Can a webapp connect to mosquitto?-CodePudding

I have a mosquitto_sub running on background on serverA, let's say with topic "TEST", port 1883. I followed this to use nginx as a stream proxy to mosquitto, on ServerB.

Testing the setup sending a message to ServerB, using mosquitto_pub, the message is received and displayed correctly on serverA.

Now I'd like that a webapp running on serverC could receive the mqtt messages I send using a websocket, as far as I understand that nginx setup is made exactly for this purpose because browser can't use directly mqtt protocol.

I did two tests:

pointing the websocket to ServerB stream (wss://serverB:1883)
pointing the websocket to nginx reverse proxy with this config:

...
server {
    listen 443 ssl;
    ...

    location /webapp/websocket {
            proxy_set_header HOST $host;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header X-Forwarded-Proto $scheme;
            proxy_pass_request_headers on;
            proxy_pass http://serverB:1883/;
            proxy_http_version 1.0;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection "Upgrade";
            proxy_read_timeout 1800s;
    }

}

With both the websocket doesn't work, with error 502 Bad Gateway. My questions are, did I understand wrong and can it be done? Does it say error 502 just because the webapp must be programmed to specify the topic to listen?

CodePudding user response：

The Mosquitto broker supports MQTT over WebSockets, but it has to be on a separate port to native MQTT over TCP.

So if Mosquitto is normally listening on port 1883, you need to pick a different port to run the MQTT over WebSockets listener. e.g.

listener 1883

listener 8083
protocol websockets

You would then need to update the port in the proxy_pass entry to match.