CLJS in AWS Lambda Quick Start

cljs-serverless.md

CLJS in AWS Lambda Quick Start

Setup

First, a few dependencies:

1. Leiningen: https://leiningen.org/
2. Node.js & NPM: https://nodejs.org/
3. Serverless: https://serverless.com/
4. An active AWS account: https://aws.amazon.com/

Second, take the time to go through the guides on the Serverless website for configuring AWS Lambda and the serverless CLI. It would probably be a good idea to create a simple project and deploying it before going through this guide.

Create our application

lein new figwheel-node cljs-lambda-fn

cd cljs-lambda-fn

npm i

serverless create --template aws-nodejs

core.cljs:

(ns cljs-lambda-fn.core
  (:require [cljs.nodejs :as nodejs]))

(nodejs/enable-util-print!)

;; (defn -main []
;;   (println "Hello world!"))

;; (set! *main-cli-fn* -main)

(defn greet [event ctx cb]
  ;; see `handler.js` generated by serverless
  ;; for reference to `cb` signature
  (cb nil (clj->js
       {:statusCode 200
        :headers {"Content-Type" "text/html"}
        :body "<h1>Hello, world!</h1>"})))

(set! (.-exports js/module) #js
      {:greet greet})

Build: lein cljsbuild once

Test in a Node.js REPL:

$ node
> require('./server.js').greet(null, null, (_, v) => console.log(v))
{ statusCode: 200,
  headers: { 'Content-Type': 'text/html' },
  body: '<h1>Hello, world!</h1>' }
undefined

Configuring Serverless

In serverless.yml, edit these fields:

service: cljs-lambda-greet # something unique
...

functions:
  hello:
    handler: server.greet
    events:
      - http:
          path: greet
          method: get

Deploying

$ serverless deploy
Serverless: Packaging service...
Serverless: Excluding development dependencies...
Serverless: Creating Stack...
Serverless: Checking Stack create progress...
.....
Serverless: Stack create finished...
Serverless: Uploading CloudFormation file to S3...
Serverless: Uploading artifacts...
Serverless: Uploading service .zip file to S3 (2.15 MB)...
Serverless: Validating template...
Serverless: Updating Stack...
Serverless: Checking Stack update progress...
..............................
Serverless: Stack update finished...
Service Information
service: cljs-lambda-greet
stage: dev
region: us-east-1
stack: cljs-lambda-greet-dev
api keys:
  None
endpoints:
  GET - https://mw0r86y2s3.execute-api.us-east-1.amazonaws.com/dev/greet
functions:
  hello: cljs-lambda-greet-dev-hello

$ curl https://mw0r86y2s3.execute-api.us-east-1.amazonaws.com/dev/greet
<h1>Hello, world!</h1>%

Success!!

Thank you! I can't believe how hard it is to get this stuff working.

Can you please show how to make greet work for API Gateway and maybe echo input body? I'm specifically interested in async computation.