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lambda-emulator

Goal: Test invoking lambda functions locally in a manner that is as close to production as sanely possible.

This is an emulator and not a simulator.

npm install cmawhorter/lambda-emulator --save-dev

Getting started

server.js

var createServer = require('lambda-emulator');
var handler = require('./handler.js');
createServer(handler, 'lambda'); // "lambda" is the scenario to emulate

handler.js

module.exports = function(event, context, callback) {
  console.log('event', event);
  console.log('context will be similar to production', context);
  callback(null, {
    hello: 'world'
  });
};

dev.js

var AWS = require('aws-sdk');
var lambda = new AWS.Lambda({
  endpoint:           'http://localhost:3000', // required
  region:             'local-dev',             // required?
  accessKeyId:        'a',                     // something required
  secretAccessKey:    'b',                     // something required
  maxRetries:         0,                       // optional
});

lambda.invoke({
  // only one handler can be tested per server so this 
  // is largely for logging and making context have something
  // more production-ish
  FunctionName: 'some-function', 
  Payload: JSON.stringify({
    some: 'data',
    goes: true,
    here: {
      now: Date.now(),
    },
  }),
}, (err, data) => {
  console.log(data);
});

Types of servers emulated

Lambda can be invoked in a variety of different ways:

• Manual (API client -> RequestResponse)
• Trigger (event source e.g. SNS)
• Stream (kinesis e.g. kinesis or dynamodb stream)
• API Gateway (which is technically a trigger, which itself is technically RequestResposne with service event, but w/e)

However, at this time, only Manual and API Gateway are supported.

See dev/_handlers.js for examples of each.

Lambda RequestResponse

createServer(handler, 'lambda')

Any regular AWS client properly configured should be able to invoke and work as expected.

API Gateway Proxy

createServer(handler, 'apigateway')

Emulates an API Gateway request and Lambda proxy invocation. Assumes it's proxy is from server root e.g. apigateway.example.com/prod/anything/here/gets/proxied

Not ideal, but works. (PR welcome.) Additionally none of the advanced API Gateway features are implemented (like api keys, transforms, etc. and the upcoming Lambda@Edge)