Software Engineering at Google

Chapter 18. Build Systems and Build Philosophy

Written by Erik Kuefler

Edited by Lisa Carey

If you ask Google engineers what they like most about working at Google (besides the free food and cool products), you might hear something surprising: engineers love the build system.¹ Google has spent a tremendous amount of engineering effort over its lifetime in creating its own build system from the ground up, with the goal of ensuring that our engineers are able to quickly and reliably build code. The effort has been so successful that Blaze, the main component of the build system, has been reimplemented several different times by ex-Googlers who have left the company.² In 2015, Google finally open sourced an implementation of Blaze named Bazel.

Purpose of a Build System

Fundamentally, all build systems have a straightforward purpose: they transform the source code written by engineers into executable binaries that can be read by machines. A good build system will generally try to optimize for two important properties:

Fast

A developer should be able to type a single command to run the build and get back the resulting binary, often in as little as a few seconds.

Correct

Every time any developer runs a build on any machine, they should get the same result (assuming that the source files and other inputs are the same).

Many older build systems attempt to make trade-offs between speed and correctness by taking shortcuts that can lead to inconsistent builds. Bazel’s main objective is ...