Docker Basics

What is Docker?

Docker is a tool that packages your app and everything it needs to run into a neat, self-contained box called a container.

Here's why that matters. Your app doesn't run in a vacuum. It needs specific versions of programming languages, libraries, databases, and other tools. On your computer, those things might be set up one way. On someone else's computer, they're set up differently. This is where the classic developer headache comes from: "it works on my machine."

Docker solves this. A container includes your app and everything it needs — the right version of Python or Node.js, the right libraries, the right database. It runs the same way everywhere. Your laptop, your friend's laptop, a server on the internet. Identical.

The moving truck analogy

Think of it like moving apartments. You could carry your furniture piece by piece, set it up in the new place, and hope you remembered how everything was arranged. Or you could pack your entire apartment into a shipping container — furniture, decorations, everything exactly where it belongs — and drop the whole container into the new place. That's Docker. Your app is the apartment. The container is the shipping container. Everything inside stays exactly the same no matter where the container goes.

Why do vibe coders need Docker?

You might be thinking: "I'm just building a simple app. Do I really need this?"

For your very first project, maybe not. But the moment your app needs a database, or uses a specific version of Node.js, or has more than a few dependencies — Docker saves you from a world of pain. Here's what it prevents:

"It was working yesterday." Without Docker, updating something on your computer (even something unrelated) can break your app. With Docker, your app runs inside its container, isolated from everything else.

"I can't install the right version." Different projects sometimes need different versions of the same tool. Docker lets each project have exactly what it needs without conflicts.

"How do I set this up on a server?" When you're ready to put your app on the internet, Docker makes deployment dramatically simpler. The same container that runs on your laptop runs on the server.

Install Docker

Mac

You should see something like Docker version 27.x.x. The exact number doesn't matter — as long as it shows a version, you're good.

Windows

Restart your computer when prompted. This sets up a lightweight Linux layer that Docker uses behind the scenes.

Linux

Open your terminal and run:

Log out and log back in for the group change to take effect. Then verify:

The commands you'll actually use

Docker has a lot of commands. You need about five of them. Here they are.

docker compose up

This is the big one. It reads a file called docker-compose.yml (which AI will typically generate for your project) and starts all the services your app needs — the app itself, a database, whatever's defined in that file.

Add -d to run it in the background (so your terminal isn't tied up):

docker compose down

Stops everything that docker compose up started.

docker ps

Shows you what's currently running. Useful when you want to check if your containers are actually up.

docker compose logs

Shows the output from your containers. If something's not working, this is where you look for error messages.

Add -f to follow the logs in real time (like a live feed). Press Ctrl+C to stop watching.

docker compose build

Rebuilds your containers. Use this when you've changed your Dockerfile or docker-compose.yml and need the changes to take effect.

Common gotchas

"Docker daemon is not running." Docker Desktop needs to be open. Check your menu bar (Mac) or system tray (Windows) for the whale icon. If it's not there, launch Docker Desktop.

"Permission denied." On Linux, make sure you added your user to the docker group (the sudo usermod command from the install step). On Mac/Windows, this usually means Docker Desktop isn't running.

"Port already in use." Another app (or another container) is using the same port. Either stop the other thing or change the port in your docker-compose.yml. AI can help you with this — just tell it which port is conflicting.

It's slow the first time. The first time you run docker compose up, Docker downloads all the base images your app needs. This can take a few minutes depending on your internet speed. After the first time, it's cached and much faster.

"No space left on device." Docker images accumulate over time. Clean up old stuff with:

It will ask for confirmation. Type y and hit Enter. This removes stopped containers, unused networks, and dangling images.