Lachesis

Lachesis is a simple timer queue server using NodeJS and MongoDB for persistence.

Usage

Lachesis can be cloned and used as a standalone server, or used as a module.

• Requests can be sent to Lachesis to create / read / update / delete timers through a REST API.
• Timers are evaluated locally in a queue on the server and stored for persistence in MongoDB.
• On expiration, a timer will send a callback containing a data payload to a URL indicated in it's creation.

Limitations and Future Improvements

• Timers currently fire their callback once and are removed. The next version will evaluate whether or not the callback was recieved and retry timers that were not recieved.
• As of the current version CORS is the only provided method of authentication. More robust security can be achieved currently by using the TimerController from the Lachesis module and writing custom routes to call it's functions. This may be integrated into later versions.
• Lachesis does not support filtering. Later versions may include this.

Installation

Standalone Server

git clone [email protected]:abrisene/lachesis.git
touch .env
npm install
npm run start

Server Module

const lachesis = require('lachesis');
const port = 8080; // This can be defined here, or through a .env file.

const start = async () => {
  const timerServer = await lachesis.init(true, port); // This initializes Lachesis and indicates that we want a server with our indicated port.

  // The timer controller can be accessed directly once lachesis has been initialized whether or not we're using a server:
  await timerServer.timerController.createTimer({
    duration: 900,                          // Seconds by default
    payload: { message: 'Timer Done!' },    // This is sent to the callbackUrl
    callback: 'http://localhost:8081'       // The callback url
  });
};

start();

Environment Variables

Lachesis looks for the environment variables below in an .env file in the app's root directory:

Basics

PORT              // Port for the http Server, Passed to Express.
CORS_URLS         // An array of URLS which should be enabled for CORS. Will enable CORS universally if set to '*'

Databases

Lachesis requires a connection to MongoDB to store timers persistently. Credentials to connect to the database must be provided in one of the following ways:

MONGODB {         // An optional JSON object containing redis credentials.
  "url"           // URL of the mongoDB database.
}

MONGODB_URL       // A URL to a mongoDB database.
MONGODB_URI       // A URL to a mongoDB database.
PROD_MONGODB      // A URL to a mongoDB database. This value is populated by Heroku's Mongo Lab addon.

API

Create

To CREATE send a POST request to the /timer route. This will return the created timer with it's id.

Supported Parameters:

{
  startTS         // The timestamp that the timer should begin at. Will default to Date.now()
  endTS           // The timestamp that the timer should expire at. This is required if duration is not set.
  duration        // The duration of the timer. Setting this will automatically set the endTS based off of the startTS + duration.
  durationType    // The time unit of the duration - seconds 's', or milliseconds 'ms'. Defaults to 's' (seconds).
  payload         // An object containing data to be returned when the timer expires.
  callback        // The callback URL. The payload will be sent back with a POST request when the timer expires.
}

Read

To READ send a GET request to the /timer/:id route. This will return the timer and it's associated metadata.

Update

To UPDATE send a PATCH request to the /timer/:id route. This will return the updated timer.

Supported Parameters:

{
  startTS         // The timestamp that the timer should begin at. Will default to Date.now()
  endTS           // The timestamp that the timer should expire at. This is required if duration is not set.
  adjust          // An amount of time to adjust the timer by. This can be used to add or subtract remaining time from the timer.
  duration        // The duration of the timer. Setting this will automatically set the endTS based off of the startTS + duration.
  durationType    // The time unit of the duration or the adjust interval - seconds 's', or milliseconds 'ms'. Defaults to 's' (seconds).
  payload         // An object containing data to be returned when the timer expires.
  callback        // The callback URL. The payload will be sent back with a POST request when the timer expires.
}

Delete

To DELETE send a DELETE request to the /timer/:id route.

This will return the deleted timer. The timer will be deleted immediately and it's callback will NOT be fired.