Introduction to cri-o and crictl

Setup

Install cri-o

• To install cri-o in CentOS 8 run the following commands. If using another distribution check in the cri-o repository for instructions on how to install.

VERSION=1.19

OS=CentOS_8

sudo curl -L -o /etc/yum.repos.d/devel:kubic:libcontainers:stable.repo https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable/$OS/devel:kubic:libcontainers:stable.repo

sudo curl -L -o /etc/yum.repos.d/devel:kubic:libcontainers:stable:cri-o:$VERSION.repo https://download.opensuse.org/repositories/devel:kubic:libcontainers:stable:cri-o:$VERSION/$OS/devel:kubic:libcontainers:stable:cri-o:$VERSION.repo

sudo yum install cri-o

• After cri-o is installed we can enable and start the service.

sudo systemctl enable crio
sudo systemctl start crio
sudo systemctl status crio

Install crictl

• To install crictl run the following commands.

sudo curl -LO https://github.com/kubernetes-sigs/cri-tools/releases/download/v1.19.0/crictl-v1.19.0-linux-amd64.tar.gz

sudo tar -zxvf crictl-v1.19.0-linux-amd64.tar.gz -C /usr/bin

rm -f crictl-v1.19.0-linux-amd64.tar.gz

• Check everything was installed succesfully by running the following commands

sudo crictl version
crio version

• Use the info command to get information about the container runtime

sudo crictl info

Considerations for this demo

• The cri-o container runtime is an implementation of the kubernetes CRI and as such it only has the functions defined in the interface.

• crictl is a debugging tool for the CRI. It is not supposed to be used to run containers or pods but it is capable of doing so.

• Using crictl to create a container is useful for debugging container runtimes. On a running Kubernetes cluster, the sandbox/pod will eventually be stopped and deleted by the Kubelet.

• In this demo we are creating pods and containers using crictl but in reality when running in a kubernetes cluster those actions will be done by the kubelet and after configuring cri-o as the container runtime for the cluster there is no need to use it directly.

• Crictl can interact with any CRI compliant container runtime such as containerd, cri-o and docker (dockershim).