Add Cluster AutoScaler as an Addon

[christopherhein]

Needs to add the following policy to the instance role:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "autoscaling:DescribeAutoScalingGroups",
                "autoscaling:DescribeAutoScalingInstances",
                "autoscaling:SetDesiredCapacity",
                "autoscaling:TerminateInstanceInAutoScalingGroup"
            ],
            "Resource": "*"
        }
    ]
}

Apply the CA manifest file with the autoscaling group prefilled.

[errordeveloper]

I think we should be able to cater for this very easily once #132 lands. So we can add IAM role changes (perhaps as a flag) in 0.1.x (and document usage), and then implement actual add-on in 0.2.x, when we have proper way of managing add-ons.

[mumoshu]

As similar as I wrote in #242 (comment), I'm personally fine as long as eksctl adds necessary IAM perms to the role.

Based on my experience in kube-aws, users occasionally wanted to update just a subset of installed addons, like in this case just adding a flag to cluster-autoscaler. Also, some people wanted to uninstall CA installed by kube-aws and rather use helm or their own manifest for further management.

So for the former case, running eksctl just for updating a single addon would be just cumbersome. For the latter case installing CA via an addon seems redundant.

[michaelbeaumont]

The IAM permissions are now available with iamConfig.WithAddonPolicies.AutoScaler. Seems like consensus is that the autoscaler addon itself doesn't need to be part of eksctl