In the physical world, shipping containers revolutionized global trade because you could put anything inside them—furniture, electronics, cars—and they would fit perfectly on any ship, truck, or crane. Docker does the same for software. It packages your code, libraries, and settings into a single "unit" that runs exactly the same on any computer.
The Core Concepts
To understand Docker, you must distinguish between these three terms:
1. The Dockerfile
The Recipe. A text file containing the instructions to build your environment.
2. The Image
The Snapshot. A read-only template created from the Dockerfile. It’s like a frozen version of your computer.
3. The Container
The Instance. A living, breathing version of the Image. This is where your code actually runs.
Phase 1: Installation
Docker is most commonly used via Docker Desktop, which provides a graphical interface and the background engine needed to run containers.
Windows
Ensure WSL2 is enabled. Download the installer from the official site and follow the "Use WSL2 based engine" recommendation.
macOS
Choose the correct version for your chip (Intel vs Apple Silicon/M-series). Installation is a simple drag-and-drop to Applications.
Phase 2: Mastering the CLI
Once Docker is installed, your terminal becomes a cockpit. Here are the commands used by 2026's top engineers.
| Command | What it does | Mental Shortcut |
|---|---|---|
docker pull [image] |
Downloads an image from Docker Hub (like python or nginx). |
"Download the template." |
docker build -t [name] . |
Turns your Dockerfile into a usable Image. |
"Cook the recipe." |
docker run -d [image] |
Starts a container in the background (Detached mode). | "Launch the app." |
docker ps |
Lists all currently running containers. | "Who is awake?" |
docker stop [ID] |
Gracefully shuts down a container. | "Go to sleep." |
Deep Dive: Interactive & Cleanup Commands
To truly manage your system, you need these "Power User" commands:
Enter the Container Shell
If you need to "step inside" a running container to run commands manually:
docker exec -it [container_name] bash
The -it flag stands for Interactive Terminal.
The "Nuclear" Cleanup
Docker can eat up disk space quickly with old images and stopped containers. Run this to reclaim your storage:
docker system prune -a --volumes
Warning: This deletes everything not currently in use. Use with caution!
Phase 3: Networking (Port Mapping)
A container is isolated. If it's running a web server on port 80, your computer can't see it unless you "open a window" between the host and the container.
docker run -p 8080:80 nginx
This maps Local Port 8080 to Container Port 80. You can now visit localhost:8080 in your browser to see the server.
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