What's the difference between cgroupfs and systemd ?

palarun

Wanted to understand the difference between cgroupfs and systemd ?
Which control group is default, why docker use cgoupfs as there default control group and why kubernetes is telling us to run docker in systemd

fcioanca

@palarun Is this question related to LFS258 course?

palarun

Yes , it is.

leopastorsdg

This question is more related to Linux, OS, systems and software engineering, compatibility, etc

@palarun While it is beyond the scope of this course, the excerpts below might give you an idea on the reasons why to use "systemd" when using Docker as a container runtime engine.

"
Using cgroupfs alongside systemd means that there will be two different cgroup managers.
...
When there are two cgroup managers on a system, you end up with two views of those resources.
... cases where nodes that are configured to use cgroupfs for the kubelet and Docker, but systemd for the rest of the processes, become unstable under resource pressure.
"
The above is taken from Cgroup drivers.

If Docker with cgroupfs drivers is configured, kubeadm init detects it when running some pre-flight checks and generates a warning. That can be seen in some outputs shown in Lab 3.1 Install Kubernetes.

HTH