Build tools must allow us to ensure consistency and repeatability. If two people attempt to build the same product at the same revision number in the source code repository on different machines, we expect identical results.36 Our builds are hermetic, meaning that they are insensitive to the libraries and other software installed on the build machine. Instead, builds depend on known versions of build tools, such as compilers, and dependencies, such as libraries. The build process is self-contained and must not rely on services that are external to the build environment.

Rebuilding older releases when we need to fix a bug in software that’s running in production can be a challenge. We accomplish this task by rebuilding at the same revision as the original build and including specific changes that were submitted after that point in time. We call this tactic cherry picking. Our build tools are themselves versioned based on the revision in the source code repository for the project being built. Therefore, a project built last month won’t use this month’s version of the compiler if a cherry pick is required, because that version may contain incompatible or undesired features.

Source: Chapter 8 - Release Engineering