In k3s today the kubernetes API and the /v1-k3s API are combined into
one http server. In rke2 we are running unmodified, non-embedded Kubernetes
and as such it is preferred to run k8s and the /v1-k3s API on different
ports. The /v1-k3s API port is called the SupervisorPort in the code.
To support this separation of ports a new shim was added on the client in
then pkg/agent/proxy package that will launch two load balancers instead
of just one load balancer. One load balancer for 6443 and the other
for 9345 (which is the supervisor port).
Values passed in via the server/agent `--node-label` flag are treated as mutable. They are passed through to the kubelet just as before but after the kubelet comes up they are applied again. This allows for passing labels a k3s start-time that may be necessary for scheduling but may change from boot to boot, e.g. `k3os.io/version` after an upgrade.
Tested locallon on my amd64 workstation with the docker container.
Addresses #1119.
