Websockets with Socket.io Node apps on Microsoft Azure - node.js

Question

We have a Nodejs server that communicates with the websocket protocol (WebRTC, socket.io).
During our development on Heroku, we did not encounter any particular problem.
However, we encountered problems during the deployment of our application on Azure:
The client / server communication is unstable, after analysis we noticed that there is a failure to communicate in websocket and that the transport protocol used is 'polling':
websocket.js:112 WebSocket connection to
'wss://hote.fr/socket.io/?EIO=3&transport=websocket&sid=EgjKLAtp89wrBKMzAAAG'
failed: Error during WebSocket handshake: Unexpected response code:
503
When you activate the "Websocket" function on the administration, the site becomes even more unstable and very long and communication is impossible. The problem of websocket communication is not solved with this function. Example
After having informed us we did disable the websockets in the web.config but without change.
Note that with the same code, everything works well under heroku and the protocol used is websocket.
Has anyone ever encountered this problem, and has a solution?
I'm sorry about my English.
Thank you in advance for your time.

Answer 1

You need do the following to make it work on Azure App Service.
Enable Web sockets via the Azure portal.
Disable the IIS WebSocket module to allow Node.js to provide its own
WebSocket implementation by add this to your web.config file:
<webSocket enabled="false" />
Tell Socket.IO to use WebSocket only instead of a few XHR requests by adding this to the Node.js server:
io.set('transports', ['websocket']);
And on the client add this:
var socket = io({transports: ['websocket']});

Answer 2

Try the suggestions outlined by Aaron to narrow the issue, I would like to highlight a few restrictions on the Azure Sandbox to help isolate the issue further:
1.In App Service, limits are enforced for the maximum number of outbound connections that can be made for each VM instance.
As mentioned in the document Cross-VM numerical limits:
“These limits apply only for customers of Basic or higher plans; in other words, customers running on their own dedicated VMs. These limits are there to protect the entire VM even though one particular site may be with its limits described above. The limits are different depending on the size of VM configured.”
This error also might occur if you try to access a local address from your application.
As mentioned in the document Local address requests:
“Connection attempts to local addresses (e.g. localhost, 127.0.0.1) and the machine's own IP will fail, except if another process in the same sandbox has created a listening socket on the destination port.
Rejected connection attempts, such as the following example which attempts to connect to 127.0.0.1:80, from .NET will result in the following exception:
Exception Details: System.Net.Sockets.SocketException: An attempt was made to access a socket in a way forbidden by its access permissions 127.0.0.1:80.”
3.For more information about outbound connections in your web app, see the blog post about outgoing connections to Azure websites.