I know many services provided a managed control plane. GKE, Digital Ocean. I want a Kubernetes cluster using those service as they provide reliablity. But I want to expand my kubernetes cluster using a number of physical machines, old machines, raspberry pis etc that I have in my local office.

Is it possible? If so, how can I do that?

I found two questions in stackoverflow related to this, but both go with unsatisfactory answers

• Add external node to GCP Kubernetes Cluster

Here the answer seems to be using kubeadm init - which really is not about adding a worker node, but doing making the control plane HA.

• GKE with Aws worker nodes

Says it is possible, but does not mention how to add external worker nodes.