部署到heroku时，如何使我的node / socket.io应用使用正确的端口？

Question

I followed the online chat tutorial for socket.io where you make a chat application. In my app.js file (I used the express generator) I have...

var port = normalizePort(process.env.PORT || '3000');
app.set('port', port);

This means I need to browse to (and thus my socket server is running from)...

http://localhost:3000

On my page I have the lines...

  var socket = io.connect('http://localhost:3000');
  socket.on('news', function (data) {
    console.log(data);
    socket.emit('my other event', { my: 'data' });
  });

When I run the application locally the socket application works. However to deploy it I used the heroku/node buildpack and when my app is deployed it is running on port 80, so for example is on app.heroku.com. I have two questions...

1) How come my app is on a different port when deployed? (where did this happen?) 2) How do I set my page up to always look at the correct url and port?

Answer 1

var port = normalizePort(process.env.PORT || '3000');
app.set('port', port);

This is fine. Keep in mind that this does nothing, it's just an arbitrarily set value in your app. In order to listen on that port, you must later tell your server to listen, like app.listen(app.get('port')) .

var socket = io.connect('http://localhost:3000');

This is what you want to change, to:

var socket = io.connect();

When you're hosting on Heroku, you aren't connecting to "localhost:3000" (but rather yourapp.herokuapp.com:80, or customdomain.com:80). So, by specifying localhost:3000, you're dooming socket.io to not be able to find its own server.

Answer 2

You should be connecting to port 80 when running through Heroku. If you want the local and Heroku implementations to both work with your client code, then change this:

var port = normalizePort(process.env.PORT || '3000');

to this:

var port = normalizePort(process.env.PORT || '80');

And, make sure that your local installation has privileges to run on port 80. Then, your client can always access it on port 80 either locally or through Heroku.

Or, if it's inconvenient to run locally on port 80 for privilege reasons, then you can leave the port 3000 there for the local installation and configure your local iptable on your local server so that port 80 requests are automatically forwarded to port 3000 where the server process is.

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Heroku uses a shared infrastructure, running many different processes on the same server with each one running on its own port as specified by process.env.PORT that is separately configured for each separate server process.

But, when your specific domain is accessed on port 80, some sort of network infrastructure out in front of the server that your process is run on (probably some sort of router or load balancer) will redirect that port 80 request on your domain to a port process.env.PORT request on the actual server that your process is running on. Thus, two things happen. 1) Multiple server processes can be run on the same server box each on their own unique port and 2) Each separate domain can be accessed on port 80 and that port will be automatically forwarded to whatever port the process is actually running on the actual server box.

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Incidentally, if you change the client code to this:

io.connect();

Then, the client will just connect to whatever port the web page was loaded from (automatically use the same origin) which is pretty much always what you want.