This rule emphasizes the importance of pinning versions when using pip to install Python packages in your Dockerfile. Pinning versions means specifying the exact version of the package you want to install. Without pinning, pip installs the latest version of the package, which may not be compatible with your application.
Pinning versions is crucial for maintaining the stability and reproducibility of your Docker images. Without pinning, your builds could suddenly start failing because of a new package version that introduces breaking changes. Your application could also behave differently or even fail when running in different environments, due to variations in package versions.
To avoid these issues, always specify the exact version of the package when using pip install. For example, instead of RUN pip install django, use RUN pip install django==1.9. If you have a list of packages to install, you can put them in a requirements.txt file with their versions pinned, and then install them with RUN pip install -r requirements.txt. This practice will ensure that you always know exactly what versions of packages are in your Docker images, and your builds will be stable and reproducible.