Question: What could be the possible reasons for socket-io server returning 400 Bad Request via nginx?

Hi,

We are facing a scenario where a good percentage of requests going to /Socket.io/?... is returning with 400.

Default nginx access log results are littered with:

10.0.0.82 - - [04/Dec/2015:11:43:27 +0000] "GET /socket.io/?__sails_io_sdk_version=0.11.0&__sails_io_sdk_platform=browser&__sails_io_sdk_language=javascript&EIO=3&transport=websocket HTTP/1.1" 400 45 "-" "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/45.0.2454.101 Safari/537.36"

The requests are not even reaching our overlying SailsJS server. We suspect something going wrong at socket-io layer. Any thought?

[shamasis]

After a LOT of painstaking log-watching, this is our temporary solution for nginx config (to stop freaking out our servers.) The following directive checks for missing “Upgrade” header in request and returns with a 202 without hitting the node server.

location /socket.io {
    set $local_upgrade_failure "${arg___sails_io_sdk_platform}${arg_transport}${connection_upgrade}";
    if ( $local_upgrade_failure = "browserwebsocket" ) { return 202; break; }

 ... remain proxy configurations
}

Now, this does NOT fix the clients that are sending these requests, but surely frees up the server. Now, the question is @rauchg, why are some socket.io clients not sending the “upgrade” header? One pattern is that they are all Windows and a very few Linux machines. Did not spot a single OSX in one full hour of heavy usage.

[shamasis]

I will then have to deep dive into socket.io - it’s being returned by socket.io with no additional message -

{ code: 3, message: “badRequest”}