Build, Run & Push

Estimated time: 15–20 minutes

You will build the Dockerfile from the last page into a real image, run it, and publish it to Docker Hub so it can be pulled from anywhere.

Building the Image

Run the build

From the folder containing your Dockerfile, run:

Terminal


docker build -t my-next-app .

docker build — build an image from a Dockerfile
-t my-next-app — tag (name) the image my-next-app
. — the folder you are standing in right now (your project folder). This tells Docker where to find your project’s files for this build.

The first build takes longer, since Docker has to download the node:20-alpine base image and install every package. Run the same command again with no code changes — it finishes almost instantly, because every layer is cached.

Confirm it exists

Terminal


docker images

You should see my-next-app in the list, alongside nginx if you still have it from Foundation.

Running Your Image

A built image is not running yet — it is just sitting on your machine, waiting. docker run creates a container from it and starts it, the same command pattern you already know:

Terminal


docker run -d -p 3000:3000 --name my-next-app-container my-next-app

Open http://localhost:3000 . Your Next.js app is running — fully packaged, with no Node.js installation required on your machine to serve it.

If port 3000 is already in use (for example, by npm run dev running outside Docker), stop that first, or map to a different host port: -p 3001:3000, then visit localhost:3001 instead.

Understanding Tags

An image name has an optional tag, written as name:tag. If you do not specify one, Docker uses latest.

Terminal


docker build -t my-next-app:1.0 .
docker build -t my-next-app:latest .

Both commands can point at the exact same image — tags are just labels you choose. Using version tags (1.0, 1.1) instead of always relying on latest makes it clear which exact version is running, which matters once you deploy to a server.

Pushing to Docker Hub

Pushing makes your image pullable from any machine — a teammate’s laptop, or a production server — exactly like nginx is pullable by anyone.

Create a Docker Hub account

If you do not have one, sign up at https://hub.docker.com . It is free for public images.

Log in from your terminal

Terminal


docker login

Enter your Docker Hub username and password (or an access token, which Docker Hub lets you generate under Account Settings).

Tag the image with your username

A Docker Hub image name must start with your username, followed by a slash. Replace your-username below:

Terminal


docker tag my-next-app your-username/my-next-app:1.0

This does not create a new image — it adds a second name to the same image, one that Docker Hub will recognize as yours.

Push it

Terminal


docker push your-username/my-next-app:1.0

Verify

Go to https://hub.docker.com , open your profile, and confirm my-next-app is listed. Anyone can now run it with:

Terminal


docker run -p 3000:3000 your-username/my-next-app:1.0

Hands-on Task

Build your Next.js app into an image tagged my-next-app:1.0.
Run it and confirm it loads at localhost:3000.
Push it to Docker Hub under your own username.
Ask a friend (or use a different machine) to run docker run -p 3000:3000 your-username/my-next-app:1.0 and confirm it works for them too.

Quick Check

Can you explain what the . at the end of docker build -t my-next-app . means?
Do you know why the second build was faster than the first?
Can you explain why an image must be tagged with your username before pushing?

Next → Smaller Images