Exposing multiple ports in a Docker container

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Exposing multiple ports in a Docker container

Author：JIYIK Last Updated：2025/03/24 Views：

There are different types of communication on the Internet, the most common ones include file transfers, sending emails, and serving web pages. To make this communication possible, we make use of port numbers that help identify the type of communication.

For example, File Transfer Protocol uses ports 20 and 21, Simple Mail Transfer Protocol uses 25, and Hypertext Transfer Protocol uses 25.

Similarly, Docker containers use ports to enable communication between different devices on the World Wide Web. In this article, we will learn how to expose multiple ports in a Docker container using the Nginx application.

Creating an NGINX Application

Open WebStorm IDEA and select File > New > Project. In the window that opens, select Empty Project and change the project name from untitled to web-app.

Finally, press the button labeled Create to create an empty project.

请注意, we can also use any other development environment as it does not matter what development environment you use. Since NGINX is used to serve static content, we do not need any additional configuration files.

After the project is built, create a file called index.js in the web-app folder and copy and paste the following code into the file.

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<h1>Welcome to Nginx !</h1>

</body>
</html>

This file contains a simple web page with a title that helps us test the application. Modify the HTML content to display whatever content you want.

Create a Dockerfile

Create a file called Dockerfile in the web-app folder and copy and paste the following instructions into the file.

FROM nginx:1.23.1-alpine
ADD . /usr/share/nginx/html

FROM - sets the base image on which to create the custom image, in our case we use alpine to extract a lightweight version of NGINX.
ADD - Copies the files and folders in the current folder to our mirrored file system /usr/share/nginx/html.

Building an Image

Use the keyboard shortcut ALT+F12 to open a new terminal window in your development environment and use the following command to create an image with the tag web-app:latest.

~/WebstormProjects/web-app$ docker build --tag web-app:latest .

This command executes our Dockerfile. We can view the two instructions executed in sequence as follows.

=> [1/2] FROM docker.io/library/nginx:1.23.1-alpine@sha256:082f8c10bd47b6acc8ef15ae61ae45dd8fde0e9f389a8b5cb23c3740  0.2s
 => => resolve docker.io/library/nginx:1.23.1-alpine@sha256:082f8c10bd47b6acc8ef15ae61ae45dd8fde0e9f389a8b5cb23c3740  0.2s
 => CACHED [2/2] ADD . /usr/share/nginx/html

Running a Docker container with multiple ports

In the same terminal window that you used to build the image, use the following command to run a container named web-app-prod listening on port 80 on the container, with ports 3000 and 5000 on the host.

~/WebstormProjects/web-app$ docker run --name web-app-prod -d -p 3000:80 -p 5000:80 web-app:latest

To expose multiple ports on the container, we used two consecutive -p flags to allocate two different ports on the host to listen on port 80 on the container.

Test Port

To verify that our containers are working as expected, open any browser and make requests to localhost:3000 ( http://localhost:3000/ ) and localhost:5000 ( http://localhost:5000/ ). Since the ports are listening to the same container, we get the same page of the NGINX application returned for both requests, as shown below.

Testing the Ports - Localhost 3000

Testing the Ports - Localhost 5000

Summarize

This article taught us how to expose multiple ports in a Docker container using the NGINX application. Note that this is the most common way to expose multiple ports, but we can use other methods to achieve the same goal.

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Next：Recreate the container from the new image using Docker-Compose

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