ExpressJS as an Orchestration layer? - node.js

Question

How would one use ExpressJS as an orchestration layer?
I have five NodeJS / ExpressJS "API applications" for different business functions (security, human resources, asset management, fleet management, etc.). Each provides raw object / document APIs and has its own database, app server, routes, etc.. I would like to build ANOTHER ExpressJS application to sit IN FRONT OF those five "stacks" and provide higher-level business operations (ie, TerminateEmployee, etc.) by funneling multiple calls into the other five stacks via REST.
Am I insane? Is this common? Maybe I don't know what to search for, but I'm not finding any examples of doing this.
BTW: I'm also thinking of building highly-reusable "widgets" (basically, individual AngularJS services and UI elements) to call into that sixth front-end stack.

Answer 1

Whoa, an old question left unanswered.
SOA, Microservice, or whatever the name is only the abstract thought of system architecture, they need to be applied, now let us define the problem
Problem: need orchestration for middleware
Parameter: we need to define what middleware need to be run (maybe a String for service name and Number for service port) and this value need to be passed as CLI args or process.env
First we need to store our parameter in JS readable format, could be an Array or Object, in my case i need to run multiple service at one port and the app need to be exposed in multiple port eg:
from String
graphql:80 auth:5000 usercrud:5000 trx:6969 docs:4000
to JSON
{
"80":["graphql"],
"5000":["auth", "usercrud"],
"6969":["trx"],
"7070":["ssr"],
"4000":["docs"]
}
we can make CLI accept args by using the popular yargs, but also need to be able read from string passed from .env file, when parsing a string this is quite easy since we can control the format of the string by simply using String.split() function we can make an Array, i prefer using space when separating context (in this case a middleware/service) followed by : and port of this particular service, like auth:5000 and then from this Array we can map the value to an Object (note "5000":["auth", "usercrud"] is sharing the same port so we need to accommodate this two service).
from this config we can iterate the keys which is reflected by its port, so doing Object.keys(service) return an Iterable/Array that we can Map/ForEach according to modern EcmaScript standard. In each iteration we make
app.use(require(`./service/${service[port]}`))
http.createServer(app)
.listen(port, () =>
log(`http://127.0.0.1:${port} >>> ${service[port]}`)
)
usually when we http.createServer(app) we do this once, but now we do it as many as the port we need to exposed, this increased atomicity and decrease dependency inter services.
advantage of this approach is:
can share library / helper
single codebase & consistency
single container development / staging / integration test
controlled service based on resource consumption (not only task, if one of the service is idle / consuming very little resource we can join it with the other service)
up & running source: https://github.com/nsnull0/eService/blob/master/packages/%40nodejs-express/index.js