[kylegalbraith]

After building Depot [0] for the past three years, I can say I have a ton of scar tissue from running BuildKit to power our remote container builders for thousands of organizations.

It looks and sounds incredibly powerful on paper. But the reality is drastically different. It's a big glob of homegrown thoughts and ideas. Some of them are really slick, like build deduplication. Others are clever and hard to reason about, or in the worst case, terrifying to touch.

We had to fork BuildKit very early in our Depot journey. We've fixed a ton of things in it that we hit for our use case. Some of them we tried to upstream early on, but only for it to die on the vine for one reason or another.

Today, our container builders are our own version of BuildKit, so we maintain 100% compatibility with the ecosystem. But our implementation is greatly simplified. I hope someday we can open-source that implementation to give back and show what is possible with these ideas applied at scale.

[0] https://depot.dev/products/container-builds

[skrtskrt]

> It's a big glob of homegrown thoughts and ideas. Some of them are really slick, like build deduplication. Others are clever and hard to reason about, or in the worst case, terrifying to touch.

This is true of packaging and build systems in general. They are often the passion projects of one or a handful of people in an organization - by the time they have active outside development, those idiosyncratic concepts are already ossified.

It's really rare to see these sorts of projects decomposed into building blocks even just having code organization that helps a newcomer understand. Despite all the code being out in public, all the important reasoning about why certain things are the way they are is trapped inside a few dev's heads.

[mikepurvis]

As someone who has worked in the space for a while and been heavily exposed to nix, bazel, cmake, bake, and other systems, and also been in that "passion project" role, I think what I've found is that these kinds of systems are just plain hard to talk about. Even the common elements like DAGs cause most people's eyes to immediately glaze over.

Managers and executives are happy to hear that you made the builds faster or more reliable, so the infra people who care about this kind of thing don't waste time on design docs and instead focus on getting to a minimum prototype that demonstrates those improved metrics. Once you have that, then there's buy-in and the project is made official... but by then the bones have already been set in place, so design documentation ends up focused on the more visible stuff like user interface, storage formats, etc.

OTOH, bazel (as blaze) was a very intentionally designed second system at Google, and buildx/buildkit is similarly a rewrite of the container builder for Docker, so both of them should have been pretty free of accidental engineering in their early phases.

[nl]

> This is true of packaging and build systems in general. They are often the passion projects of one or a handful of people in an organization

This is a very insightful comment

[mikepurvis]

I introduced Depot at my org a few months ago and I've been very happy with it. Conceptually it's simple: a container builder that starts warm with all your previously built layers right there, same as it would be running local builds. But a lot goes into making it actually run smoothly, and the performance-focused breakdown that shows where steps depend on each other and how much time each is taking is great.

It's clear a ton of care has gone into the product, and I also appreciated you personally jumping onto some of my support tickets when I was just getting things off the ground.

[kylegalbraith]

Thank you for the very kind words and for your support. Depot is full of incredible people who love helping others. So while you might see me on a ticket from time to time, it’s really an entire team that is behind everything we do.

[tuananh]

Thanks for the insight Kyle. If Depot can open-source it, that would be amazing for the community.

[kylegalbraith]

Thank you for the post! It’s well done and you captured a lot of the concepts in BuildKit in an easy to understand way. Not an easy thing to do at all.

[dewey]

Looks very interesting, am I reading it correctly that this is only available on AWS for "bring your own compute"?