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Docker Filesystem Internals (Advanced) Docker Filesystem Internals (Advanced) This post is for readers who already understand Docker basics and want to learn how Docker manages files internally. If you are new to Docker, read the beginner guide first. Containers Do NOT Have Their Own Disk A common misunderstanding is that Docker containers have their own disk. In reality: Containers do not have a separate physical filesystem. Docker creates a filesystem view using layers stored on the host machine. This layered filesystem is implemented using a Union Filesystem , most commonly OverlayFS on Linux. Docker Images Are Read-Only Layers A Docker image is made up of multiple read-only layers. Each instruction in a Dockerfile creates a new layer. FROM python:3.11 RUN pip install flask COPY app.py . ...

🐳 Explained with a Simple Python Example (Beginner Friendly) Docker Explained Using a Very Simple App (Beginner Friendly) Goal: Build a tiny Python app, run it normally, then run the same app using Docker, and understand why Docker helps. Step 1: Create a Very Small Python App Create a file named app.py : print("Hello I am running inside Docker!") Step 2: Run the App WITHOUT Docker Run this on your machine: python app.py Common real-life problems: Python not installed, wrong Python version, missing dependencies, different OS behavior this is where the “works on my machine” issue starts. Step 3: Introduce Docker Instead of relying on your system, Docker lets you package the runtime (Python) together with your app. We’ll do that using a Dockerfile . Step 4: Create a Dockerfile Create a file named Dockerfile (no extension): ...