Spot Instances use and management for Kubernetes

The minion-manager enables the intelligent use of Spot Instances in Kubernetes.

What does it do?

• The minion-manager operates on autoscaling groups (ASGs).

• It queries AWS for all autoscaling groups that have the Kubernetes cluster tag and a special tag called "k8s-minion-manager". ASGs which have these tags are operated upon by the minion-manager.

• It queries AWS to get the pricing information for spot-instances every 10 minutes.

• It checks whether the given ASGs are using spot-instances or on-demand instances. If the spot-instance price < on-demand instance price, it switches the ASG to use spot-instances and terminates the on-demand instance.

• If, at any point in time, the spot-instance price spikes and goes above on-demand instance price, it switches the ASG to use on-demand instances.

Prerequisites

It's best to run the minion-manger on an on-demand instance.

The IAM role of the node that runs the minion-manager should have the following policies.

{
    "Sid": "kopsK8sMinionManager",
    "Effect": "Allow",
    "Action": [
	"ec2:DescribeInstances",
	"ec2:TerminateInstances",
	"ec2:DescribeSpotPriceHistory",
	"autoscaling:CreateLaunchConfiguration",
	"autoscaling:DeleteLaunchConfiguration",
	"autoscaling:DescribeLaunchConfigurations",
        "autoscaling:DescribeAutoScalingGroups",
        "autoscaling:TerminateInstanceInAutoScalingGroup",
        "autoscaling:UpdateAutoScalingGroup",
	"iam:PassRole"
    ],
    "Resource": [
	"*"
    ]
}

Installing

Modify the deploy/mm.yaml by

1. Add the names of your cluster instead of
2. Change the namespace where the minion-manager will be run.

Then, kubectl apply -f deploy/mm.yaml.

Design:

• Only ASGs which have the "k8s-minion-manager" tag are considered by the minion-manager. Other ASGs are left alone.
• Minion-manager queries AWS for ASGs with these tags every "--refresh-interval". Default is 5 minutes.
• The "k8s-minion-manager" tag can have two possible values:
  • "use-spot": This will make the minion-manager intelligently use spot instances in the ASG
  • "no-spot": This will make the minion-manager always use on-demand instances in the ASG. This is useful when someone wants to temporarily switch to on-demand instances and at a later point switch to "use-spot"
  • Note that after changing the tag value, it may take upto 5 minutes for the minion-manager pod to see the changes and make them take effect.

What happens when:

1. User runs k8s-minion-manager without any ASG having the "k8s-minion-manager" tag?

k8s-minion-manager ignores all ASGs. It simply continues to keep polling AWS for the tags every "refresh-interval" seconds.

2. User runs k8s-minion-manager, adds the "k8s-minion-manager" tag and the "use-spot" value to start with. But later wants to not use spot instances.

User should then change the key from "use-spot" to "no-spot". This will indicate to the k8s-minion-manager that the ASG should have all on-demand instances and it will make sure of that.

3. User runs k8s-minion-manager, adds the "k8s-minion-manager" key and the "use-spot" value to start with. But later simply removes the tag and the value.

Once the tag is removed, k8s-minion-manager simply considers the ASG to be off-limits and does not act upon it. The ASG will remain in whatever condition it is in.

4. User runs k8s-minion-manager, adds the "k8s-minion-manager" key and the "no-spot" value to start with. But later simply removes the tag and the value.

Same as above. The ASG will remain in whatever condition it is in.

5. User is running k8s-minion-manager and using spot instances. But now wants to stop using instances forever.

This will be a multi-step process:

• Change the value of the "k8-minion-manager" tag to "no-spot".
• Wait for the minion-manager to react to this and switch the instances to on-demand. Look at the AWS console for verifying that all instances are on-demand.
• After the above, remove the "k8s-minion-manager" tag.
• Delete the "k8s-minion-manager" deployment.