This is a minimal rust build pack for Heroku. The build pack will look for the existence of a Cargo.toml file in your project root, if it finds one will perform the following.

• Install rustup
  • This will use curl https://sh.rustup.rs -sSf >> ru.sh to get the install script
  • Once this has completed it will run ru.sh -y
• Updates the path to include cargo
  • export PATH="$PATH:~/cargo.bin"
• It will then extract your application's name from the Cargo.toml file
  • It does this by looping over each line and looking for the first one that begins with "name = "
  • Once found it removes this prefix
• It will run cargo build --release
• Once the application is compiled it will move the result into the root directory as RUSTAPP
  • mv $1/target/release/[app name] ./RUSTAPP
  • The app name is what we captured from the Cargo.toml file
  • This is done to avoid any issues with path resolution
    • cargo run will allow you to use paths relative to the crate root but executing directly from the target directory will fail to resolve the same paths
• Upon release it will attempt to start the application as a web service

It is important to bind your web server to 0.0.0.0 instead of 127.0.0.1.

Another important part about getting a rust webserver working on Heroku is to bind it to the correct port. Heroku will set an env variable $PORT and it will expect your to bind to that within 60 seconds of running the release script.

To get this value you would do the following.

use std::env::var;
fn main() {
    if let Ok(port) = var("PORT") {
        let addr = format!("0.0.0.0:{}", port).parse().expect("Unable to parse port");
        //Start your server
    }
}