BazelCon 2024

At MongoDB we do not have one central codebase or only one language. As we continue to scale this fractured ecosystem is harder to maintain so we needed to migrate these disparate repos to a shared development platform. Our first step in that journey is migrating large repos to be built with Bazel so that the build team can make a feature once and it can benefit all of our developers. MongoDB’s approach to doing this is novel because we were able to de-risk these projects by supporting significant interoperability during migration. The downside, which is what most of this talk will be about, is dealing with the large amount of configuration in the build system. For example, the MongoDB C++ codebase had ~112 configuration options and remote compilation (not with RBE) before this process began and before converting even a single target we needed to support many of these configuration options and two remote execution environments. We are going to speak about the tools we used and created for these transitions, techniques we used for maintaining our hybrid build system, and how you too can switch to Bazel gradually and gently with the enthusiastic support of your organization.