Container Runtime Interface

Install CRI-O (Container Runtime) 

CRI-O is an implementation of the Kubernetes CRI (Container Runtime Interface) to enable using OCI (Open Container Initiative) compatible runtimes.

runc:

runc is a low-level container runtime that directly interacts with the Linux kernel to create and run containers.

runc provides the basic functionality for creating and running containers, while containerd provides a more complete environment for managing and orchestrating container workloads.

ctr is unsupported debug and administrative client for interacting with the containerd daemon.

Because it is unsupported, the commands,options, and operations are not guaranteed to be backward compatible or stable from release to release of the containerd project.

Linux OS -> runc -> CRI

https://github.com/cri-o/cri-o/releases

https://github.com/opencontainers/runtime-tools

https://github.com/kubernetes-sigs/cri-tools/releases

# dnf install container-selinux cri-o cri-tools

# systemctl enable --now crio

Socket File

/var/run/crio/crio.sock 

Install Containerd

Containerd is an open-source CRI (Container Runtime Interface) compatible container runtime. It is created by Docker and donated to CNCF.

# dnf install -y yum-utils

# dnf config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo

# dnf install -y containerd.io

Generate a default configuration file for Containerd, and then we need to modify it as needed 

SystemdCgroup to true 

# mkdir -p /etc/containerd

# containerd config default > /etc/containerd/config.toml

Edit /etc/containerd/config.toml if necessary, for example:

# sed -i 's/SystemdCgroup = false/SystemdCgroup = true/g' /etc/containerd/config.toml

# systemctl enable --now containerd

Socket File
var/run/containerd/containerd.sock

Install cri-tools

# curl -L https://github.com/kubernetes-sigs/cri-tools/releases/download/$VERSION/crictl-${VERSION}-linux-${ARCH}.tar.gz --output crictl-${VERSION}-linux-${ARCH}.tar.gz

Extract the downloaded archive and move the crictl binary to a directory within your system's PATH, such as /usr/local/bin/

# tar zxvf crictl-${VERSION}-linux-${ARCH}.tar.gz -C /usr/local/bin

# crictl --version

# crictl info

# crictl info | grep -i containerd

Pull Image

# crictl pull  hello-world:latest

# crictl pull  alpine:latest

List container images 

# crictl images

# crictl images nginx

# crictl images -q # List Image Ids

List all containers:

# crictl ps -a

# crictl ps # List Running Containers

Execute a command in a running container

# crictl exec -i -t <Container-ID> ls

Get Container Logs

# crictl logs <Container-ID>

# crictl logs --tail=1 <Container-ID>

# crictl stop <Container-ID>

# crictl stats <Container-ID>

# crictl inspect <Container-ID>

# crictl rm 

List Pod resourse usage statistics

# crictl statsp <Container-ID>

To set container registries and set priority, edit the file:

# vi /etc/containers/registries.conf

eg 

unqualified-search-registries = ["registry.fedoraproject.org", "registry.access.redhat.com", "registry.centos.org", "docker.io"]

List pods

crictl pods

crictl pods --name <name>

# ctr events

Port Forward

crictl port-forward command allows you to forward local ports to containers running in a Kubernetes CRI (Container Runtime Interface) environment. Here's a comprehensive guide:

# crictl port-forward <container-id> [local-port]:<container-port>

Forward local port 8080 to container port 80

# crictl port-forward <container-id> 8080:80 & $ (&) for background

# Let crictl choose an available local port

crictl port-forward <container-id> :80 

Forward Multiple Ports

Forward multiple ports simultaneously

# crictl port-forward <container-id> 8080:80 8443:443

Pull directly from a registry 

# crictl pull docker.io/nginx:latest

Import a tarball with a specific image name and tag

# crictl import ubuntu-container.tar ubuntu-custom:latest

curl to download and import directly

# curl http://example.com/image.tar | crictl import - custom-image:v1.0

If using containerd directly

# ctr image import image.tar

Import with specific namespace

# ctr -n k8s.io image import image.tar