lambda-mechanic

Lambda Mechanic

Tiny NodeJS server that mocks AWS Lambda requests for local development.

Usage

Install the library and dependencies

% npm install -d lambda-mechanic node-dev

If you're using Typescript you can opt for ts-node-dev

% npm install -d lambda-mechanic ts-node-dev

Create a simple script called server.js with the following content:

const { Mechanic } = require('lambda-mechanic');

// adjust to import your Lambda handler function
import { handler } from './src';

const mechanic = new Mechanic(
  [
    ['/', handler],
    ['/test', async () => ({ statusCode: 200, body: 'Test' })],
  ],
  { port: 3001 },
);

mechanic.listen();

Or for Typescript, create a script called server.ts with the following content:

import { Mechanic } from 'lambda-mechanic';

// adjust to import your Lambda handler function
import { handler } from './src';

const mechanic = new Mechanic(
  [
    ['/', handler],
    ['/test', async () => ({ statusCode: 200, body: 'Test' })],
  ],
  { port: 3001 },
);

mechanic.listen();

In a new terminal window run:

% npx node-dev server.js

Or for Typescript:

% npx ts-node-dev server.ts

You can now experiment with your Lambda handler by sending requests to https://localhost:3000.

API

Mechanic constructor

The Mechanic constructor expects two paramters on instantiation, an array of handler "tuples" and an options object:

new Mechanic(
  handler: HandlerTuple[],
  options: MechanicOptions,
)

HandlerTuple array

The handler "tuple" describes a route and handler function pairing.

Technically it is a Javascript array with a route string (or regular expression) at the first index and a handler function at the second index.

String example:

const handler = async () => ({ statusCode: 200, body: 'Hello World!' });

const route = ['/path', handler];

RegEx example:

const handler = async () => ({ statusCode: 200, body: 'Handles everything...' });

const route = [/.*/, handler];

Handler function

The handler function expects an event that conforms to the Lambda APIGatewayProxyEvent interface and returns a promise that resolves an object that confirms to the APIGatewayProxyResult interface.

If you're using Typescript the types can be imported from the aws-lambda package.

import { APIGatewayProxyEvent, APIGatewayProxyResult } from 'aws-lambda';

const handler = async (
  event: APIGatewayProxyEvent,
): Promise<APIGatewayProxyResult> => ({
  statusCode: 200,
  body: 'Hello World!',
});

MechanicOptions object

There are currently only two options port and headers. The defaults are:

const defaultOptions = {
  port: 3000,
  headers: {},
};

The options interface is:

interface MechanicOptions {
  port?: number;
  headers?: {
    [key: string]: string;
  };
}

Bugs & Issues

If you spot bugs please open an issue.