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  • VerneMQ / MQTT Introduction
  • Installing VerneMQ
    • Installing on Debian and Ubuntu
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  • Configuring VerneMQ
    • Introduction
    • The VerneMQ conf file
    • Schema Files
    • Auth using files
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    • MQTT Options
    • MQTT Listeners
    • HTTP Listeners
    • Non-standard MQTT options
    • Websockets
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    • Introduction
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  • Live Administration
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  • Misc
    • Loadtesting VerneMQ
    • Not a tuning guide
    • Change Open File Limits
  • Guides
    • A typical VerneMQ deployment
    • VerneMQ on Kubernetes
    • Loadtesting VerneMQ
    • Clustering during development
    • Not a tuning guide
    • Change Open File Limits
    • Migrating to 2.0
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  1. Configuring VerneMQ

Websockets

Configure WebSocket Listeners for VerneMQ.

PreviousNon-standard MQTT optionsNextLogging

Last updated 1 month ago

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VerneMQ supports the WebSocket protocol out of the box. To be able to open a WebSocket connection to VerneMQ, you have to configure a WebSocket listener or Secure WebSocket listener in the vernemq.conf file first:

listener.ws.default = 127.0.0.1:9001

listener.wss.wss_default = 127.0.0.1:9002
# To use WSS, you'll have to configure additional options for your WSS listener (called `wss_default` here):
listener.wss.wss_default.cafile = ./etc/cacerts.pem
listener.wss.wss_default.certfile = ./etc/cert.pem
listener.wss.wss_default.keyfile = ./etc/key.pem

Keep in mind that you'll use MQTT-over-WebSocket, so you will need a Javascript library that implements the MQTT client behaviour. We have used the as well as

You won't be able to open WebSocket connections on a base URL, always add the /mqtt path.

When establishing a WebSocket connection to the VerneMQ MQTT broker, the process begins with an HTTP connection that is then upgraded to WebSocket. This upgrade mechanism means the broker's ability to accept connections can be influenced by HTTP listener settings.

In certain scenarios, such as when connecting from a frontend application, the size of HTTP request headers (including cookies) can exceed the default maximum allowed by VerneMQ. This can lead to a 'HTTP 431 Request Header Fields Too Large' error, preventing the connection from being established.

This behavior is configurable in the vernemq.conf file to accommodate larger headers:

listener.http.default.max_request_line_length=32000
listener.http.default.max_header_value_length=32000
Eclipse Paho client
MQTT.js