Yemma-Discovery

Yemma-Discovery is a thin layer to help you manage your nodes in a micro-services architectures maintained in a Registry by Yemma

Either your application represent a micro-service, either your application is a Gateway and wants to access a node with some specifications.

1. Install Yemma-Discovery

npm i --save yemma-discovery

2. To register yourself as a service

Yemma-Discovery automatically register itself as a service as soon as it is instanciated.

Before registering yourself, Yemma-Discovery will look into some environment variables:

# Related to the registry
YEMMA_URI=http://localhost.com:9000 #required information about where the registry is hosted
YEMMA_TOKEN=ytoken                  #since the registry is a yemma application it will verify each request with a token (set during yemma configuration)

# Related to the node itself
REALM=admin                          #required to tell the registry for which part of the business the node is responsible
PORT=3030                            #required also, the port where the node is listening
ACCESS_TOKEN=xF%eeT$mbS&             #required also, the secret used to ensure only trusted issuer can make requests
HOST=customHost.org                  #[optional] if the node is behind a proxy, you can set a host, if not, the registry will try to resolve the node'ip address during registration.

const DisoveryService = require('yemma-discovery');
new DiscoveryService(); // will automatically register the node to the registry

That's it, you are now discoverable from the registry.

You can disable this behavior by passing an option in the constructor. Meaning you don't have to set information related to the node itself.

const DisoveryService = require('yemma-discovery');
new DiscoveryService({ heartBeats: false }); // disable the heartbeat

2.1 Ensuring the request issuer is valid In a typical express server type you can use Yemma-Discovery to validate request issuers are allowed to access your API.

cons express = require('express');
const DisoveryService = require('yemma-discovery');

const server = express();
const ds = new DiscoveryService(); // will automatically register the node to the registry

server.use((req, res, next) => {
    const access_token = req.header('access-token');
    ds.validateIssuer(access_token);
        .then(() => next())
        .catch(() => res.status(403).send('invalid.issuer'));
});

server.get('/', (req, res) => res.send('hello, world'));
server.listen(3000);

3. Proxy request to registered instances.

If you develop a Gateway, it can be helpful to have a direct access to the registered nodes.

const DisoveryService = require('yemma-discovery');
const registry = new DiscoveryService({ heartBeats: false }); // disable the heartbeat

const express = require('express');
const server = express();

server.use(proxy);

function proxy(req, res, next) {
    const components = req.originalUrl.split('/')
    const realm = components[1];

    registry
        .next({realm: realm})
        .then(instance => instance.request('/api/users'))
        .then(response => {
            res.headers = response.headers;
            res.status(response.status(response.statusCode).send(response.data);
        })
        .catch(response => {
            res.status(response.statusCode).send(response.data);
        });
}

server.listen(3000);
console.log('Gateway listening on port 3000');