What is a Node?

A Node is a machine; a Node is where the Pods are running. But under the hood, what is a Node?

A Node could be a bare-metal machine

You need to either manually provision the bare-metal machine, or use some automation tools like Ansible, Ironic, Metal3. Then a container runtime (e.g. containerd) runs Pod/containers on the bare-metal machine.

A Node could be a virtual machine

• could be VMs running on your own bare-metals
• could be VMs running inside your own VMs
• could be cloud VMs, like a AWS EC2 instance or a Google Compute Engine instance.

A Node could be a container

Yes a Node can be a container. If you use kind to create a cluster, each node is a docker container (kind = Kubernetes IN Docker). If you use minikube, you can also choose to use containers as nodes.

A nested world

If you use GKE:

• Borg (Google's internal cluster management system) runs the backend of GKE/GCE APIs
• GCE API creates VMs on Borg Nodes.
  • "We run each hosted VM in a KVM process that runs as a Borg task." https://research.google/pubs/pub43438/
• GKE API manages clusters using GCE VMs.
• Your Pods are running on GCE VMs.

If you use kind on a Cloud VM:

• your Pods (managed by containerd) are running in a container (managed by Docker)
• the Docker container is running on a VM.
• The VM is running on a Cloud provider's bare-metal machines.