pouch_with_cri_introduction.md

PouchContainer with CRI introduction

What is CRI

The Container Runtime Interface (CRI) is a plugin interface which enables kubelet to use a wide variety of container runtimes, without the need to recompile. CRI (Container Runtime Interface) consists of a protobuf API,specifications/requirements and librariesfor container runtimes to integrate with kubelet on a node.

This diagram explains how the Container Runtime Interface works:

Why need to implement CRI in PouchContainer

The purpose of the PouchContainer CRI implementation is to integrate with Kubelet.This allows Kubernetes to directly launch and manage containers through the PouchContainer CRI.

Application scene

Manage containers via Kubernetes.

PouchContainer CRI Create a single-container pod

Let's use an example to demonstrate how pouch-cri works for the case when Kubelet creates a single-container pod:

• Kubelet calls pouch-cri, via the CRI runtime service API, to create a pod.
• PouchContainer uses containerd to create and start a special pause container (the sandbox container) and put that container inside the pod's cgroups and namespace (steps omitted for brevity).
• PouchContainer configures the pod's network namespace using CNI.
• Kubelet subsequently calls pouch-cri, via the CRI image service API, to pull the application container image.
• Kubelet then calls pouch-cri, via the CRI runtime service API, to create and start the application container inside the pod using the pulled container image.
• PouchContainer finally calls containerd to create the application container, put it inside the pod's cgroups and namespace, then to start the pod's new application container.

After these steps, a pod and its corresponding application container is created and running.

PouchContainer CRI workflow

This diagram briefly explains PouchContainer CRI internal module workflow：