aws-lambda-config

A module to provide config (JSON document) to AWS Lambda functions

Motivation

AWS Lambda environment variable values do not allow commas (what?) and thus cannot support a robust JSON document for function config; they also don't support native JSON documents (only support a string that could be parsed into JSON). But JSON-ish support can be achieved by encrypting the value (which might be desired anyway), so the commas are not included in the "value". This small library wraps the concerns above (decryption + JSON parsing) into a single call that allows the client function to simply deal with a JSON config document.

If your Lambda function config a) does not need to be encrypted and b) fits neatly into key-value pairs (i.e. not a nested document), it is recommended to avoid this module and simply use Lambda Environment Variables directly. There is some overhead in both processing time and cost for using the KMS key - so if your function does not need it, don't add that overhead.

Usage

1. Include a valid JSON document in an environment variable for your Lambda function, and encrypt it using a KMS key. Alternatively, use the command-line tool to upload new or updated config to an existing function.
2. From your Lambda function, call either getConfig (a config file is required) or getOptionalConfig (no error if the config file is missing) and get the config back as a JSON object.

var conf = require('aws-lambda-config');

exports.handler = function(event, context) {
  conf.getConfig(context, function(err, config) {
    if (!err) {
      console.log(JSON.stringify(config));
    }
  });
}

Design Decisions

Promises

Yes, Promises are much preferred over callbacks. But I decided to implement this using callbacks because it allows people to use it either with callbacks or Promises (by promisifying it using something like Bluebird, which is what I personall will do when using this in other projects). Plus, callbacks simplify the code and tests here.

Config JSON

Recommended best practice is to keep the config JSON checked in to a code repository with the Lambda function (or in a central config repo). Because of this, the included command line tool expects the config JSON to be loaded from a file in your file system. To encourage this, there is not a config parameter that accepts the JSON string directly.

License

Copyright 2016 Gilt Groupe, Inc.

Licensed under the Apache License, Version 2.0: http://www.apache.org/licenses/LICENSE-2.0