Microservices Example With Express And SenecaJS

So, you've heard all the hype about microservices and want to try them. But what to start from? Which tools to choose? How to set up communication between things? Here is an example with well known ExpressJS as HTTP-server and SenecaJS as microservice framework

The Diagram

Our clients (maybe React or Angular frontends) will make HTTP requests to the gateway, which is a simple HTTP-server application. The Gateway, in turn, will communicate to Seneca microservices via message queue. Each microservice will have its own data storage.

express+seneca application diagram

The Tools

We will use well-known tools:

  • ExpresJS as http-server to handle incoming requests and pass them as messages to the microservices, so we are calling it the Gateway
  • RabbitMQ as the Message Queue (bus)
  • SenecaJS as microservice framework
  • MongoDB as data storage

Setting up the Gateway

All our gateway needs to do is to

  1. accept an HTTP request,
  2. post the correspondent message to the message queue,
  3. wait for the response from message queue (which will be posted there by a microservice) and finally
  4. return the HTTP response with relevant data.

The incoming requests will be authorized via one of the microservices (the Auth microservice).

ExpressJS is one good server for these tasks, but it can be any NodeJS http-server actually. Detailed tutorial on how to create an HTTP-server with ExpressJS falls out of scope of this article -- there are hundreds of them in the Internet. We'll focus only on the crucial parts of our system.

Imagine we have to handle user registration requests like this one (cURL format):

curl -i -X POST -d '{"email":"test@user.com","name":"Test User"}' \
'http://api.gateway.com/users'

Essentially we need to handle POST-request with some JSON data on the route http://api.gateway.com/users here. The ExpressJS router code for this could look like this:

const express = require('express');

let router = express.Router();

router.post('/users', function (req, res, next) {
    seneca.act({
        role: 'user',
        cmd: 'register',
        email: req.body.email,
        name: req.body.name
    }, (error, response) => {
        if (error) return next(error);
        res.status(200).send(response);
    })
});

... to be continued

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