doc: write how to use kata-container for pods (#8817 )

kata-container is not used by default even if enabling kata_containers_enabled.
This updates the doc for writing how to do that.

2022-05-13 23:15:18 -07:00

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Kata Containers

Kata Containers is a secure container runtime with lightweight virtual machines that supports multiple hypervisor solutions.

Hypervisors

Qemu is the only hypervisor supported by Kubespray.

Installation

To enable Kata Containers, set the following variables:

k8s-cluster.yml:

container_manager: containerd
kata_containers_enabled: true

etcd.yml:

etcd_deployment_type: host

Usage

By default, runc is used for pods. Kubespray generates the runtimeClass kata-qemu, and it is necessary to specify it as the runtimeClassName of a pod spec to use Kata Containers:

$ kubectl get runtimeclass
NAME        HANDLER     AGE
kata-qemu   kata-qemu   3m34s
$
$ cat nginx.yaml
apiVersion: v1
kind: Pod
metadata:
  name: mypod
spec:
  runtimeClassName: kata-qemu
  containers:
  - name: nginx
    image: nginx:1.14.2
$
$ kubectl apply -f nginx.yaml

Configuration

Recommended : Pod Overhead

Pod Overhead is a feature for accounting for the resources consumed by the Runtime Class used by the Pod.

When this feature is enabled, Kubernetes will count the fixed amount of CPU and memory set in the configuration as used by the virtual machine and not by the containers running in the Pod.

Pod Overhead is mandatory if you run Pods with Kata Containers that use resources limits.

Set cgroup driver:

To enable Pod Overhead feature you have to configure Kubelet with the appropriate cgroup driver, using the following configuration:

cgroupfs works best:

kubelet_cgroup_driver: cgroupfs

... but when using cgroups v2 (see https://www.redhat.com/en/blog/world-domination-cgroups-rhel-8-welcome-cgroups-v2) you can use systemd as well:

kubelet_cgroup_driver: systemd

Qemu hypervisor configuration:

The configuration for the Qemu hypervisor uses the following values:

kata_containers_qemu_overhead: true
kata_containers_qemu_overhead_fixed_cpu: 10m
kata_containers_qemu_overhead_fixed_memory: 290Mi

Optional : Select Kata Containers version

Optionally you can select the Kata Containers release version to be installed. The available releases are published in GitHub.

kata_containers_version: 2.2.2

Optional : Debug

Debug is disabled by default for all the components of Kata Containers. You can change this behaviour with the following configuration:

kata_containers_qemu_debug: 'false'

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