Two Express "app"s in one NodeJS server?

Question

I want to be able to pass different requests through different Express middleware stacks.

I think I need two express apps, and some way to branch. e.g.:

var app = express();
var alt_app = express();

app.use(logger('dev'));
app.use(bodyParser.json());

app.use(function(req, res, next) {
  if (some_condition(req)) {
    divert_request_to_alt_app();
  } else {
    next();
  }
}

app.use(middleware_that_must_not_affect_alt_app());
alt_app.use(middleware_that_only_affects_alt_app());

Is such a strategy possible?

If so, what should divert_request_to_alt_app() be?

If not, what are other approaches?

When you say "one NodeJS *server*" do you really mean "one NodeJS *process*"? Assuming you mean process, here's an [example](http://nerdpress.org/2012/04/20/hosting-multiple-express-node-js-apps-on-port-80/) of how you can host multiple apps under a single process. — James, Apr 22 '15 at 12:31
Have you tried using the [node http proxy](https://github.com/nodejitsu/node-http-proxy)? — SivaDotRender, Apr 22 '15 at 12:35
@BenFortune No, routing to the alt_app depends on only the hostname, at the moment, but I may need it to depend on other parts of `req`. — fadedbee, Apr 22 '15 at 12:42
@chrisdew have a look at the example I posted, it shows how you can route different requests to different express instances based on host name. — James, Apr 22 '15 at 13:33
@James the vhost example looks like it is not for express 4.x - the post is dated 2012. There are confusingly two vhost modules on npm. — fadedbee, Apr 22 '15 at 14:18

score 8 · Accepted Answer · answered Apr 22 '15 at 14:48

I found that express apps are functions. Calling them with (req, res, next) is all you need to do to pass a request from one app to another.

In the example below, I have one root app app and two branches app0 and app1.

var app0 = require('./app0');
var app1 = require('./app1');

var app = express();
...
app.use(function(req, res, next) {
  if (some_condition_on(req)) {
    app0(req, res, next);
  } else {
    app1(req, res, next);
  }
});

Two Express "app"s in one NodeJS server?

1 Answers1