Containerize an application (2024)

For the rest of this guide, you'll be working with a simple todolist manager that runs on Node.js. If you're not familiar with Node.js,don't worry. This guide doesn't require any prior experience with JavaScript.

• You have installed the latest version ofDocker Desktop.
• You have installed aGit client.
• You have an IDE or a text editor to edit files. Docker recommends usingVisual Studio Code.

Get the app

Before you can run the application, you need to get the application source code onto your machine.

1. Clone thegetting-started-app repository using the following command:

   $ git clone https://github.com/docker/getting-started-app.git

2. View the contents of the cloned repository. You should see the following files and sub-directories.

   ├── getting-started-app/│ ├── package.json│ ├── README.md│ ├── spec/│ ├── src/│ └── yarn.lock

To build the image, you'll need to use a Dockerfile. A Dockerfile is simply a text-based file with no file extension that contains a script of instructions. Docker uses this script to build a container image.

1. In the getting-started-app directory, the same location as the package.json file, create a file named Dockerfile. You can use the following commands to create a Dockerfile based on your operating system.

   In the terminal, run the following commands.

   Make sure you're in the getting-started-app directory. Replace /path/to/getting-started-app with the path to your getting-started-app directory.

   $ cd /path/to/getting-started-app

   Create an empty file named Dockerfile.

   $ touch Dockerfile

   In the Windows Command Prompt, run the following commands.

   Make sure you're in the getting-started-app directory. Replace \path\to\getting-started-app with the path to your getting-started-app directory.

   $ cd \path\to\getting-started-app

   Create an empty file named Dockerfile.

   $ type nul > Dockerfile

   See Also

   A Docker Tutorial for BeginnersHow to Check for Docker InstallationHow To Install and Use Docker on Ubuntu 18.04 | DigitalOceanInstall Docker Desktop on Windows

   In PowerShell, run the following commands.

   Make sure you're in the getting-started-app directory. Replace \path\to\getting-started-app with the path to your getting-started-app directory.

   $ cd \path\to\getting-started-app

   Create an empty file named Dockerfile.

   $ New-Item -Path . -Name Dockerfile -ItemType File

2. Using a text editor or code editor, add the following contents to the Dockerfile:

   # syntax=docker/dockerfile:1FROM node:18-alpineWORKDIR /appCOPY . .RUN yarn install --productionCMD ["node", "src/index.js"]EXPOSE 3000

3. Build the image using the following commands:

   See Also

   Install Docker Engine on Ubuntu

   In the terminal, make sure you're in the getting-started-app directory. Replace /path/to/getting-started-app with the path to your getting-started-app directory.

   $ cd /path/to/getting-started-app

   Build the image.

   $ docker build -t getting-started .

   The docker build command uses the Dockerfile to build a new image. You might have noticed that Docker downloaded a lot of "layers". This is because you instructed the builder that you wanted to start from the node:18-alpine image. But, since you didn't have that on your machine, Docker needed to download the image.

   After Docker downloaded the image, the instructions from the Dockerfile copied in your application and used yarn to install your application's dependencies. The CMD directive specifies the default command to run when starting a container from this image.

   Finally, the -t flag tags your image. Think of this as a human-readable name for the final image. Since you named the image getting-started, you can refer to that image when you run a container.

   The . at the end of the docker build command tells Docker that it should look for the Dockerfile in the current directory.

Start an app container

Now that you have an image, you can run the application in a container using the docker run command.

1. Run your container using the docker run command and specify the name of the image you just created:

   $ docker run -dp 127.0.0.1:3000:3000 getting-started

   The -d flag (short for --detach) runs the container in the background.This means that Docker starts your container and returns you to the terminalprompt. You can verify that a container is running by viewing it in DockerDashboard under Containers, or by running docker ps in the terminal.

   The -p flag (short for --publish) creates a port mapping between the hostand the container. The -p flag takes a string value in the format ofHOST:CONTAINER, where HOST is the address on the host, and CONTAINER isthe port on the container. The command publishes the container's port 3000 to127.0.0.1:3000 (localhost:3000) on the host. Without the port mapping,you wouldn't be able to access the application from the host.

2. After a few seconds, open your web browser tohttp://localhost:3000.You should see your app.

   

3. Add an item or two and see that it works as you expect. You can mark items as complete and remove them. Your frontend is successfully storing items in the backend.

At this point, you have a running todo list manager with a few items.

If you take a quick look at your containers, you should see at least one container running that's using the getting-started image and on port 3000. To see your containers, you can use the CLI or Docker Desktop's graphical interface.

$ docker ps

CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMESdf784548666d getting-started "docker-entrypoint.s…" 2 minutes ago Up 2 minutes 127.0.0.1:3000->3000/tcp priceless_mcclintock

In this section, you learned the basics about creating a Dockerfile to build an image. Once you built an image, you started a container and saw the running app.

Related information:

• Dockerfile reference
• docker CLI reference
• Build with Docker guide

Next steps

Next, you're going to make a modification to your app and learn how to update your running application with a new image. Along the way, you'll learn a few other useful commands.