Copy Directory to Another Directory Using ADD Command

TLDR

The ADD command in Docker allows you to copy directories from your local filesystem or a URL into a Docker image. This is useful for including application files, configurations, or other resources during the build process.

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The ADD command in Docker is a versatile instruction that can copy files and directories into a Docker image. This guide explains how to use it effectively to copy directories.

Step 1: Understand the ADD Command

The ADD command has the following syntax:

ADD <source> <destination>

• <source>: The path to the directory or file to copy.
• <destination>: The path inside the image where the content will be copied.

Step 2: Copy a Local Directory

To copy a local directory into a Docker image, specify the source and destination paths.

Example

FROM ubuntu:latest

# Copy the local 'app' directory to '/usr/src/app' in the image
ADD app /usr/src/app

WORKDIR /usr/src/app
CMD ["bash"]

Explanation

• ADD app /usr/src/app: Copies the app directory from the build context to /usr/src/app in the image.
• WORKDIR /usr/src/app: Sets the working directory to /usr/src/app.

Step 3: Copy a Directory from a URL

The ADD command can also download and extract files from a URL.

Example

FROM ubuntu:latest

# Download and extract a tarball from a URL
ADD https://example.com/files/app.tar.gz /usr/src/app

WORKDIR /usr/src/app
CMD ["bash"]

Explanation

• ADD https://example.com/files/app.tar.gz /usr/src/app: Downloads and extracts the tarball to /usr/src/app.

Step 4: Preserve Directory Structure

The ADD command preserves the directory structure of the source.

Example

FROM ubuntu:latest

# Copy the entire 'config' directory
ADD config /etc/config

CMD ["bash"]

Explanation

• ADD config /etc/config: Copies the config directory and its contents to /etc/config.

Step 5: Use .dockerignore for Exclusions

To exclude certain files or directories, use a .dockerignore file.

Example .dockerignore

node_modules
*.log

Explanation

• Excludes node_modules and all .log files from being copied.

Best Practices

• Prefer COPY for Simplicity: Use COPY instead of ADD unless you need its advanced features (e.g., downloading from URLs).
• Use .dockerignore: Exclude unnecessary files to reduce image size.
• Validate Paths: Ensure source paths are correct and within the build context.

By following these steps, you can effectively use the ADD command to copy directories into Docker images, enabling efficient and organized builds.