I didn't find other Rust/musl Docker image setups that I was happy with.
This is as simple as I was able to get working.
The hard part was being able to use the rustls crate.
The underlying problem came from the ring crate, which bundles c and c++ code.
The rmusl.sh script included in this repo just works on macOS,
which is really nice. I expect it to work on a Linux host as well.
It successfully caches crate downloads by sharing the cargo cache directories
between the Docker container and the host system.
By default, rmusl.sh will run
cargo build --release --target x86_64-unknown-linux-musl
in the context of the current working directory.
The output of the build will appear in
target/x86_64-unknown-linux-musl/release/