BazelCon 2024

rules_nixpkgs brings the power of Nix to Bazel dependencies. It provides access to the large nixpkgs package repository and benefits from hermeticity and declarative configurations that are dear to both the Bazel and Nix communities. But despite all the benefits, it still comes with one major downside. It makes remote execution of Bazel actions next to impossible but for some restricted use cases. In short, rules_nixpkgs and remote execution are like oil and vinegar. It takes effort to blend them into a tasty vinaigrette, but once you do, you'll never look back to your plain old builds. In this talk, we will introduce the challenges posed by this integration. Various solutions have been proposed over the years. We will explain how we chose one by looking at how these solutions propagate the necessary information across their components. We will then delve into the specifics of our design, explore technical aspects of our deployment, and discuss issues and benefits observed in practice. The last part will focus on performance metrics. We will share our understanding of the impact this change had on our infrastructure and, most importantly, on developers.