Developing Serverless Edge Functions with Rust and Deno Deploy: A Beginner’s Guide

Serverless architecture has revolutionized the way developers build scalable applications. Among the popular solutions for deploying serverless applications, Deno Deploy stands out as a powerful platform for creating and deploying edge functions. Combined with Rust, a highly performant and memory-safe programming language, you can build robust serverless solutions that run efficiently at edge locations worldwide.

This guide will walk you through the process of developing serverless edge functions using Rust and deploying them on Deno Deploy. It’s targeted at beginners, so buckle up as we explore the exciting world of serverless computing.

Deno Deploy is a serverless platform built on Deno, a modern JavaScript and TypeScript runtime. It allows developers to run lightweight and performant edge functions across multiple locations, reducing latency and improving the user experience.

Rust is well-known for its performance, safety, and concurrency features. Pairing Rust with Deno Deploy enables developers to leverage Rust’s efficiency for computationally heavy tasks while taking advantage of Deno Deploy’s edge computing capabilities.

Before diving into the implementation, make sure you have the following:

1. Rust Installed: You can install Rust using the official [Rustup](https://rustup.rs/) tool.
2. Deno Installed: Download and install Deno from its [official site](https://deno.land/).
3. Basic Knowledge of JavaScript/TypeScript: Familiarity with scripting languages like JavaScript will help in understanding Deno Deploy.
4. Basic Understanding of Rust: You should have a basic grasp of Rust syntax and concepts like modules, crates, and functions.

Let’s start by creating a simple function in Rust. This function will perform a basic operation, like calculating the factorial of a number.

Below is a simple Rust implementation of a factorial function:

fn factorial(n: u32) -> u64 {
    (1..=n as u64).product()
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_factorial() {
        assert_eq!(factorial(5), 120);
        assert_eq!(factorial(0), 1);
    }
}

Since Deno Deploy executes JavaScript and WebAssembly, we need to compile our Rust code into a WebAssembly (WASM) module.

1. Add the `wasm32-unknown-unknown` target:

“`bash rustup target add wasm32-unknown-unknown “`

1. Set up a new Rust project:

“`bash cargo new rust_to_wasm cd rust_to_wasm “`

1. Add the following dependencies to your `Cargo.toml` file:

“`toml [dependencies] wasm-bindgen = “0.2” “`

1. Modify the Rust code to use `wasm-bindgen`:

   use wasm_bindgen::prelude::*;

#[wasm_bindgen]
pub fn factorial(n: u32) -> u64 {
    (1..=n as u64).product()
}

   

1. Build the project for WebAssembly:

“`bash cargo build –target wasm32-unknown-unknown –release “`

1. Locate the compiled `.wasm` file in the `target/wasm32-unknown-unknown/release` directory.

Once you have your `.wasm` file, the next step is to deploy it using Deno Deploy.

1. Create a new TypeScript file (e.g., `mod.ts`) to load and execute the WebAssembly module:

   <pre class="wp-block-syntaxhighlighter-code">const wasmCode = await Deno.readFile("path_to_your_file.wasm");
const wasmModule = await WebAssembly.instantiate(wasmCode);

const { factorial } = wasmModule.instance.exports;

export default async (req: Request): Promise<Response> => {
  const url = new URL(req.url);
  const query = url.searchParams.get("number");

  if (!query) {
    return new Response("Please provide a number in the query string", { status: 400 });
  }

  const number = parseInt(query);
  const result = factorial(number);

  return new Response(`Factorial of ${number} is ${result}`, { status: 200 });
};
</pre>
   

1. Deploy the function to Deno Deploy:

“`bash deno deploy –project=my-serverless-project “`

1. Test the deployed function by accessing the URL provided by Deno Deploy and passing a query parameter like `?number=5`.

Let’s test the deployed edge function:

1. Open your browser and navigate to the URL provided by Deno Deploy.
2. Append a query string, e.g.: `https://your-deno-deploy-url.netlify.app/?number=5`.
3. Verify the response, e.g., `”Factorial of 5 is 120″`.

Congratulations! You’ve successfully developed a serverless edge function using Rust and Deno Deploy. By compiling Rust into WebAssembly and deploying it to Deno, you’ve created a performant, scalable, and latency-efficient serverless function. As you gain more experience, you can explore advanced use cases, such as connecting your edge function to databases or APIs.

Deno Deploy paired with Rust is a powerful combination for modern applications, offering high performance and global scalability. This guide is just the beginning—feel free to experiment and expand on the concepts covered here.