Clojurescript on AWS Lambda via Serverless

aws, aws-lambda, clojure, clojurescript, leiningen, nodejs, serverless



Build Status

AWS Lambda is a service which allows named functions to be directly invoked (via a client API), have their execution triggered by a variety of AWS events (S3 upload, DynamoDB activity, etc.) or to serve as HTTP endpoints (via API Gateway).

This README serves to document a Leiningen plugin (lein-cljs-lambda), template (cljs-lambda) and small library (cljs-lambda) to facilitate the writing, deployment & invocation of Clojurescript Lambda functions.

The plugin can deploy functions itself, or the excellent Serverless framework can be used, via serverless-cljs-plugin.


  • Low instance warmup penalty
  • Use promises, or asynchronous channels for deferred completion
  • :optimizations :advanced support, for smaller zip files*
  • Utilities for testing Lambda entrypoints off of EC2
  • Function publishing/versioning
  • Serverless integration

N.B. If using advanced compilation alongside Node's standard library, something like cljs-nodejs-externs will be required


This collection of projects is used extensively in production, for important pieces of infrastructure. While efforts are made to ensure backward compatibility in the Leiningen plugin, the cljs-lambda API is subject to breaking changes.

Recent Changes

  • io.nervous/lein-cljs-lambda 0.6.0 defaults the runtime of deployed functions to nodejs4.3, unless this is overriden with :runtime in the fn-spec or on the command-line. While your functions will be backwards compatible, your AWS CLI installation may require updating to support this change.



Clojars Project


Clojars Project

Get Started

$ lein new cljs-lambda my-lambda-project
$ cd my-lambda-project
$ lein cljs-lambda default-iam-role
$ lein cljs-lambda deploy
$ lein cljs-lambda invoke work-magic \
  '{"spell": "delay-promise", "magic-word": "my-lambda-project-token"}'
$ lein cljs-lambda update-config work-magic :memory-size 256 :timeout 66


To generate a minimal project:

$ lein new serverless-cljs my-lambda-project




Function Examples

(Using promises)

(deflambda slowly-attack [{target :name} ctx]
  (p/delay 1000 {:to target :data "This is an attack"}))

AWS Integration With eulalie

(Using core.async)

This function retrieves the name it was invoked under, then attempts to invoke itself in order to recursively compute the factorial of its input:

(deflambda fac [n {:keys [function-name] :as ctx}]
    (if (<= n 1)
      (let [[tag result] (<! (lambda/request! (creds/env) function-name (dec n)))]
        (* n result)))))

See the eulalie.lambda.util documentation for further details.

N.B. Functions interacting with AWS will require execution under roles with the appropriate permissions, and will not execute under the placeholder IAM role created by the plugin's default-iam-role task.

Further Examples

Using SNS & SQS from Clojurescript Lambda functions is covered in this working example, and the blog post which discusses it.



$ lein cljs-lambda invoke my-lambda-fn '{"arg1": "value" ...}' [:region ...]


If you're interested in programmatically invoking Lambda functions from Clojure/Clojurescript, it's pretty easy with eulalie:

 {:access-key ... :secret-key ... [:token :region etc.]}
 {:arg1 "value" :arg2 ["value"]})


cljs-lambda is free and unencumbered public domain software. For more information, see or the accompanying UNLICENSE file.