vertical-pod-autoscaler/

Vertical Pod Autoscaler

Intro

Vertical Pod Autoscaler (VPA) frees the users from necessity of setting up-to-date resource requests for the containers in their pods. When configured, it will set the requests automatically based on usage and thus allow proper scheduling onto nodes so that appropriate resource amount is available for each pod.

Autoscaling is configured with a Custom Resource Definition object called VerticalPodAutoscaler. It allows to specify which pods should be under vertically autoscaled as well as if/how the resource recommendations are applied.

To enable vertical pod autoscaling on your cluster please follow the installation procedure described below.

Installation

Notice on the backwards compatibility

During alpha the VPA CRD object may evolve in a way that is not compatible between releases. If you install a new release of VPA it is safest to delete the existing VPA CRD objects. Note that this will happen automatically if you just use the vpa-down.sh script to tear down the old installation of VPA.

Prerequisites

• It is strongly recommended to use Kubernetes 1.9 or greater. Your cluster must support MutatingAdmissionWebhooks, which are enabled by default since 1.9 (#58255). Read more about VPA Admission Webhook.
• kubectl should be connected to the cluster you want to install VPA in.
• The metrics server must be deployed in your cluster. Read more about Metrics Server.
• If you are using a GKE Kubernetes cluster, you will need to grant your current Google identity cluster-admin role. Otherwise you won't be authorized to grant extra privileges to the VPA system components.

  $ gcloud info | grep Account    # get current google identity
  Account: [myname@example.org]
  
  $ kubectl create clusterrolebinding myname-cluster-admin-binding --clusterrole=cluster-admin --user=myname@example.org
  Clusterrolebinding "myname-cluster-admin-binding" created
  

• If you already have another version of VPA installed in your cluster, you have to tear down the existing installation first with:

  ./hack/vpa-down.sh
  

Install command

To install VPA, please download the source code of VPA (for example with git clone https://github.com/kubernetes/autoscaler.git) and run the following command inside the vertical-pod-autoscaler directory:

./hack/vpa-up.sh

Note: the script currently reads environment variables: $REGISTRY and $TAG. Make sure you leave them unset unless you want to use a non-default version of VPA.

The script issues multiple kubectl commands to the cluster that insert the configuration and start all needed pods (see architecture) in the kube-system namespace. It also generates and uploads a secret (a CA cert) used by VPA Admission Controller when communicating with the API server.

Quick start

After installation the system is ready to recommend and set resource requests for your pods. In order to use it you need to insert a Vertical Pod Autoscaler resource for each logical group of pods that have similar resource requirements. We recommend to insert a VPA per each Deployment you want to control automatically and use the same label selector as the Deployment uses. There are three modes in which VPAs operate:

• "Auto": VPA assigns resource requests on pod creation as well as updates them on existing pods using the preferred update mechanism. Currently this is equivalent to "Recreate" (see below). Once restart free ("in-place") update of pod requests is available, it may be used as the preferred update mechanism by the "Auto" mode.
• "Recreate": VPA assigns resource requests on pod creation as well as updates them on existing pods by evicting them when the requested resources differ significantly from the new recommendation (respecting the Pod Distruption Budget, if defined). This mode should be used rarely, only if you need to ensure that the pods are restarted whenever the resource request changes. Otherwise prefer the "Auto" mode which may take advantage of restart free updates once they are available.
• "Initial": VPA only assigns resource requests on pod creation and never changes them later.
• "Off": VPA does not automatically change resource requirements of the pods. The recommendations are calculated and can be inspected in the VPA object.

Test your installation

A simple way to check if Vertical Pod Autoscaler is fully operational in your cluster is to create a sample deployment and a corresponding VPA config:

kubectl create -f examples/hamster.yaml

The above command creates a deployment with 2 pods, each running a single container that requests 100 millicores and tries to utilize slightly above 500 millicores. The command also creates a VPA config with selector that matches the pods in the deployment. VPA will observe the behavior of the pods and after about 5 minutes they should get updated with a higher CPU request (note that VPA does not modify the template in the deployment, but the actual requests of the pods are updated). To see VPA config and current recommended resource requests run:

kubectl describe vpa

Note: if your cluster has little free capacity these pods may be unable to schedule. You may need to add more nodes or adjust examples/hamster.yaml to use less CPU.

Example VPA configuration

apiVersion: poc.autoscaling.k8s.io/v1alpha1
kind: VerticalPodAutoscaler
metadata:
  name: my-app-vpa
spec:
  selector:
    matchLabels:
      app: my-app
  updatePolicy:
    updateMode: "Auto"

Troubleshooting

To diagnose problems with a VPA installation, perform the following steps:

• Check if all system components are running:

kubectl --namespace=kube-system get pods|grep vpa

The above command should list 3 pods (recommender, updater and admission-controller) all in state Running.

• Check if the system components log any errors. For each of the pods returned by the previous command do:

kubectl --namespace=kube-system logs [pod name]| grep -e '^E[0-9]\{4\}'

• Check that the VPA Custom Resource Definition was created:

kubectl get customresourcedefinition|grep verticalpodautoscalers

Components of VPA

The project consists of 3 components:

• Recommender - it monitors the current and past resource consumption and, based on it, provides recommended values containers' cpu and memory requests.

• Updater - it checks which of the managed pods have correct resources set and, if not, kills them so that they can be recreated by their controllers with the updated requests.

• Admission Plugin - it sets the correct resource requests on new pods (either just created or recreated by their controller due to Updater's activity).

More on the architecture can be found HERE.

Tear down

Note that if you stop running VPA in your cluster, the resource requests for the pods already modified by VPA will not change, but any new pods will get resources as defined in your controllers (i.e. deployment or replicaset) and not according to previous recommendations made by VPA.

To stop using Vertical Pod Autoscaling in your cluster:

• If runnning on GKE, clean up role bindings created in Prerequisites:

kubectl delete clusterrolebinding myname-cluster-admin-binding

• Tear down VPA components:

./hack/vpa-down.sh

Known limitations of the alpha version

• Whenever VPA updates the pod resources the pod is recreated, which causes all running containers to be restarted.
• Vertical Pod Autoscaler is not fully compatible with the Horizontal Pod Autoscaler at this moment. You should either use one or the other, depending on which one is more suitable to a specific workload.
• VPA in auto mode can only be used on pods that run under a controller (such as Deployment), which is responsible for restarting deleted pods. Using VPA in auto mode with a pod not running under any controller will cause the pod to be deleted and not recreated.
• The VPA admission controller is an admission webhook. If you add other admission webhooks to you cluster, it is important to analyze how they interact and whether they may conflict with each other. The order of admission controllers is defined by a flag on APIserver.
• VPA reacts to some out-of-memory events, but not in all situations.
• VPA performance has not been tested in large clusters.
• VPA recommendation might exceed available resources (e.g. Node size, available size, available quota) and cause pods to go pending. This can be addressed by using VPA together with Cluster Autoscaler.
• Multiple VPA resources matching the same pod have undefined behavior.

Related links

• Design proposal
• API definition