fasttime

A lightweight Fastly Compute@Edge runtime for running wasm applications locally

about

Fastly allows you to run WASM request within a WASI-based runtime on its edge servers. fasttime implements those runtime interfaces using wasmtime served on a local HTTP server allowing you to run you Compute@Edge applications ✨ locally on your laptop ✨.

🤸 usage

Building your app

The fastest way to get started with Compute@Edge is though the Fastly CLI

$ fastly compute build

If you do not have Fastly CLI, you can also build with the standard cargo tooling. Fastly assumes a Rust toolchain version of 1.46.0

# optionally install the wasm32 toolchain if you have not done so already
$ rustup target add wasm32-wasi --toolchain 1.46.0
# build a release mode .wasm executable
$ cargo +1.46.0 build --release --target wasm32-wasi

To start fasttime, just provide it with the path to your Fastly Compute@Edge .wasm build artifact.

Serving up your app

$ fasttime -w target/wasm32-wasi/release/app.wasm

This starts up a localhost HTTP server listening on port 3000 which you can interact with with an HTTP client like curl

curl -i "http://localhost:3000"

↔️ backends

A common usecase for Fastly is proxying a set of backend hosts referred to by name. fasttime supports providing multiple -b | --backend flags with values of the form {backend}:{host}. By default, if you send a request to a backend that you have not mapped, a bad gateway response will be returned by the server.

$ fasttime -w target/wasm32-wasi/release/app.wasm \
    -b backend-two:localhost:3001 \
    -b backend-two:you.com

📚 dictionaries

A common way to store lookup information in Fastly is to use edge dictionaries. fasttime supports providing multiple -d | --dictionary flags with values of the form {dictionary}:{key}={value},{key2}={value2}.

$ fasttime -w target/wasm32-wasi/release/app.wasm \
    -d dictionary-one:foo=bar \
    -d dictionary-two:baz=boom

🪵 logging

The Compute@Edge runtime supports the notion of remote logging endpoints. These are addressed by name within your applications.

use fastly::log::Endpoint;

let mut endpoint = Endpoint::from_name("endpoint-name");
writeln!(endpoint, "hello {}", "wasm");

fasttime currently support these by logging directly to stdout by default.

🔍 debugging

Set the RUST_LOG env variable to fastime=debug and run the cli as usual

RUST_LOG=fasttime=debug fasttime -w target/wasm32-wasi/release/app.wasm

🚧 roadmap

• tls support
• support config file based configuration
• hot reloading of wasm file

Doug Tangren (softprops) 2020