Message Queuing Telemetry Transport (MQTT)

The mqtt node-type uses [libmosquitto] to publish and subscribe messages via the MQTT protocol. It is similar to the amqp node-type.

Prerequisites

This node-type requires mosquitto (>= 1.4.15).

Implementation

The source code of the node-type is available here: https://github.com/VILLASframework/node/blob/master/lib/nodes/mqtt.cpp

Configuration

	Format Object (object) or Format Name (string) (format_spec)
	object (Input configuration (received by VILLASnode))
	object (Output configuration (sent out by VILLASnode))
username	string The username which is used for authentication with the MQTT broker.
password	string The username which is used for authentication with the MQTT broker.
host required	string The hostname of the MQTT broker.
port	integer Default: 1883 The port number of the MQTT broker.
retain	boolean Default: false Set to true to make the will a retained message.
keepalive	integer Default: 5 The MQTT keepalive value.
qos	integer Default: 0 The quality of service (QoS) to use for the subscription.
	object
vectorize	integer Default: 1 This setting allows to send multiple samples in a single message to the destination nodes. The value of this setting determines how many samples will be combined into one packet.
	Array of Hook Object (object) or Hook Name (string) (hook_list)
builtin	boolean (Builtin hook functions) Default: true By default, each node and paths has a couple of default hooks attached to them. With this setting the attachment of built-in hooks can be disabled.

{

• "format": "villas.human",
• "in": {

  • "subscribe": "string",
  • "signals": [

    • {

      • "name": "tap_position",
      • "type": "integer",
      • "init": 0

      },
    • {

      • "name": "voltage",
      • "type": "float",
      • "unit": "V",
      • "init": 230

      }

    ],
  • "vectorize": 1,
  • "hooks": [

    • "print",
    • {

      • "type": "limit_rate",
      • "rate": 1000

      }

    ]

  },
• "out": {

  • "publish": "string",
  • "vectorize": 0,
  • "hooks": [

    • "print",
    • {

      • "type": "limit_rate",
      • "rate": 1000

      }

    ]

  },
• "username": "string",
• "password": "string",
• "host": "example.com",
• "port": 1883,
• "retain": false,
• "keepalive": 5,
• "qos": 0,
• "ssl": {

  • "enabled": true,
  • "insecure": true,
  • "cafile": "string",
  • "capath": "string",
  • "certfile": "string",
  • "keyfile": "string",
  • "cipher": "string",
  • "verify": true,
  • "tls_version": "tlsv1"

  },
• "vectorize": 1,
• "hooks": [

  • "print",
  • {

    • "type": "limit_rate",
    • "rate": 1000

    }

  ],
• "builtin": true

}

Example

node/etc/examples/nodes/mqtt.conf

nodes = {
    mqtt_node = {
        type = "mqtt"

        format = "protobuf"

        username = "guest"
        password = "guest"
        host = "localhost"
        port = 1883

        # Send ping every 5 seconds to keep connection alive
        keepalive = 5
        retain = false
        qos = 0

        out = {
            publish = "test-topic"
        }

        in = {
            subscribe = "test-topic"
        }

        ssl = {
            enabled = false
            insecure = true
            cafile = "/etc/ssl/certs/ca-bundle.crt"
            certfile = "/etc/ssl/certs/my.crt"
            keyfile = "/etc/ssl/keys/my.key"
        }
    }
}