How does SST run Go lambdas locally? Can the mechanism expand to include custom lambda runtimes?

Hey @Dennis Dang, SST starts up a local Runtime Server, and the Go lambda function calls the Runtime Api to get the event

There’s another lib in Rust that we’d like to use and still enable the nice live lambda dev feature. Availability in lambdas is essentially our first (and welcomed) constraint.

Ah got it! There are 3 areas of work to implement a new language: 1. in

sst deploy

we need to build the Rust functions; 2. in

sst start

we need to run the Rust functions on request; 3. in

sst start

we need to watch for changes and rebuild the Rust functions quickly I don’t know Rust, but if you could help me on #1, that’d be great. #2 and #3 should be fairly straight forward. For #1, here’s the code for building the Lambda functions - https://github.com/serverless-stack/serverless-stack/blob/master/packages/resources/src/Function.ts#L215-L241 It’s pretty short. Python is built inside Docker; Node and Go are not. We just need to add another case here to handle Rust. Let me know if you want to take a crack at it and submit a PR.

Can I create a gh issue to track work and discussions? Some points to discuss: 1. Supported runtime variable - Rust require the use of the custom AL2 runtime. It’s a constant value available like the other ones but if i add this builder, it doesn’t necessarily mean the rustBuilder will work for other languages. 2. WIP

For sure! Let’s create an issue for this. I’m thinking we define a new runtime name ie.

rust1.x

or something, and you create the function like this:

new sst.Function(this, "MyRustFunction", {
  srcPath: "path/to/Cargo.toml",
  handler: "path/to/lambda.rs",
  runtime: "rust1.x",
});

And internally we will use

provided.al2

runtime to create the lambda function. What do you think?

Perfect I was thinking around that line too. The rust builder api should operate similarly to the Go one.

Yeah, I think it does. If handler is just

src

, it assumes the file is

src/main.go

. But u can specify a different file

src/some_handler.go

with

package main

.

Hey Frank, I found a workaround so we no longer need the Rust implementation! Info is still good to know. Perhaps I'll still do one for Rust or other.

I see. If you guys need Rust runtime again, let me know. It is something on the roadmap.