EXPOSE instruction for ports in Docker - Mini Project: Build & Apply

Using the EXPOSE Instruction to Open Ports in Docker

📖 Scenario: You are creating a Docker image for a simple web application. To allow the application to communicate with the outside world, you need to open a specific port inside the container.

🎯 Goal: Learn how to use the EXPOSE instruction in a Dockerfile to open a port for your application.

📋 What You'll Learn

Create a Dockerfile with a base image

Add the EXPOSE instruction for a specific port

Build the Docker image

Run the container and verify the port is exposed

💡 Why This Matters

🌍 Real World

Opening ports in Docker containers is essential to allow applications inside containers to communicate with users or other services.

💼 Career

Understanding how to expose ports is a fundamental skill for DevOps engineers and developers working with containerized applications.

1

Create a Dockerfile with a base image

Create a file named Dockerfile and add a line to use the base image nginx:latest.

Docker

# Create a Dockerfile with the base image nginx:latest
# Your code here

Need a hint?

The first line in a Dockerfile usually starts with FROM followed by the image name.

2

Add the EXPOSE instruction for port 80

Add a line to the Dockerfile to expose port 80 using the EXPOSE instruction.

Docker

FROM nginx:latest
# Add EXPOSE instruction for port 80 below
# Your code here

Need a hint?

Use EXPOSE 80 to tell Docker to open port 80 inside the container.

3

Build the Docker image

Run the command docker build -t my-nginx . in your terminal to build the Docker image with the tag my-nginx.

Docker

FROM nginx:latest
EXPOSE 80
# Run docker build command in terminal
# Your code here

Need a hint?

Open your terminal and run docker build -t my-nginx . to create the image.

4

Run the container and verify the port is exposed

Run the container with docker run -d -p 8080:80 --name webserver my-nginx and then run docker ps to check that port 8080 on your machine maps to port 80 in the container.

Docker

FROM nginx:latest
EXPOSE 80
# Run docker run command and docker ps to verify
# Your code here

Need a hint?

Use docker run -d -p 8080:80 --name webserver my-nginx to start the container and docker ps to see the port mapping.