Docker to Kubernetes: How Container Images Become Running Pods

2026-05-06 · Source: Data Science on Medium · Field: Technology & Digital — Software Development & Engineering, Cloud Computing & IT Infrastructure · Depth: Intermediate, short

Summary

This article details the four-step process by which a Docker image transitions into a running Kubernetes Pod. It begins with building a Docker image locally using a `Dockerfile` and tagging it, for example, `my-app:v1`. The second step involves pushing this image to a container registry such as Docker Hub, AWS ECR, or GCR, making it accessible to Kubernetes nodes. Crucially, the article emphasizes avoiding the `:latest` tag in deployments, advocating for explicit versioning like `v1.2.3`. The third step explains that Kubernetes pulls and runs the image not directly via the Docker daemon, but through a container runtime like containerd, which communicates via the CRI (Container Runtime Interface). Finally, the image runs within a Kubernetes Pod, the smallest deployable unit, which can encapsulate one or more containers, providing shared networking and storage, and a unified lifecycle.

Key takeaway

For DevOps Engineers deploying containerized applications to Kubernetes, understanding the internal flow from Docker image to running Pod is critical. You should always use explicit version tags for your container images to ensure deployment predictability and avoid issues with `:latest`. Familiarity with the role of containerd and the CRI, even if your workflow remains unchanged, provides a deeper insight into Kubernetes' operational efficiency and scalability.

Key insights

Docker images become Kubernetes Pods through a build, push, pull, and runtime orchestration sequence.

Principles

• Use explicit image version tags.
• Kubernetes uses CRI-compatible runtimes, not Docker daemon.

Method

Build a Docker image, push it to a registry, then Kubernetes pulls it via CRI to run within a Pod on a Node.

In practice

• Build images with `docker build -t my-app:v1 .`
• Push images to registry with `docker push username/my-app:v1`
• Deploy with `kubectl apply -f deployment.yaml`

Topics

• Docker
• Kubernetes
• Container Images
• Container Registry
• Container Runtime Interface

Best for: Software Engineer, DevOps Engineer

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Editorial summary, takeaway, and curation by AIssential. Original article published by Data Science on Medium.