MQTT

The MQTT output publishes each message to an MQTT broker topic. It supports QoS 0/1/2, clean sessions, keep-alive, retained messages, and optional username/password authentication.

Configuration

Field	Type	Required	Default	Description
type	string	yes	—	Fixed value "mqtt"
host	string	yes	—	MQTT broker hostname.
port	integer	yes	—	MQTT broker port.
client_id	string	yes	—	Client identifier.
username	string	no	—	Username for authentication.
password	string	no	—	Password for authentication.
topic	object	yes	—	Destination topic (expression; see below).
qos	integer	no	—	Quality of Service: 0, 1, or 2.
clean_session	boolean	no	—	Whether to use a clean session.
keep_alive	integer	no	—	Keep-alive interval in seconds.
retain	boolean	no	—	Whether to retain the message on the broker.
value_field	string	no	—	Record field used as the message payload.

topic

topic is an Expr<String> object with one of these shapes:

Field	Type	Required	Description
type	string	yes	value (static) or expr (SQL expression).
value	string	yes (value)	Static topic name.
expr	string	yes (expr)	SQL expression evaluated per message.

Examples

Static topic

output:
  type: "mqtt"
  host: "localhost"
  port: 1883
  client_id: "my-client"
  username: "user"
  password: "pass"
  topic:
    type: "value"
    value: "my-topic"
  qos: 2
  clean_session: true
  keep_alive: 60
  retain: true
  value_field: "message"

Dynamic topic via SQL expression

output:
  type: "mqtt"
  host: "localhost"
  port: 1883
  client_id: "sensor-client"
  topic:
    type: "expr"
    expr: "concat('sensor/', id)"
  qos: 1