Where to Use COPY and ADD in Your Dockerfile

When creating Docker images, COPY and ADD help you manage files inside your container. Here's a quick guide on how to use them with a basic Apache web server example.

What Are COPY and ADD?

COPY: Moves files from your computer into the Docker image. Use this for straightforward file transfers.

ADD: Similar to COPY, but can also handle compressed files and download files from URLs.

When to Use COPY

Copy Files: Use COPY to move files like your website content into the Docker image.

# Use the official Apache image
FROM httpd:2.4

# Copy website files
COPY html/ /usr/local/apache2/htdocs/

# Expose port 80
EXPOSE 80

When to Use ADD

Extract Tarballs: Use ADD to extract compressed files (e.g., .tar.gz) directly into the Docker image.

# Use the official Apache image
FROM httpd:2.4

# Download a file from a URL
ADD https://example.com/file.txt /usr/local/apache2/htdocs/

# Expose port 80
EXPOSE 80

Best Practices

Use COPY for Simple Tasks: It’s easier and more straightforward.
Use ADD for Tarballs or Downloads: If you need to handle compressed files or download from a URL.

Conclusion

Use COPY for basic file transfers and ADD for more advanced needs like extracting tarballs or downloading files. This helps keep your Dockerfiles clear and efficient.