sh4d1 / vks

Virtual Kubelet Provider for Systemd

NOTE: Work In Progress

Virtual Kubelet for systemd

This is an virtual kubelet provider that interacts with systemd. The aim is to make this to work with K3S and go from there.

vks will start pods as plain processes, there are no cgroups (yet, maybe systemd will allow for this easily), but generally there is no isolation. You basically use the k8s control plane to start linux processes. There is also no address space allocated to the PODs specically, you are using the host's networking.

"Images" are referencing (Debian) packages, these will be apt-get installed. Discoverying that an installed package is no longer used is hard, so this will not be done.

Each scheduled unit will adhere to a nameing scheme so vks knows which ones are managed by it.

Questions

• Pods can contain multiple containers. In systemd each container is a Unit (file). How can we keep track of these diff. Units and re-create the Pod when we need to?
• Pod storage, secret etc. Just something on disk? /var/lib/<something>?
• How to provision a Debian system to be able to join a k3s cluster? Something very minimal is needed here. Maybe getting to k3s super early will help. We can then install extra things to configure?
• Add a private repo for debian packages. I.e. I want to install latest CoreDNS which isn't in Debian. I need to add a repo for this... How?
• If imagePullPolicy is set to Always, then apt-get install the binary ? If not check if the "image" can be found in $PATH and use it?
• namespaces?? Are they useful on a technical level for systemd?

Use with K3S

Download k3s from it's releases on GitHub, you just need the k3s binary. Use the k3s/k3s shell script to start it - this assumes k3s sits in "~/tmp/k3s". The script basically starts k3s with basically everything disabled.

Compile cmd/virtual-kubelet and start it with:

./cmd/virtual-kubelet/virtual-kubelet --kubeconfig ~/.rancher/k3s/server/cred/admin.kubeconfig \
--enable-node-lease --disable-taint

Now a k3s kubcetl get nodes should show the virtual kubelet as a node:

NAME    STATUS   ROLES   AGE   VERSION   INTERNAL-IP   EXTERNAL-IP   OS-IMAGE            KERNEL-VERSION     CONTAINER-RUNTIME
draak   Ready    agent   6s    v1.18.4   <none>        <none>        Ubuntu 20.04.1 LT   5.4.0-53-generic   systemd 245 (245.4-4ubuntu3.3)

draak is my machine's name.

You can now try to schedule a pod: k3s/kubelet apply -f k3s/openssh-server.yaml. This will call out and try to schedule.