Creating an AWS Lambda function with nbb


Nbb is a scripting environment, in the tradition of babashka, but for Node.js. Like babashka, nbb doesn't have a compile cycle, but it just interprets Clojure code using SCI. It has a few useful CLJS libraries included, e.g. for JS interop. It can load any JS library from NPM. Check out the repo here. There are several examples available as well.

Nbb on AWS Lambda

While it was already possible to use nbb on AWS Lambda, it needed some boilerplate code. Valtterri Harmainen captured this boilerplate in his nbb-lambda-adapter.

This week AWS announced that AWS Lambda now supports ES Modules and Top-Level Await for Node.js 14. With that in place, the boilerplate code isn't necessary anymore.

Creating an nbb lambda

All you need to do to get nbb running on AWS Lambda is the following:


{"dependencies": {"nbb": "0.1.0"}}


import { loadFile } from 'nbb';

const { handler } = await loadFile('./example.cljs');

export { handler }


(ns example)

(defn handler [event _ctx]
  (js/console.log event)
  (js/Promise.resolve #js{:hello "world"}))

#js {:handler handler}

Make sure to run npm install.

Zip the directory: zip -r .

Go to the AWS Console. Choose Lambda -> Author from Scratch -> Runtime Node.s 14.x + arm64. The default 128 MB should be sufficient for fast response times after cold start, but for fast cold starts, higher memory (which comes with higher CPU) is better.

Then choose Upload from and choose the zip file.

You can test the lambda function by creating a test event and invoking it.

To be able to invoke the function via HTTP, you'll first have to Publish it.

The API Gateway response has to be a little different so adjust your handler code like this...


(ns example)

(defn handler [event _ctx]
      (js/console.log event)
        (clj->js {:statusCode 200
                  :body       (js/JSON.stringify #js{:hello "world"})})))

#js {:handler handler}

After uploading the updated code, under Configuration > Trigger you can add an API Gateway trigger. Create one and choose HTTP API and Security Open (make sure you change this when it becomes a private production lambda rather than just for the sake of trying nbb on lambda!).

After that you should end up with a public URL like which you can then call from curl or via a browser. The response times I got after the cold start were around 100ms.

As a nice bonus, you can edit the CLJS code directly in the console:

After cold start on a 128MB ARM lambda:

$ time curl
{"hello":"world"}curl 0.02s user 0.01s system 23% cpu 0.105 total

And you get to edit the CLJS code in the console :)

— (λ. borkdude) (@borkdude) January 8, 2022

Also check out this nbb serverless example that Valtteri Harmainen made.

Discuss this post here.

Published: 2022-01-08

Tagged: clojure