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Hacker News Hacker NewsIt 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.
What nobody tells you is that the cache mount is local to the builder daemon. If you're running builds on ephemeral CI instances, those caches are gone every build and you're back to square one. The registry cache backend exists to solve this but it adds enough complexity that most teams give up and just eat the slow builds.
The other underrated BuildKit feature is the ssh mount. Being able to forward your SSH agent into a build step without baking keys into layers is the kind of thing that should have been in Docker from day one. The number of production images I've seen with SSH keys accidentally left in intermediate layers is genuinely concerning.
But the real hidden power of buildkit is the ability to swap out the Dockerfile parser. If you want to see that in action, look at this Dockerfile (yes, that's yaml) used for one of their hardened images: https://github.com/docker-hardened-images/catalog/blob/main/...
The code first options are quite good these days, but you can get so far with make & other legacy tooling. Docker feels like a company looking to sell enterprise software first and foremost, not move the industry standard forward
great article tho!
BuildKit is very cool tech, but painful to run at volume
Fun gotchya in BuildKit direct versus Dockerfiles, is the map iteration you loaded those ENV vars into consistent? No, that's why your cache keeps getting busted. You can't do this in the linear Dockerfile
It sounds great in theory, but it JustDoesn'tWork(tm).
Its caching is plain broken, and the overhead of transmitting the entire build state to the remote computer every time is just busywork for most cases. I switched to Podman+buildah as a result, because it uses the previous dead simple Docker layered build system.
If you don't believe me, try to make caching work on Github with multi-stage images. Just have a base image and a couple of other images produced from it and try to use the GHA cache to minimize the amount of pulled data.