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Run Your First Container (and Meet nginx)

In the last lesson you ran docker run hello-world and saw a friendly message. That was your first container - but it ran for a split second and then vanished. In this lesson we'll slow down, understand what actually happened, and then run a real web server you can open in your browser. 🌐

What we will do (in very simple steps)

  1. Understand what hello-world actually did
  2. Run a real web server called nginx
  3. Open it in your browser
  4. Check on it, then clean it up

Step 1: What did hello-world actually do?

When you ran that command, Docker quietly did four things:

  1. Looked for the hello-world image on your computer
  2. Downloaded it (because you didn't have it yet)
  3. Started a container from that image
  4. The container printed its message and immediately finished

Remember our kitchen analogy? The image is the packaged meal (a template, sitting on a shelf). A container is that meal actually being served. The hello-world meal is tiny - it says hello and it's done, like a single bite. 🍬

Most real containers aren't like that. They stay running and keep doing a job - which is exactly what we'll see next.

Step 2: Run a real web server

We're going to run nginx (say it "engine-x"), a popular web server. Unlike hello-world, it stays running and waits to serve web pages.

Run this:

docker run -d -p 8080:80 --name my-web nginx

That's a few new pieces, so here's each one in plain English:

  • docker run - start a new container
  • -d - "detached": run it in the background so you get your prompt back
  • -p 8080:80 - connect port 8080 on your computer to port 80 inside the container (think of it as running a hallway between your door and the container's door)
  • --name my-web - give the container a friendly name so it's easy to refer to later
  • nginx - the image to run

Docker will download nginx the first time (a few seconds), then print a long string of letters and numbers. That's the container's ID, and it means nginx is now running in the background. ✅

💡 Why port 8080 and not 80? Port 80 is often already in use or needs special permissions. 8080 is a safe, free choice for local practice.

Step 3: See it in your browser

Open your web browser and go to:

http://localhost:8080

You should see a page that says "Welcome to nginx!" 🎉

Take a second to appreciate this: a fully working web server is running on your machine, and you never installed nginx directly. It came fully packaged inside the container.

Step 4: Check on your container

Back in your terminal, run:

docker ps

ps lists your running containers. You'll see something like this (it's wide, so it may wrap on your screen):

CONTAINER ID   IMAGE   STATUS         PORTS                    NAMES
a1b2c3d4e5f6   nginx   Up 2 minutes   0.0.0.0:8080->80/tcp     my-web

That confirms your my-web container is Up (running) and shows the port hallway we built: 8080->80.

Step 5: Stop and clean up

Let's switch it off tidily. First stop it:

docker stop my-web

Then remove it completely:

docker rm my-web
  • stop turns the container off (like switching off the appliance)
  • rm removes it entirely (throws the switched-off container away)

Run docker ps again and the list will be empty - your container is gone. Don't worry, we'll go much deeper into stopping, starting, and removing in the Container Lifecycle lesson. This was just tidying up after ourselves.

✅ Checkpoint

You've finished this lesson if:

  • docker run -d -p 8080:80 --name my-web nginx started without errors
  • http://localhost:8080 showed the "Welcome to nginx!" page
  • docker ps listed my-web as Up
  • docker stop my-web and docker rm my-web left docker ps empty

🩹 Common hiccups

  • "port is already allocated": something is already using 8080. Either stop that program, or pick another port, e.g. -p 8081:80, and visit http://localhost:8081.
  • "The container name '/my-web' is already in use": you still have a container with that name from a previous try. Remove it with docker rm -f my-web, then run the command again.
  • Browser page won't load: check docker ps shows the container as Up. If it's missing, the container may have failed to start - re-run the docker run command and read any error message.

Next up: Understanding Images vs Containers - the single most useful mental model in all of Docker.