🚦 Ampel

Ampel is a lightweight, dependency free* load balancer that is tailored to one specific use case. Enjoy. ✨

* Well, almost dependency free. It requires only appmetrics for production in order to easily expose internal Node.js metrics.

Architecture

The design is simple, the process creates a vanilla Node.js HTTP server, and for each incoming request (GET/POST) it opens a connection to the upstream backends using http.request. The request payload and response are elegantly .pipe()'d to each other for simplicity.

Features

✔️ All GET requests are served using a round robin method.
✔️ All POST requests are sent to all upstream backends, with the first responder eventually serving the incoming request.
✔️ Exponential back-off retry interval.
✔️ Exposes Graphite protocol metrics (currently only supports InfluxDB API).

⚠️ No support for HTTPS as of now.

Getting Started

Setup

1. Clone the repository

$ git clone https://github.com/losnir/ampel.git
$ cd ampel

2. Install dependencies

$ npm install

$ yarn

Configuration

Configuration is a simple config.json file under the root of the project. The structure is as follows:

{
  "backends": [
    { "host": "127.0.0.1", "port": "6000" },
    { "host": "127.0.0.1", "port": "6001" },
    { "host": "127.0.0.1", "port": "6002" },
    // etc...
    // port is optional, if left empty then '80' will be used by default.
  ],
  "metrics": {
    "enabled": true,     // Enable metrics reporting?
    "host": "127.0..1"   // InfluxDB host
    "port": "8086",      // InfluxDB port
    "database": "ampel"  // InfluxDB database name
  }
}

Running a Development Build

Ampel is using Babel. There is a special npm script to spin-up a development build with nodemon.

$ npm run start:dev

You can also run with debugging enabled (uses node --inspect on port 5858):

$ npm run start:inspect

Running a Production Build

Run the build npm script to, this will create all build artifacts under /dist.

$ npm run build

And then to run:

$ npm start

You can deploy the application however you like, using forever, pm2, now.sh etc.

Tip: You can use the environment variable PORT to control the port the http server exposes on (by default it is 80):

$ PORT=8080 npm start

Testing 🐈

npm test