init System to ContainersTL;DR: mount -v /sys/fs/cgroup:/sys/fs/cgroup:ro so that your apt
install systemd work. You must have systemd installed on Ubuntu for
kubeadm to work which is what all major Linux distro supporting
Kubernetes require (Ubuntu, Red Hat, SUSE).
I’m still relatively new to creating my own images, but I’ve been
fascinated by how most images don’t have an init system of any kind.
PID 1 is always bash or something. When working with use cases where
you need to simulate an actual host machine (which I call a host
container or workspace container) then you really do. But do you
really need to bring the big, ugly, bloated systemd piece of shit into
your container to model a host OS?
The answer is no. But there are a lot of options to pick from. Narrowing
it down has been non-trivial. Not all init systems are created equal,
and many are simply not detected by things like kubeadm as sufficient. Here is a list I’ll maintain as I uncover different alternative options and test them:
openrcsysvinitupstarttinirunitnoshfinitSince I’m almost always doing this for Kubernetes related work for me
the choice became obvious once I read through the kubeadm source code
to figure out which “init systems” are supported. systemd and openrc
are the only options, and since they pulled openrc support from Ubuntu
the answer is forced on us: get systemd to work (which is not trivial,
unfortunately).
// GetInitSystem returns an InitSystem for the current system, or nil
// if we cannot detect a supported init system.
// This indicates we will skip init system checks, not an error.
func GetInitSystem() (InitSystem, error) {
// Assume existence of systemctl in path implies this is a systemd system:
_, err := exec.LookPath("systemctl")
if err == nil {
return &SystemdInitSystem{}, nil
}
_, err = exec.LookPath("openrc")
if err == nil {
return &OpenRCInitSystem{}, nil
}
return nil, fmt.Errorf("no supported init system detected, skipping checking for services")
}
⚠️ Be sure to disambiguate your search for “init systems” from “init containers” which are an entirely different thing in Kubernetes.
Related:
Tags:
#k8s #docker #init #systemd