How to Use Rust WASM for Serverless Functions (Cloudflare Workers, Fastly)

You use Rust WASM for serverless functions by compiling your code to the wasm32-unknown-unknown target and exporting a handler function that processes requests and returns responses.

rustup target add wasm32-unknown-unknown
cargo build --target wasm32-unknown-unknown --release

1. Create a library crate with default-features = false in Cargo.toml to remove unsupported dependencies like mio.
2. Define an async handler function (e.g., app) that takes a Request and returns a Response using a router like axum.
3. Compile the library to WebAssembly using cargo build --target wasm32-unknown-unknown --release.
4. Upload the generated .wasm file from target/wasm32-unknown-unknown/release/ to your serverless provider (Cloudflare Workers or Fastly Compute@Edge).
5. Configure the provider to invoke your exported function (e.g., app) as the entry point for incoming HTTP requests.

Using Rust WASM for serverless functions turns your code into a tiny, fast file that runs in the browser or on edge servers without needing a full operating system. You write your logic once, compile it to a special format, and upload it to handle web traffic instantly. Think of it like baking a cake and sending just the slice to a party instead of the whole oven.