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Auto scaling of a group of nodes
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Auto scaling of a group of nodes

For your information

Auto Zoom is not available:

  • for groups of nodes with GPUs without drivers;
  • groups of nodes on dedicated servers.

In a Managed Kubernetes cluster on a cloud server, node groups are autoscaled using Cluster Autoscaler. It helps to optimally utilize cluster resources — depending on the load on the cluster, the number of nodes in the group will automatically decrease or increase.

You do not need to install Cluster Autoscaler in the cluster.

You can enable autoscaling of a group of nodes can be enabled in the control panel, via API Managed Kubernetes or through Terraform.

Managed Kubernetes uses Metrics Server to autoscale pods.

Principle of operation⁠

The minimum and maximum number of nodes in a group can be set when autoscaling is enabled — Cluster Autoscaler will only change the number of nodes within these limits.

If a group of nodes is in ACTIVE status, Cluster Autoscaler checks every 10 seconds if there are Pods in PENDING status and analyzes the load — requests from Pods on vCPU, RAM and GPU. Depending on the results of the check, nodes are added or removed. A group of nodes at this time goes to the PENDING_SCALE_UP or PENDING_SCALE_DOWN status . The status of the cluster during autoscaling is ACTIVE.

Learn more about cluster statuses in the instructions View Cluster Status.

Adding a node⁠

If there are pods in the PENDING status and the cluster does not have enough free resources to accommodate them, the necessary number of nodes will be added to the cluster. In a cluster with Kubernetes version 1.28 and higher, Cluster Autoscaler will work in several groups at once and distribute nodes evenly.

note

For example, you have two groups of nodes with autoscaling enabled. The load on the cluster has increased and requires the addition of four nodes. Two new nodes will be created in each node group at the same time.

In a cluster with Kubernetes version 1.27 and below, nodes are added one per validation cycle.

Deleting a node⁠

If there are no pods in PENDING status, Cluster Autoscaler checks the number of resources that are requesting pods.

If the total number of resources requested by pods on a node is less than 50% of its resources, Cluster Autoscaler marks the node as unnecessary. If the number of resource requests on a node does not increase after 10 minutes, Cluster Autoscaler will check if pods can be moved to other nodes.

Cluster Autoscaler will not migrate pods and therefore will not delete a node if one of the conditions is met:

  • Pods use PodDisruptionBudget;
  • there is no PodDisrptionBudget in Kube-system pods;
  • pods are created without a controller — for example, Deployment, ReplicaSet, StatefulSet;
  • Pods use local storage;
  • the other nodes don't have the resources for the pod's requests;
  • there is a mismatch of nodeSelector, affinity/anti-affinity rules or other parameters.

You can allow such submissions to carry over — add an annotation to do so:

cluster-autoscaler.kubernetes.io/safe-to-evict: "true"

If there are no restrictions, pods will be moved and low-loaded nodes will be removed. Nodes are removed one at a time per test cycle.

Recommendations⁠

For optimal performance of Cluster Autoscaler, we recommend:

  • make sure that the project has quotas for vCPU, RAM, GPU and disk capacity to create the maximum number of nodes in the group;
  • specify resource requests in the manifests for pods;
  • check that nodes in the group have the same configuration and labels;
  • configure PodDisruptionBudget for pods for which no stoppages are allowed. This will help to avoid downtime when transferring between nodes;
  • do not use any other Cluster Autoscaler;
  • do not manually modify node resources through the control panel. Cluster Autoscaler will ignore these changes and all new nodes will be created with the original configuration.

Enable autoscaling⁠

For your information

If you set the minimum number of nodes in the group to be greater than the current number, it will not scale to the lower limit immediately. The group of nodes will be scaled only after the pods appear in the PENDING status. The same with the upper limit of nodes in the group — if the current number of nodes is greater than the upper limit, deletion will start only after the pods are checked.

  1. In the dashboard, on the top menu, click Products and select Managed Kubernetes.
  2. Open the Cluster page → Cluster Composition tab.
  3. From the menu of the node group, select Change Number of Nodes.
  4. In the Number of nodes field, open the With autoscaling tab.
  5. Set the minimum and maximum number of nodes in the group — the value of nodes will change only within this range. For fault-tolerant operation of system components we recommend using at least two working nodes in the cluster, nodes can be in different groups.
  6. Click Save.