Connecting Telegraf to Mosquitto with output to InfluxDb

For a small project (a microcontroller with a temperature sensor) I needed a mqtt broker to process the sensors data to display it in Grafana. There’s already a TIG stack running on my server, so it was obvious to me that I will go with Mosquitto.

For some reason Mosquitto never returned any data scraped by Telegraf. At this point I was really puzzled, as all tutorials I have found online had the same configuration and a similar setup as my stack. It took me quite some time to discover that Mosquitto introduced a breaking change in version 2, as it now connects by default only to the loopback interface, which explains the issue I saw: no connections from outside of the container are successful. All tutorials I have seen on the internet are from before version 2, so there was no mention of this newly introduced behaviour.

To change this behavior a single line needs to be added to the mosquitto.conf: listener 1883 (or whatever port you’re using). After this change a connection from Telegraf is successful.

My entire mosquitto.conf looks like this after this change:

persistence true
persistence_location /mosquitto/data/
log_dest file /mosquitto/log/mosquitto.log
listener 1883
allow_anonymous true

This configuration file is mounted into the container by using a volume mount in a docker-compose file:

 mosquitto:
    image: eclipse-mosquitto:2.0.7
    container_name: mosquitto
    ports:
      - 9001:9001
      - 1883:1883
    volumes:
      - /media/enc/docker-volumes/mosquitto/conf/mosquitto.conf:/mosquitto/config/mosquitto.conf
      - /media/enc/docker-volumes/mosquitto/data/:/mosquitto/data/
      - /media/enc/docker-volumes/mosquitto/log/:/mosquitto/log/

Telegraf is configured to subscribe to the mqtt topics by using the mqtt_consumer of inputs and outputting the data to influxdb:

[[outputs.influxdb]]
  urls = ["http://influxdb:8086"]
  database = "sensors"
  skip_database_creation = true

[[inputs.mqtt_consumer]]
  servers = ["tcp://mosquitto:1883"]
  topics = [
    "bedroom/#"
  ]

After this simple change Mosquitto accepts external (outside of the container) connections and the Telegraf is able to subscribe to the data and send it to InfluxDb.