by mike_hearn | 2025-08-20 09:25:54+00:00
I've investigated this idea in the past. It's an obvious one but still good to have an article about it, and I'd not heard of Taskcluster so that's cool.

My conclusion was that this is near 100% a design taste and business model problem. That is, to make progress here will require a Steve Jobs of build systems. There's no technical breakthroughs required but a lot of stuff has to gel together in a way that really makes people fall in love with it. Nothing else can break through the inertia of existing practice.

Here are some of the technical problems. They're all solvable.

• Unifying local/remote execution is hard. Local execution is super fast. The bandwidth, latency and CPU speed issues are real. Users have a machine on their desk that compared to a cloud offers vastly higher bandwidth, lower latency to storage, lower latency to input devices and if they're Mac users, the fastest single-threaded performance on the market by far. It's dedicated hardware with no other users and offers totally consistent execution times. RCE can easily slow down a build instead of speeding it up and simulation is tough due to constantly varying conditions.

• As Gregory observes, you can't just do RCE as a service. CI is expected to run tasks devs aren't trusted to do, which means there has to be a way to prove that a set of tasks executed in a certain way even if the local tool driving the remote execution is untrusted, along with a way to prove that to others. As Gregory explores the problem he ends up concluding there's no way to get rid of CI and the best you can do is reduce the overlap a bit, which is hardly a compelling enough value prop. I think you can get rid of conventional CI entirely with a cleverly designed build system, but it's not easy.

• In some big ecosystems like JS/Python there aren't really build systems, just a pile of ad-hoc scripts that run linters, unit tests and Docker builds. Such devs are often happy with existing CI because the task DAG just isn't complex enough to be worth automating to begin with.

• In others like Java the ecosystem depends heavily on a constellation of build system plugins, which yields huge levels of lock-in.

• A build system task can traditionally do anything. Making tasks safe to execute remotely is therefore quite hard. Tasks may depend on platform specific tooling that doesn't exist on Linux, or that only exists on Linux. Installed programs don't helpfully offer their dependency graphs up to you, and containerizing everything is slow/resource intensive (also doesn't help for non-Linux stuff). Bazel has a sandbox that makes it easier to iterate on mapping out dependency graphs, but Bazel comes from Blaze which was designed for a Linux-only world inside Google, not the real world where many devs run on Windows or macOS, and kernel sandboxing is a mess everywhere. Plus a sandbox doesn't solve the problem, only offers better errors as you try to solve it. LLMs might do a good job here.

But the business model problems are much harder to solve. Developers don't buy tools only SaaS, but they also want to be able to do development fully locally. Because throwing a CI system up on top of a cloud is so easy it's a competitive space and the possible margins involved just don't seem that big. Plus, there is no way to market to devs that has a reasonable cost. They block ads, don't take sales calls, and some just hate the idea of running proprietary software locally on principle (none hate it in the cloud), so the only thing that works is making clients open source, then trying to saturate the open source space with free credits in the hope of gaining attention for a SaaS. But giving compute away for free comes at staggering cost that can eat all your margins. The whole dev tools market has this problem far worse than other markets do, so why would you write software for devs at all? If you want to sell software to artists or accountants it's much easier.