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Docker is a containerization platform, while Kubernetes (K8s) is a container orchestration platform. They are not competitors; historically, they worked together perfectly.
For many years, Docker was the default container runtime for Kubernetes. When you deployed a pod to Kubernetes, K8s would use the Docker Engine running on the node to start the containers.
However, Docker was not designed specifically for Kubernetes. It included many extra features (like Docker Swarm, volumes, and networks) that Kubernetes didn't need and preferred to manage itself.
Kubernetes introduced the CRI, an API that allows K8s to use any compatible container runtime without recompiling the cluster components.
Because the Docker Engine did not support the CRI natively, Kubernetes maintained a translation layer called dockershim. In Kubernetes version 1.24, dockershim was officially removed.
Almost nothing changes for your daily workflow.
You still use Docker Desktop or the Docker CLI to build your Docker images (which are actually OCI-compliant images). You still push them to a registry like Docker Hub or AWS ECR.
When Kubernetes pulls your image, it simply uses a more lightweight, CRI-compliant runtime (like containerd or CRI-O) to run the image instead of the full Docker Engine. Since containerd was actually spun out of Docker itself, your images will run exactly as expected.
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