Building and Configuring Custom Docker Images: From Execution Mechanics to Global Distribution

If you know how to run Docker containers but still feel unclear about what actually controls container execution , startup behavior , image layering , and runtime customization , this is where everything starts making sense. A Docker image is not just a package of code. It is a complete execution blueprint. Once you understand how Docker interprets that blueprint, you stop copying Dockerfiles from the internet and start designing them intentionally. In this article, we’ll break down: Why containers stop immediately CMD vs ENTRYPOINT with real behavior How Docker layers work internally Why environment variables matter How to build reusable images How to publish them globally through Docker Hub Why Containers Exit Immediately A container runs only as long as its main process is alive . Unlike virtual machines, containers are not designed to stay alive by default. They exist only to execute a specific process. Example: docker run ubuntu docker ps -a You may notice: Exited ( 0 ) Why? Becau