It is expected behavior because kubespray doesn't create any ASGs, which are AWS-specific resources. One will observe that kubespray only deals with existing machines; they do offer some terraform toys in their repo for provisioning machines, but kubespray itself does not get into that business.

You have a few options available to you:

Post-provision using scale.yml

1. Provision the new Node using your favorite mechanism
2. Create an inventory file containing it, and the etcd machines (presumably so kubespray can issue etcd certificates for the new Node
3. Invoke the scale.yml playbook

You may enjoy AWX in support of that.

Using plain kubeadm join

This is the mechanism I use for my clusters, FWIW

1. Create a kubeadm join token using kubeadm token create --ttl 0 (or whatever TTL you feel comfortable using)

   You'll only need to do this once, or perhaps once per ASG, depending on your security tolerances

2. Use the cloud-init mechanism to ensure that docker, kubeadm, and kubelet binaries are present on the machine

   You are welcome to use an AMI for doing that, too, if you enjoy building AMIs

3. Then invoke kubeadm join as described here: https://kubernetes.io/docs/setup/independent/high-availability/#install-workers

Use a Machine Controller

There are plenty of "machine controller" components that aim to use custom controllers inside Kubernetes to manage your node pools declaratively. I don't have experience with them, but I believe they do work. That link was just the first one that came to mind, but there are others, too

Our friends over at Kubedex have an entire page devoted to this question