Understanding Kubernetes: Part 37 Container Runtime Interface (CRI)

📢 If you’ve been following our Kubernetes series 2025, welcome back! For new readers, check out Part 36 Container Network Interface (CNI)

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Container Runtime Interface (CRI) in Kubernetes

The Container Runtime Interface (CRI) is a plugin interface in Kubernetes that allows the kubelet to use different container runtimes for managing pods and containers. Kubernetes does not run containers directly; instead, it communicates with a container runtime via CRI to perform operations like pulling images, starting/stopping containers, and managing container networking.

Unlike Docker, which was directly integrated into Kubernetes in earlier versions, Kubernetes now interacts with container runtimes like containerd and CRI-O through the CRI.

Why is CRI Important?

1. Pluggability — Kubernetes can work with different container runtimes without modifying the kubelet.
2. Standardization — The CRI defines a standard API that all runtimes must implement, ensuring compatibility.
3. Performance — CRI-optimized runtimes (e.g., containerd, CRI-O) are lightweight and…