[asdkhadsj]

Oh yea, I wasn't picking on Rust. If anything I tend to defend Rust haha.

As far as what we did to cache, nothing fancy - using Docker build layers. I add my Cargo files (lock/toml), include a stub source lib.rs or main.rs to make it build with a fake source, and then build the project.

This builds all the dependencies. It also builds a fake binary/lib for your project, so you need to strip that from the target directory. Something like `rm -rf target/your?project?name*` (I use ? to wildcard _ and -)

If you do that in one layer, your dependencies will be cached with that docker image. In the next layer you can add your source like normal, compile it, and you'll be set.

We lose our cache frequently though because we're not taking special care to centralize or persist the layer cache. We should, for sanity.

[giovannibonetti]

> We lose our cache frequently though because we're not taking special care to centralize or persist the layer cache. We should, for sanity.

Do you use digests (@sha256:...) in the Dockerfile source image (FROM ...) to ensure you are always using the same layer?

If not, that is probably the reason why your cache is falling so often.

[asdkhadsj]

Nope, but that shouldn't be required I'd think? It's not locally, for example - as long as each layers resulting hash has not changed the cache is reused. Likewise on CI, if I repeatedly build the caches never miss, it works great. It's more a problem of sometimes, after a days or a week, the layers seem to be gone. But never in-between your pushes to a PR, for example, those always seem to stay.

I think that's happening is our garbage collection on old docker layers is being too aggressive. But because it works so well between commits, pushes to CI and etc - I don't worry about it. The majority of the time I want a cache to work, it works. So it's been a low priority thing for me to fix haha.

edit: Oh, and I forgot, we may have CI jobs running on different machines. Which of course would also miss caches, since we're not persisting the layers on our registry. I'm not positive on this one though, since like I said it never seems to fail between commit pushes _(say to a PR during review, dev, etc)_. /shrug