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You are holding BUILD files wrong

I’ve heard it from people new to Bazel but also from people very familiar with the Bazel ecosystem: BUILD files must go away. And they must go away because they are redundant: they just repeat the dependency information that’s already encoded in the in-code import/use statements.

Hearing this from newcomers to Bazel isn’t surprising: after all, most newcomers are used to build tools that provide zero facilities to express dependencies across the sources of your own project. Hearing it from old-timers, however, is disappointing because it misses the point of what BUILD files can truly offer.

September 26, 2025 · Tags: bazel, blogsystem5, opinion
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Bazel and glibc versions

Imagine this scenario: your team uses Bazel for fast, distributed C++ builds. A developer builds a change on their workstation, all tests pass, and the change is merged. The CI system picks it up, gets a cache hit from the developer’s build, and produces a release artifact. Everything looks green. But when you deploy to production, the service crashes with a mysterious error: version 'GLIBC_2.28' not found. What went wrong?

September 19, 2025 · Tags: bazel, blogsystem5, unix
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Trusting builds with Bazel remote execution

The previous article on Bazel remote caching concluded that using just a remote cache for Bazel builds was suboptimal due to limitations in what can and cannot be cached for security reasons. The reason behind the restrictions was that it is impossible to safely reuse a cache across users. Or is it?

In this article, we’ll see how leveraging remote execution in conjunction with a remote cache opens the door to safely sharing the cache across users. The reason is that remote execution provides a trusted execution environment for actions, and this opens the door to cross-user result sharing. Let’s see why and how.

September 12, 2025 · Tags: bazel, blogsystem5
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Understanding Bazel remote caching

The previous article on Bazel action non-determinism provided an introduction to actions: what they are, how they are defined, and how they act as the fundamental unit of execution in Bazel. What the article did not mention is that actions are also the fundamental unit of caching during execution to avoid doing already-done work.

In this second part of the series, I want to revisit the very basics of how Bazel runs actions and how remote caching (not remote execution, because that’ll come later) works. The goal here is to introduce the Action Cache (AC), the Content Addressable Storage (CAS), how they play together, and then have some fun in describing the many ways in which it’s possible to poison such a cache in an accidental or malicious manner.

September 5, 2025 · Tags: bazel, blogsystem5
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Bazel and action (non-) determinism

A key feature of Bazel is its ability to produce fast, reliable builds by caching the output of actions. This system, however, relies on a fundamental principle: build actions must be deterministic. For the most part, Bazel helps ensure that they are, but in the odd cases when they aren’t, builds can fail in subtle and frustrating ways, eroding trust in the build system.

This article is the first in a series on Bazel’s execution model. Having explained these concepts many times, I want to provide a detailed reference before explaining a cool solution to a problem I recently developed at work. We will start with action non-determinism, then cover remote caching and execution, and finally, explore the security implications of these features.

This first article explains what non-determinism is, how it manifests, and how you can diagnose and prevent it in your own builds. Let’s begin.

July 21, 2025 · Tags: bazel, blogsystem5
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Lessons along the EndBOX journey

About six months ago, during one of my long runs, I had a wild idea: what if I built an OS disk image that booted straight into EndBASIC, bundled it with a Raspberry Pi, a display, a custom 3D-printed case, and made a tiny, self-contained retro BASIC computer? Fast-forward to today and such an idea exists in the form of “the EndBOX prototype”!

This article isn’t the product announcement though—that’s elsewhere. What I want to do here is look back at the Blog System/5 articles I’ve written over the past months because what might have seemed like scattered topics were actually stepping stones toward the EndBOX.

Let’s look at what I learned along the way and why, even though developing EndBASIC may sound like a “useless waste of time”, it’s a great playground and the source of inspiration for the articles you’ve come to appreciate here.

June 17, 2025 · Tags: blogsystem5, endbasic
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Whatever happened to sandboxfs?

Back in 2017–2020, while I was on the Blaze team at Google, I took on a 20% project that turned into a bit of an obsession: sandboxfs. Born out of my work supporting iOS development, it was my attempt to solve a persistent pain point that frustrated both internal teams and external users alike: Bazel’s poor sandboxing performance on macOS.

sandboxfs was a user-space file system designed to efficiently create virtual file hierarchies backed by real files—a faster alternative to the “symlink forests” that Bazel uses to prepare per-action sandboxes. The idea was simple: if we could lower sandbox creation overhead, we could make Bazel’s sandboxing actually usable on macOS.

Unfortunately, things didn’t play out as I dreamed. Today, sandboxfs is effectively abandoned, and macOS sandboxing performance remains an unsolved problem. In this post, I’ll walk you through why I built sandboxfs, what worked, what didn’t, and why—despite its failure—I still think the core idea holds promise.

June 11, 2025 · Tags: bazel, blogsystem5, sandboxfs
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Beginning 3D printing

Hello readers and sorry for the 2-month radio silence. I’ve been pretty busy at work, traveling during school breaks, hacking on EndBASIC when time permitted, and… as of two weeks ago… tinkering with 3D printing as a complete beginner. So, today, I’d like to walk you through the latter because it has been a really fun and rewarding journey, albeit frustrating at times.

You’d think that to use a 3D printer, you’d design a 3D model and then… just… send it to the printer? That’s almost true, but it ignores the realities of producing a physical object from an “abstract” model: when designing such a model, you need to take into account the limitations of 3D printing and you need to translate your model into something the 3D printer can understand via a process called slicing.

Let’s take a brief peek at all of these steps. I’ll assume you are a complete beginner like I am. The pictures I’ll show are all for a “first project” I did to remake the bars of a bird cage I have, as the birds had fully destroyed the previous ones.

May 28, 2025 · Tags: blogsystem5, hardware
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The next generation of Bazel builds

Today marks the 10th anniversary of Bazel’s public announcement so this is the perfect moment to reflect on what the next generation of build systems in the Bazel ecosystem may look like.

I write this with the inspiration that comes from attending the first ever conference on Buildbarn, one of the many remote execution systems for Bazel. In the conference, Ed Schouten, the creator of Buildbarn, presented Bonanza: a skunkworks reimagination of Bazel for truly large builds.

March 24, 2025 · Tags: bazel, blogsystem5
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Bazel at Snowflake two years in

Two and a half years ago, I joined Snowflake to help their mission of migrating to Bazel. I spent the first year of this period as an Individual Contributor (IC) diving deep into the migration tasks, and then I took over the Tech Lead (TL) role of the team to see the project through completion.

This week, we publicly announced that we completed our migration to Bazel for the largest part of our codebase and we provided details on our journey. I did not publish that article here for obvious reasons, so… today’s entry is going to be a light one: all I want to do is point you at our announcement as well as the various other related articles that came before it.

March 14, 2025 · Tags: bazel, blogsystem5, snowflake
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