Containerize an application
For the rest of this guide, you'll be working with a simple todo list 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.
Prerequisites
- You have installed the latest version of Docker Desktop.
- You have installed a Git client.
- You have an IDE or a text editor to edit files. Docker recommends using Visual Studio Code.
Get the app
Before you can run the application, you need to get the application source code onto your machine.
Clone the getting-started-app repository using the following command:
$ git clone https://github.com/docker/getting-started-app.git
View the contents of the cloned repository. You should see the following files and sub-directories.
├── getting-started-app/ │ ├── .dockerignore │ ├── package.json │ ├── README.md │ ├── spec/ │ ├── src/ │ └── yarn.lock
Build the app's image
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.
In the
getting-started-app
directory, the same location as thepackage.json
file, create a file namedDockerfile
. 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 yourgetting-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 yourgetting-started-app
directory.$ cd \path\to\getting-started-app
Create an empty file named
Dockerfile
.$ type nul > Dockerfile
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 yourgetting-started-app
directory.$ cd \path\to\getting-started-app
Create an empty file named
Dockerfile
.$ New-Item -Path . -Name Dockerfile -ItemType File
Using a text editor or code editor, add the following contents to the Dockerfile:
# syntax=docker/dockerfile:1 FROM node:18-alpine WORKDIR /app COPY . . RUN yarn install --production CMD ["node", "src/index.js"] EXPOSE 3000
Build the image using the following commands:
In the terminal, make sure you're in the
getting-started-app
directory. Replace/path/to/getting-started-app
with the path to yourgetting-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 thenode: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. TheCMD
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 imagegetting-started
, you can refer to that image when you run a container.The
.
at the end of thedocker build
command tells Docker that it should look for theDockerfile
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.
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 terminal prompt. You can verify that a container is running by viewing it in Docker Dashboard under Containers, or by runningdocker ps
in the terminal.The
-p
flag (short for--publish
) creates a port mapping between the host and the container. The-p
flag takes a string value in the format ofHOST:CONTAINER
, whereHOST
is the address on the host, andCONTAINER
is the 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.After a few seconds, open your web browser to https://127.0.0.1:3000. You should see your app.
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.
Run the following docker ps
command in a terminal to list your containers.
$ docker ps
Output similar to the following should appear.
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
df784548666d getting-started "docker-entrypoint.s…" 2 minutes ago Up 2 minutes 127.0.0.1:3000->3000/tcp priceless_mcclintock
In Docker Desktop, select the Containers tab to see a list of your containers.
Summary
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:
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.