Deploy The Node Termination Handler

When users requests On-Demand instances from a pool to the point that the pool is depleted, the system will select a set of spot instances from the pool to be terminated. A Spot instance pool is a set of unused EC2 instances with the same instance type (for example, m5.large), operating system, Availability Zone, and network platform. The Spot Instance is sent an interruption notice two minutes ahead to gracefully wrap up things.

We will deploy a pod on each spot instance to detect the instance termination notification signal so that we can both terminate gracefully any pod that was running on that node, drain from load balancers and redeploy applications elsewhere in the cluster.

AWS Node Termination Handler does far more than just capture EC2 Spot Instance notification for terminations. There are other events such as Scheduled Maintenance Events that are taken into consideration. AWS Node Termination handler does also offer a Webhook that can be used to integrate with other applications to monitor and instrument this events. You can find more information about AWS Node Termination Handler following this link

The Helm chart we will use to deploy AWS Node Termination Handler on each Spot Instance uses a DaemonSet. This will monitor the EC2 meta-data service on each of the EC2 Spot instances to capture EC2 interruption notices.

Within the Node Termination Handler DaemonSet, the workflow can be summarized as:

  • Identify that a Spot Instance is being reclaimed.
  • Use the 2-minute notification window to gracefully prepare the node for termination.
  • Taint the node and cordon it off to prevent new pods from being placed.
  • Drain connections on the running pods.
  • Replace the pods on remaining nodes to maintain the desired capacity.

By default, aws-node-termination-handler will run on all of your nodes (on-demand and spot). If your spot instances are labeled, you can configure aws-node-termination-handler to only run on your labeled spot nodes. If you’re using the tag lifecycle=Ec2Spot, you can run the following to apply our spot-node-selector overlay.

helm repo add eks https://aws.github.io/eks-charts
helm install --name aws-node-termination-handler \
             --namespace kube-system \
             --set nodeSelector.lifecycle=Ec2Spot \
             eks/aws-node-termination-handler

Verify that the pods are only running on node with label lifecycle=Ec2Spot

kubectl get daemonsets --all-namespaces

Use kube-ops-view to confirm AWS Node Termination Handler DaemonSet has been deployed only to EC2 Spot nodes.

Although in this workshop we deployed the AWS Node Termination Handler only to EC2 Spot nodes, our recommendation is to run the AWS Node Termination handler also on nodes where you would like to capture other termination events such as maintenance events or in the future Auto Scaling AZ Balancing events