These are good questions! Here's some answers from the corner of the world I know best as a Wasmtime contributor at Fastly:
1. Spidermonkey.wasm is the basis of Fastly's JavaScript on Compute@Edge support. We have found it to be faster than QuickJS. The source code is here: https://github.com/fastly/js-compute-runtime.
3. Fastly's multi-tenant platform is closed source, but our single-tenant local development platform, which also uses wasmtime under the hood as well, is open source: https://github.com/fastly/viceroy. It isn't a big leap to make viceroy multi-tenant: Wasmtime provides everything you need, and all Viceroy would have to do is dispatch on e.g. HTTP host header to the correct tenant. Our multi-tenant platform is closed source because it is very specialized for use on Fastly's edge, not because the multi-tenant aspect is special.
Nice, the fact that Fastly is comfortable betting on Spidermonkey.wasm is the vote of confidence I needed to dig in! Also really love seeing how much Fastly is giving back to open source!
> 1. Spidermonkey.wasm is the basis of Fastly's JavaScript on Compute@Edge support.
How difficult is staying up to date with SpiderMonkey's latest or pre-release upstream versions? Do have to maintain your own SpiderMonkey patches to make upstream work for you?
We worked with Igalia to upstream the SpiderMonkey patches required to build for wasm32-wasi. We point to a fixed version (see: https://github.com/fastly/spidermonkey-wasi-embedding) which we haven't updated for a minute.
1. Spidermonkey.wasm is the basis of Fastly's JavaScript on Compute@Edge support. We have found it to be faster than QuickJS. The source code is here: https://github.com/fastly/js-compute-runtime.
2. Fastly Compute@Edge is built on wasmtime. You can develop web services for it in Rust, JS, and Go: https://developer.fastly.com/learning/compute/
3. Fastly's multi-tenant platform is closed source, but our single-tenant local development platform, which also uses wasmtime under the hood as well, is open source: https://github.com/fastly/viceroy. It isn't a big leap to make viceroy multi-tenant: Wasmtime provides everything you need, and all Viceroy would have to do is dispatch on e.g. HTTP host header to the correct tenant. Our multi-tenant platform is closed source because it is very specialized for use on Fastly's edge, not because the multi-tenant aspect is special.