Docker Mastery

Build Apps That Deploy Anywhere

Workbook: Building Images for Python, Go, and Ruby Applications

Key Takeaways

  • Universal Dockerfile Pattern: All programming languages follow the same four-step Dockerfile structure: base image → working directory → copy source code → execution command, regardless of language complexity
  • Language-Specific Base Images: Each language requires its appropriate base image foundation (ruby:3.0, python:3.8-slim, golang:1.16) to provide the necessary runtime environment
  • Base Image as Foundation Metaphor: The base image serves as the building foundation onto which all additional layers (working directory, source code, commands) are systematically added
  • Container Process Creation: When containers run applications, they start up language-specific processes within the container environment that execute the packaged source code
  • Automatic Working Directory Navigation: Containers intelligently navigate to the specified WORKDIR automatically, eliminating the need to specify full paths during execution
  • Environment Variables vs Command Line Arguments:
    • Environment variables: Set with -e flag, expected key-value pairs from the runtime environment
    • Command line arguments: Direct values passed to the application during execution
  • Interactive Shell Debugging: Use -it /bin/shell to create interactive sessions inside containers for debugging and understanding internal container structure
  • Dockerfile Context Consistency: The build context (current directory with .) must contain the Dockerfile and all source files referenced in COPY instructions
  • Simplified Container Management: Building custom images transforms complex docker run commands into simple, reusable image-based container creation