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 ensures that the Kubernetes control plane responds appropriately to events that can cause your EC2 instance to become unavailable, such as EC2 maintenance events, EC2 Spot interruptions, ASG Scale-In, ASG AZ Rebalance, and EC2 Instance Termination via the API or Console. If not handled, your application code may not stop gracefully, take longer to recover full availability, or accidentally schedule work to nodes that are going down.
The aws-node-termination-handler (NTH) can operate in two different modes: Instance Metadata Service (IMDS) or the Queue Processor.
|Syntax||IMDS Processor||Queue Processor|
|Spot Instance Interruptions (ITN)||✅||✅|
|EC2 Instance Rebalance Recommendation||✅||✅|
|ASG Lifecycle Hooks||❌||✅|
|EC2 Status Changes||❌||✅|
To keep it simple, we will use Helm chart to deploy aws-node-termination-handler in IMDS mode on each Spot Instance as a DaemonSet. Within the aws-node-termination-handler in IMDS mode, the workflow can be summarized as:
By default, aws-node-termination-handler will run on all of your nodes. Let’s limit it’s scope to only self managed node groups with Spot Instances.
helm repo add eks https://aws.github.io/eks-charts helm install aws-node-termination-handler \ --namespace kube-system \ --version 0.15.4 \ --set nodeSelector.type=self-managed-spot \ eks/aws-node-termination-handler
Verify that the pods are running on all nodes:
kubectl get daemonsets --all-namespaces
Use kube-ops-view to confirm AWS Node Termination Handler DaemonSet has been deployed to all nodes.