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Platform:

Fastly Compute

Language:

Rust

Repo:

https://github.com/fastly/compute-starter-kit-rust-fanout-forward

Use this starter

Using the Fastly CLI, create a new project using this starter somewhere on your computer:

$ fastly compute init --from=https://github.com/fastly/compute-starter-kit-rust-fanout-forward

Or click the button below to create a GitHub repository, provision a Fastly service, and set up continuous deployment:

Setup

The app expects a configured backend named "origin" that points to an origin server. For example, if the server is available at domain example.com, then you'll need to create a backend on your Compute service named "origin" with the destination host set to example.com and port 443. Also set Override Host to the same host value.

You'll also need to enable Fanout on your Fastly service to run this application. To enable Fanout on your service, type:

fastly products --enable=fanout

[!NOTE] This app is not currently supported in Fastly's local development server, as the development server does not support Fanout features. To experiment with Fanout, you will need to publish this project to your Fastly Compute service. using the fastly compute publish command.

Running the application

After deploying the app and setting up the backend configuration, incoming HTTP and WebSocket requests that arrive at the service will be processed by the fetch handler:

1. WebSocket connections will be handed off to Fanout to reach the backend server. Fanout maintains a long-lived connection with the client, and uses the WebSocket-over-HTTP protocol to transform the messages to and from the backend server.

2. HTTP GET and HEAD requests will be handed off to Fanout to reach the backend server. The backend can include GRIP control messages in its response, instructing Fanout to maintain a long-lived connection with the client.

Next Steps

The starter kit is written to send all WebSocket and HTTP GET (and HEAD) traffic to Fanout. In an actual app we would be selective about which requests are handed off to Fanout, because requests that are handed off to Fanout do not pass through the Fastly cache.

For details, see What to hand off to Fanout in the Developer Documentation.

The starter kit code contains a TODO section where you may insert additional conditions to check before setting the use_fanout variable to true.

For example, to check the request for the existence of a certain header:

if let Some(_) = req.get_header("fanout") {
    use_fanout = true;
  }

Notes

The code in this starter kit cannot be used with the fastly::main attribute on the main() entry point. This is because a function decorated with fastly::main is expected to return a response, but handing off to Fanout is an action that does not create a response. Use an undecorated main() function instead, and use Request::from_client() and Response::send_to_client() as needed.

Next steps

Starters are a good way to bootstrap a project. For more specific use cases, and answers to common problems, try our library of code examples.