Understanding CRI-O: The What, Why, and How of its Definition in Container Platforms

46525256 - Understanding CRI-O: The What, Why, and How of its Definition in Container Platforms

Dive into the world of container technology with our comprehensive guide on CRI-O. Learn its functions, benefits, and how it’s shaping the future of Kubernetes deployment.


Join 2000+ tech leaders

A digest from our CEO on technology, talent and hard truth. Get it straight to your inbox every two weeks.

    No SPAM. Unsubscribe anytime.

    CRI-O is an innovation in the world of IT and containerization. This open-source software enables developers to run and manage containers using the Kubernetes cluster’s native interface. With an increasing global demand for containerization and automation, CRI-O is fast gaining popularity; it is now being used by thousands of IT professionals and organizations worldwide. In this comprehensive glossary, we delve into the nitty-gritty details of CRI-O, its functionality, and its advantages. We will also look at its real-life use cases, best practices, and recommended books on the subject.

    “CRI-O, an essential piece of the container ecosystem puzzle, bringing flexibility, standardization, and reliability to cloud-native environments.” – Kelsey Hightower

    What is CRI-O? Definition of Container Runtime Interface using OCI

    CRI-O is an acronym for Container Runtime Interface – Open Container Initiative. The project falls under the umbrella of the Kubernetes open-source community and adheres to the OCI runtime specifications. CRI-O, being a lightweight alternative to Docker, is tailored to run Kubernetes-native workloads. It covers the necessary components to execute, store, and manage Kubernetes’ container images, conforming to the CRI framework laid down by the Kubernetes project.

    ℹ️ Synonyms: Container Runtime Interface-O, CRI-O runtime, Open Container Initiative-compatible runtime

    How it Works

    >CRI-O operates through a Kubernetes CRI implementation that understands OCI-compatible container runtimes. Its components include:

    Runtime Server

    This is the core of the CRI-O system. It communicates with the Kubernetes kubelet, handles requests, and orchestrates container operations such as creating, starting, and stopping containers.

    Storage Library

    This library caters to storage requirements, like image layers and snapshot handling, by leveraging the functionality of the image and container layers provided by the OCI Image Format Spec and the OCI Runtime Spec respectively.

    Image Service

    Image Service communicates with container image registries and manages local image storage. The service can pull container images from remote registries, perform image verification, and manage and store image data.

    ā­  The Definition Demystified: What Exactly is SOA in Today's Tech World?

    Network Plugins

    CRI-O supports Container Network Interface (CNI) plugins to facilitate container networking within Kubernetes environments. These plugins take care of network setup, teardown, and configuration for the containers.

    Benefits of using CRI-O

    • Optimized for Kubernetes: CRI-O is built specifically for Kubernetes workloads, streamlining the process of deploying and managing containers in a Kubernetes cluster.
    • OCI Compatible: As an OCI-compliant runtime, CRI-O seamlessly works with various OCI-specified container formats and images, with no need for additional Kubernetes adaptation.
    • Lightweight: Its lean architecture eliminates unnecessary dependencies and bloat, increasing the overall efficiency of the container runtime environment.
    • Flexible and Extensible: CRI-O’s modular design supports a variety of container storage, runtime, and networking plugins to cater to diverse use cases and changing requirements.
    • Open-source Heritage: Being a part of the Kubernetes open-source community, CRI-O benefits from regular updates, bug fixes, and feature enhancements contributed by its user base.

    CRI-O use cases

    CRI-O’s practical applications span industries that require containerization and collaboration in software development. Among the key use cases are:

    Deployment of Kubernetes-native Applications

    Organizations and developers leveraging Kubernetes for their application workloads can deploy CRI-O for efficient container runtime management.

    Hybrid Cloud Environments

    CRI-O can be used to facilitate the management of containerized workloads in a hybrid cloud environment, simplifying the process of dealing with multiple cloud infrastructures.

    Edge Compute Deployments

    Due to its lightweight and optimized design, CRI-O is suitable for edge computing environments that demand high-performance container runtimes with minimal resource overhead.

    Code Examples

    # Download the CRI-O package archive
    wget https://storage.googleapis.com/cri-o/crio-1.18.tar.gz
    tar -xvzf crio-1.18.tar.gz
    # Install necessary dependencies
    sudo apt-get install -y libglib2.0-dev libseccomp-dev libapparmor-dev libgpgme11-dev
    # Build and install CRI-O from source
    cd crio
    sudo make install
    # Configure CRI-O
    sudo mkdir /etc/crio
    sudo cp etc/90-crio-bridge.conf /etc/sysctl.d/90-crio-bridge.conf
    sudo sysctl --system
    # Install the CRI-O CRIBS plugin
    sudo mkdir /usr/local/libexec/crio
    git clone https://github.com/cri-o/CRI-O.git
    cd cri-o
    make cribs
    sudo cp bin/cribs /usr/local/libexec/crio
    # Create the CRI-O configuration file
    cat <<EOF | sudo tee /etc/crio/crio.conf
    root = "/var/lib/containers/storage"
    runroot = "/var/run/containers/storage"
    content_trust = "tcp,localhost:6789"
    storage_driver = "overlay"
    log_level = "info"
    default_transport = "docker://"
    pause_image = "k8s.gcr.io/pause:3.1"
    pause_command = "/pause"
    signature_policy = ""
    image_volumes = "mkdir"
    runtime = "/usr/local/libexec/crio/cribs"
    conmon = "/usr/bin/conmon"
    seccomp_profile = "/etc/crio/seccomp.json"
    logfile = "/var/log/crio.log.pk"
    # Start the CRI-O service
    sudo systemctl enable crio
    sudo systemctl start crio

    Best Practices

    In order to make the most of CRI-O as your choice of container runtime, it is crucial to follow some best practices. These include staying updated with the latest CRI-O releases, ensuring you use compatible container images, and observing the Kubernetes’ best practices for containerization. This includes setting accurate resource limits, using liveness and readiness probes, and following security best practices for container networking.

    ā­  Exploring the Digital World: What is the True Definition of Bytecode?

    Most recommended books about CRI-O

    • “Kubernetes: Up and Running” by Kelsey Hightower, Brendan Burns, and Joe Beda
    • “Mastering Kubernetes” by Gigi Sayfan
    • “Kubernetes in Action” by Marko Luksa
    • “Kubernetes: A Step-by-Step Guide to Learn and Master Kubernetes” by Brayden Smith”
    • “Kubernetes Operators: Automating the Container Orchestration Platform” by Jason Dobies and Joshua Wood


    As organizations and developers continue to adopt containerization in their software development lifecycle, it’s crucial to have efficient container runtime management solutions. CRI-O is designed specifically for Kubernetes workloads, providing a lightweight and optimized alternative to other container runtimes. By understanding the benefits and best practices associated with CRI-O, professionals can enhance the performance and agility of their container management in Kubernetes environments.

    Tags: container, cri-o, definition, docker, kubernetes.

    Lou photo
    Back in 2013, I founded Echo with the simple business idea: "Connect great tech companies around the globe with the brightest software engineers in Eastern Europe." We've employed hundreds of talents so far and keep going.
    Lou photo
    li profile Lou Reverchuk

    IT Entrepreneur

    Notify of

    Inline Feedbacks
    View all comments
    Ready to discuss your hiring needs?