Painless Docker - 2nd Edition

Optimizing Docker Builds: Reducing the Context Size

When building Docker images, the build context plays a crucial role in determining the efficiency and speed of the build process. The build context is the set of files and directories that are sent to the Docker daemon during the build. A large build context can lead to slower builds, increased resource consumption, and potential security risks if sensitive files are included.

In our previous example, the context was the entire directory containing the Dockerfile and application code. However, if this directory contains unnecessary files (like documentation, tests, or local configuration files), they will be sent to the Docker daemon.

A common case is when the project directory contains your source code along with your git metadata (the .git folder). This folder isn't needed for your container build and can add additional overhead. Other files that are commonly excluded include:

• Compiled files (e.g., .pyc, .o, etc.)
• Temporary files (e.g., editor backups, OS-specific files like .DS_Store, etc.)
• Dependency directories (e.g., node_modules, vendor, etc.)
• IDE configuration files (e.g., .vscode, .idea, etc.)
• Environment files (e.g., .env