Fast multi-arch Docker build for Rust projects
Rust allows programs to run very fast and memory efficient, but it has a cost – compile time. In web development, it is standard practice to deliver programs as Docker images and then run them in Kubernetes / Amazon ECS / Docker Compose / etc. After the popularity of ARM processors in recent years, programmers have been faced with the additional step of preparing multi-arch Docker images (meaning that the same image should be able to run natively on both x86-64/amd64 and aarch64/arm64 processors).
Preparing Docker images for interpreted languages is usually not a problem – Docker Buildx is used, which in turn runs inside the emulator and builds the image for each architucture natively. NodeJS / Python just install dependencies via npm / pip, copy the project code, does a little polishing and that's pretty much it. Even in compiled Go this approach works fine because Go has an extensive standard library. In the case of Rust, compiling even a simple web application is a rebuilding of the “universe” – almost any web application requires: HTTP-server, HTTP-client (which in turn requires a library to work with cryptography for https), asynchronous runtime (tokie, etc), serialization/desirialization (serde, serde_json); which in Rust should be installed as external libraries (crates) and should be compiled each time when program builded.
Although Rust compiler has a lot of work to do, it can do it quickly. Even not strongest CI, will build an average project in a couple of minutes. However, this is true only in case of building on native architecture (for example building amd64 binary on an amd64 processor). As soon as we need to build a multi-arch image, we have to do emulation and the compilation speed drops dramatically. For example, on my simple public project – ghstats, building multi-arch image from scratch took about 50 minutes, when same build for native architecture takes 2-3 minutes.
