Consider the following code:

fn main() {
    env_logger::init();
    let sys = actix::System::new("router");
    server::new(|| {
      // Insert `App` declaration here
    }).workers(1)
        .bind("127.0.0.1:8080")
        .unwrap()
        .start();
    let _ = sys.run();
}

We create a new server with the server::new method call that expects a closure to return the App instance. Before we create the App instance, we have to finish our server and run it. The workers method sets the number of threads to run actors.

The next call of the bind method binds the server's socket to an address. If it can't be bound to an address, the method returns Err, and we unwrap the result to halt a server if we can't start a server on a desired port. At the end, we call the start method to start the Server actor. It returns an Addr struct with an address that you can use to send messages to a Server actor instance.

Actually, the Server actor won't run until we call run the method of the System instance. Add this method call, and then we'll go on to look at creating an App instance in detail.