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setup/cri: add a section about cgroup drivers #12638

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Feb 18, 2019
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setup/cri: add a section about cgroup drivers #12638

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setup/cri: add a section about cgroup drivers
neolit123 Feb 14, 2019
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Update cri.md
zparnold Feb 17, 2019
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20 changes: 19 additions & 1 deletion content/en/docs/setup/cri.md
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Expand Up @@ -26,6 +26,24 @@ Please refer to this link for more information about this issue
[cve-2019-5736 : runc vulnerability ] (https://access.redhat.com/security/cve/cve-2019-5736)
{{< /caution >}}

## Cgroup drivers

When systemd is chosen as the init system for a Linux distribution, the init process generates
and consumes a root cgroup and acts as a cgroup manager. Systemd has a tight integration with
cgroups and will allocate cgroups per process. It's possible to configure your container
runtime and the kubelet to use `cgroupfs`. This means that there will then be two different
cgroup managers.

Cgroups are used to constrain resources that are allocated to processes.
A single cgroup manager will simplify the view of what resources are being allocated
and will by default have a more consistent view of the available and in-use resources. When we have
two managers we end up with two views of those resources. We have seen cases in the field
where nodes that are configured to use `cgroupfs` for the kubelet and Docker, and `systemd`
for the rest of the processes running on the node becomes unstable under resource pressure.

Changing the settings such that your container runtime and kubelet use `systemd` as the cgroup driver
stabilized the system. Please note the `native.cgroupdriver=systemd` option in the Docker setup below.

## Docker

On each of your machines, install Docker.
Expand Down Expand Up @@ -59,7 +77,7 @@ apt-get update && apt-get install docker-ce=18.06.2~ce~3-0~ubuntu
# Setup daemon.
cat > /etc/docker/daemon.json <<EOF
{
"exec-opts": ["native.cgroupdriver=cgroupfs"],
"exec-opts": ["native.cgroupdriver=systemd"],
"log-driver": "json-file",
"log-opts": {
"max-size": "100m"
Expand Down