Optimize Dockerfile layer caching to improve build performance

[ronit-1404]

Short Description

Restructure Dockerfile COPY commands to improve layer caching efficiency and reduce Docker build times.

Possible Labels

• enhancement
• docker

Select Category

• Enhancement
• Add License/Copyright
• Scan Feature
• Packaging
• Documentation
• Expand Support
• Other

Describe the Update

The current Dockerfile uses COPY . /scancode-toolkit which copies the entire source directory before running the configuration step. This approach invalidates all subsequent Docker layers whenever any file changes (including documentation, samples, or tests), forcing unnecessary rebuilds of the expensive ./configure and license indexing steps.

This update restructures the COPY commands to:

1. Copy only essential configuration and source files first
2. Run the configuration and license indexing steps
3. Copy remaining runtime files afterwards

How This Feature will help you/your organization

Benefits:

• Faster Docker builds: Changes to non-essential files (docs, samples, README) won't invalidate the configure layer
• Improved CI/CD performance: Significantly reduced build times in continuous integration pipelines
• Better developer experience: Local Docker builds complete faster during development
• Cost savings: Reduced compute time in cloud-based CI/CD systems

Impact: The ./configure and scancode-reindex-licenses steps are time-consuming. With proper layer caching, these only rebuild when actual source code or configuration files change, not when documentation is updated.

Possible Solution/Implementation Details

Replace the single COPY . /scancode-toolkit command with selective, ordered COPY commands:

# Copy configuration files first
COPY configure configure.bat setup.py setup.cfg setup-mini.cfg pyproject.toml MANIFEST.in ./
COPY requirements*.txt ./
COPY src/ ./src/
COPY etc/ ./etc/

# Run configuration (this layer is now cached unless above files change)
RUN ./configure && ./venv/bin/scancode-reindex-licenses

# Copy runtime files
COPY scancode scancode.bat extractcode extractcode.bat ./
COPY *.rst *.LICENSE *.ABOUT NOTICE ./