memory = 1
     vm.panic_on_oom = 0
     kernel.panic = 10
     kernel.panic_on_oops = 1
     kernel.keys.root_maxkeys = 1000000
     kernel.keys.root_maxbytes = 25000000
     EOF
     sysctl -p /etc/sysctl.d/90-kubelet.conf
     curl -sL https://releases.rancher.com/install-docker/19.03.sh | sh
     sudo usermod -aG docker ubuntu
     TOKEN=$(curl -s -X PUT "http://169.254.169.254/latest/api/token" -H "X-aws-ec2-metadata-token-ttl-seconds: 21600")
     PRIVATE_IP=$(curl -H "X-aws-ec2-metadata-token: ${TOKEN}" -s http://169.254.169.254/latest/meta-data/local-ipv4)
     PUBLIC_IP=$(curl -H "X-aws-ec2-metadata-token: ${TOKEN}" -s http://169.254.169.254/latest/meta-data/public-ipv4)
     K8S_ROLES="--worker"
     sudo docker run -d --privileged --restart=unless-stopped --net=host -v /etc/kubernetes:/etc/kubernetes -v /var/run:/var/run rancher/rancher-agent:<RANCHER_VERSION> --server https://<RANCHER_URL> --token <RANCHER_TOKEN> --ca-checksum <RANCHER_CA_CHECKCSUM> --address ${PUBLIC_IP} --internal-address ${PRIVATE_IP} ${K8S_ROLES}

More info is at RKE clusters on AWS and Cluster Autoscaler on AWS.

3. Deploy Nodes

Once we’ve configured AWS, let’s create VMs to bootstrap our cluster:

• master (etcd+controlplane): Depending your needs, deploy three master instances with proper size. More info is at the recommendations for production-ready clusters.

  • IAM role: K8sMasterRole
  • Security group: K8sMasterSg
  • Tags:
  • kubernetes.io/cluster/<clusterID>: owned
  • User data: K8sMasterUserData

• worker: Define an ASG on EC2 with the following settings:

  • Name: K8sWorkerAsg
  • IAM role: K8sWorkerRole
  • Security group: K8sWorkerSg
  • Tags:
  • kubernetes.io/cluster/<clusterID>: owned
  • k8s.io/cluster-autoscaler/<clusterName>: true
  • k8s.io/cluster-autoscaler/enabled: true
  • User data: K8sWorkerUserData
  • Instances:
  • minimum: 2
  • desired: 2
  • maximum: 10

Once the VMs are deployed, you should have a Rancher custom cluster up and running with three master and two worker nodes.

4. Install Cluster-autoscaler

At this point, we should have rancher cluster up and running. We are going to install cluster-autoscaler on master nodes and kube-system namespace, following cluster-autoscaler recommendation.

Parameters

This table shows cluster-autoscaler parameters for fine tuning:

Deployment

Based on cluster-autoscaler-run-on-master.yaml example, we’ve created our own cluster-autoscaler-deployment.yaml to use preferred auto-discovery setup, updating tolerations, nodeSelector, image version and command config:

---
apiVersion: v1
kind: ServiceAccount
metadata:
  labels:
    k8s-addon: cluster-autoscaler.addons.k8s.io
    k8s-app: cluster-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:
        prometheus.io/scrape: 'true'
        prometheus.io/port: '8085'
    spec:
      serviceAccountName: cluster-autoscaler
      tolerations:
        - effect: NoSchedule
          operator: "Equal"
          value: "true"
          key: node-role.kubernetes.io/controlplane
      nodeSelector:
        node-role.kubernetes.io/controlplane: "true"
      containers:
        - image: eu.gcr.io/k8s-artifacts-prod/autoscaling/cluster-autoscaler:v1.18.1
          name: cluster-autoscaler
          resources:
            limits:
              cpu: 100m
              memory: 300Mi
            requests:
              cpu: 100m
              memory: 300Mi
          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/<clusterName>
          volumeMounts:
            - name: ssl-certs
              mountPath: /etc/ssl/certs/ca-certificates.crt
              readOnly: true
          imagePullPolicy: "Always"
      volumes:
        - name: ssl-certs
          hostPath:
            path: "/etc/ssl/certs/ca-certificates.crt"

Once the manifest file is prepared, deploy it in the Kubernetes cluster (Rancher UI can be used instead):

kubectl -n kube-system apply -f cluster-autoscaler-deployment.yaml

Note: Cluster-autoscaler deployment can also be set up using manual configuration

Testing

At this point, we should have a cluster-scaler up and running in our Rancher custom cluster. Cluster-scale should manage K8sWorkerAsg ASG to scale up and down between 2 and 10 nodes, when one of the following conditions is true:

• There are pods that failed to run in the cluster due to insufficient resources. In this case, the cluster is scaled up.
• There are nodes in the cluster that have been underutilized for an extended period of time and their pods can be placed on other existing nodes. In this case, the cluster is scaled down.

Generating Load

We’ve prepared a test-deployment.yaml just to generate load on the Kubernetes cluster and see if cluster-autoscaler is working properly. The test deployment is requesting 1000m CPU and 1024Mi memory by three replicas. Adjust the requested resources and/or replica to be sure you exhaust the Kubernetes cluster resources:

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: hello-world
  name: hello-world
spec:
  replicas: 3
  selector:
    matchLabels:
      app: hello-world
  strategy:
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 0
    type: RollingUpdate
  template:
    metadata:
      labels:
        app: hello-world
    spec:
      containers:
      - image: rancher/hello-world
        imagePullPolicy: Always
        name: hello-world
        ports:
        - containerPort: 80
          protocol: TCP
        resources:
          limits:
            cpu: 1000m
            memory: 1024Mi
          requests:
            cpu: 1000m
            memory: 1024Mi

Once the test deployment is prepared, deploy it in the Kubernetes cluster default namespace (Rancher UI can be used instead):

kubectl -n default apply -f test-deployment.yaml

Checking Scale

Once the Kubernetes resources got exhausted, cluster-autoscaler should scale up worker nodes where pods failed to be scheduled. It should scale up until up until all pods became scheduled. You should see the new nodes on the ASG and on the Kubernetes cluster. Check the logs on the kube-system cluster-autoscaler pod.

Once scale up is checked, let check for scale down. To do it, reduce the replica number on the test deployment until you release enough Kubernetes cluster resources to scale down. You should see nodes disappear on the ASG and on the Kubernetes cluster. Check the logs on the kube-system cluster-autoscaler pod.