Creating Docker Images with Dockerfile

A Dockerfile is a text file containing instructions for building a Docker image.
It automates the process of creating containers, making it reproducible and easy to manage.

Docker allows you to create custom images using a special file called a Dockerfile.
In this guide, we’ll go over the basics of working with a Dockerfile and create a simple image based on Ubuntu 22.04 with nginx.

Main Dockerfile Instructions

1. FROM — sets the base image (e.g., FROM ubuntu:22.04).
2. RUN — executes commands inside the container (e.g., RUN apt-get update).
3. COPY / ADD — copies files from the host machine into the container.
4. WORKDIR — sets the working directory.
5. EXPOSE — specifies which ports will be available.
6. CMD / ENTRYPOINT — defines the command that will run when the container starts.

Example Dockerfile

FROM python:3.9-slim  
WORKDIR /app  
COPY requirements.txt .  
RUN pip install -r requirements.txt  
COPY . .  
EXPOSE 8000  
CMD ["python", "app.py"]  

Building an Image

docker build -t my-app:latest .

Optimization Tips

• Use .dockerignore to exclude unnecessary files.
• Combine RUN commands to reduce image layers.
• Choose minimal base images (e.g., alpine).

1. Installing Docker

Before getting started, install Docker:

sudo apt update
sudo apt install -y docker.io

Verify installation:

docker --version

2. Creating a Dockerfile

Create a project directory and a Dockerfile:

mkdir mydocker
cd mydocker
nano Dockerfile

Add the following code to your Dockerfile:

# Load the base image Ubuntu 22.04
FROM ubuntu:22.04

# Update Ubuntu package repository
RUN apt-get update

# Install nginx
RUN apt-get install -y nginx && \
    rm -rf /var/lib/apt/lists/*

# Set environment variables
ENV nginx_conf /etc/nginx/nginx.conf

# Configure nginx
COPY default /etc/nginx/sites-available/default
RUN echo "\ndaemon off;" >> ${nginx_conf}

# Configure volumes
VOLUME ["/etc/nginx/sites-enabled", "/etc/nginx/certs", "/etc/nginx/conf.d", "/var/log/nginx", "/var/www/html"]

# Configure services and ports
CMD ["nginx", "-g", "daemon off;"]

# Expose nginx ports
EXPOSE 80 443

3. Building the Docker Image

Now build the image with the name mynginx:

docker build -t mynginx .

Check the list of images:

docker images

4. Running the Container

Once the image is created, run the container:

docker run -d -p 8080:80 -p 8443:443 mynginx

Test it:

curl http://localhost:8080

Or open in a browser: http://localhost:8080

5. Managing the Container

Stop a container:

docker stop <container_id>

Remove a container:

docker rm <container_id>

Remove the image:

docker rmi mynginx

Conclusion

We created an image based on Ubuntu 22.04, installed nginx, and set up its configuration.
Using a Dockerfile allows you to automate the build and deployment process.

A Dockerfile simplifies application deployment and ensures a consistent environment across systems.

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