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typhoon/docs/architecture/operating-systems.md
Dalton Hubble eda78db08e Change Flatcar kubelet.service container from rkt to docker 
* Use docker to run the `kubelet.service` container
* Update Kubelet mounts to match Fedora CoreOS
* Remove unused `/etc/ssl/certs` mount (see
https://github.com/poseidon/typhoon/pull/810)
* Remove unused `/usr/share/ca-certificates` mount
* Remove `/etc/resolv.conf` mount, Docker default is ok
* Change `delete-node.service` to use docker instead of rkt
and inline ExecStart, as was done on Fedora CoreOS
* Fix permission denied on shutdown `delete-node`, caused
by the kubeconfig mount changing with the introduction of
node TLS bootstrap

Background

* podmand, rkt, and runc daemonless container process runners
provide advantages over the docker daemon for system containers.
Docker requires workarounds for use in systemd units where the
ExecStart must tail logs so systemd can monitor the daemonized
container. https://github.com/moby/moby/issues/6791
* Why switch then? On Flatcar Linux, podman isn't shipped. rkt
works, but isn't developing while container standards continue
to move forward. Typhoon has used runc for the Kubelet runner
before in Fedora Atomic, but its more low-level. So we're left
with Docker, which is less than ideal, but shipped in Flatcar
* Flatcar Linux appears to be shifting system components to
use docker, which does provide some limited guards against
breakages (e.g. Flatcar cannot enable docker live restore)
2020-10-18 23:24:45 -07:00

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Operating Systems

Typhoon supports Fedora CoreOS and Flatcar Linux. These operating systems were chosen because they offer:

  • Minimalism and focus on clustered operation
  • Automated and atomic operating system upgrades
  • Declarative and immutable configuration
  • Optimization for containerized applications

Together, they diversify Typhoon to support a range of container technologies.

  • Fedora CoreOS: rpm-ostree, podman, moby
  • Flatcar Linux: Gentoo core, rkt-fly, docker

Host Properties

Property Flatcar Linux Fedora CoreOS
Kernel ~5.4.x ~5.8.x
systemd 245 245
Ignition system Ignition v2.x spec Ignition v3.x spec
Container Engine docker 19.3.12 docker 19.03.11
storage driver overlay2 (extfs) overlay2 (xfs)
logging driver json-file journald
cgroup driver cgroupfs (except Flatcar edge) systemd
Networking systemd-networkd NetworkManager
Username core core

Kubernetes Properties

Property Flatcar Linux Fedora CoreOS
single-master all platforms all platforms
multi-master all platforms all platforms
control plane static pods static pods
kubelet image kubelet image with upstream binary kubelet image with upstream binary
control plane images upstream images upstream images
on-host etcd rkt-fly podman
on-host kubelet docker podman
CNI plugins calico, cilium, flannel calico, cilium, flannel
coordinated drain & OS update FLUO addon fleetlock

Directory Locations

Typhoon conventional directories.

Kubelet setting Host location
cni-conf-dir /etc/kubernetes/cni/net.d
pod-manifest-path /etc/kubernetes/manifests
volume-plugin-dir /var/lib/kubelet/volumeplugins