As pods move around between nodes, applications are updated, etc., nodes
tend to accumulate images in their container stores that are no longer
used. These take up space unnecessarily, eventually triggering disk
usage alarms. From now, the _kubelet_ role installs a systemd timer and
service unit to periodically clean up these unused images.
The systemd unit configuration installed by Fedora's _kubeadm_ package
does not pass the `--config` argument to the kubelet service. Without
this argument, the kubelet will not read the configuration file
generated by `kubeadm` from the `kubelet-config` ConfigMap. Thus,
various features will not work correctly, including server TLS
bootstrap.
So far, I have been managing Kubernetes worker nodes with Fedora CoreOS
Ignition, but I have decided to move everything back to Fedora and
Ansible. I like the idea of an immutable operating system, but the FCOS
implementation is not really what I want. I like the automated updates,
but that can be accomplished with _dnf-automatic_. I do _not_ like
giving up control of when to upgrade to the next Fedora release.
Mostly, I never did come up with a good way to manage application-level
configuration on FCOS machines. None of my experiments (Cue+tmpl,
KCL+etcd+Luci) were successful, which mostly resulted in my manually
managing configuration on nodes individually. Managing OS-level
configuration is also rather cumbersome, since it requires redeploying
the machine entirely. Altogether, I just don't think FCOS fits with my
model of managing systems.
This commit introduces a new playbook, `kubernetes.yml`, and a handful of
new roles to manage Kubernetes worker nodes running Fedora Linux. It
also adds two new deploy scripts, `k8s-worker.sh` and `k8s-longhorn.sh`,
which fully automate the process of bringing up worker nodes.
