This exporter translates from MQTT topics to prometheus metrics. The core design is that clients send arbitrary JSON messages on the topics. The translation between the MQTT representation and prometheus metrics is configured in the mqtt2prometheus exporter since we often can not change the IoT devices sending the messages. Clients can push metrics via MQTT to an MQTT Broker. This exporter subscribes to the broker and expose the received messages as prometheus metrics. Currently, the exporter supports only MQTT 3.1.

I wrote this exporter to expose metrics from small embedded sensors based on the NodeMCU to prometheus. The used arduino scetch can be found in the dht22tomqtt repository. A local hacking environment with mqtt2prometheus, a MQTT broker and a prometheus server is in the hack directory.

This exporter makes some assumptions about the MQTT topics. This exporter assumes that each client publish the metrics into a dedicated topic. The regular expression in the configuration field mqtt.device_id_regex defines how to extract the device ID from the MQTT topic. This allows an arbitrary place of the device ID in the mqtt topic. For example the tasmota firmware pushes the telemetry data to the topics tele/<deviceid>/SENSOR.

Let us assume the default configuration from configuration file. A sensor publishes the following message

{"temperature":23.20,"humidity":51.60, "computed": {"heat_index":22.92} }

to the MQTT topic devices/home/livingroom. This message becomes the following prometheus metrics:

temperature{sensor="livingroom",topic="devices/home/livingroom"} 23.2
heat_index{sensor="livingroom",topic="devices/home/livingroom"} 22.92
humidity{sensor="livingroom",topic="devices/home/livingroom"} 51.6

The label sensor is extracted with the default device_id_regex (.*/)?(?P<deviceid>.*) from the MQTT topic devices/home/livingroom. The device_id_regex is able to extract exactly one label from the topic path. It extracts only the deviceid regex capture group into the sensor prometheus label. To extract more labels from the topic path, have a look at this FAQ answer.

The topic path can contain multiple wildcards. MQTT has two wildcards:

• +: Single level of hierarchy in the topic path
• #: Many levels of hierarchy in the topic path

This page explains the wildcard in depth.

For example the topic_path: devices/+/sensors/# will match:

• devices/home/sensors/foo/bar
• devices/workshop/sensors/temperature

The exporter interprets mqtt_name as gojsonq paths. Those paths will be used to find the value in the JSON message. For example mqtt_name: computed.heat_index addresses

{
  "computed": {
    "heat_index":22.92
  }
}

Some sensors might use a . in the JSON keys. Therefore, there the configuration option json_parsing.seperator in the exporter config. This allows us to use any other string to separate hierarchies in the gojsonq path. E.g let's assume the following MQTT JSON message:

{
  "computed": {
    "heat.index":22.92
  }
}

We can now set json_parsing.seperator to /. This allows us to specify mqtt_name as computed/heat.index. Keep in mind, json_parsing.seperator is a global setting. This affects all mqtt_name fields in your configuration.

An example configuration for the tasmota based Gosund SP111 device is given in examples/gosund_sp111.yaml.

To build the exporter run:

make build

Only the latest two Go major versions are tested and supported.

To start the public available image run:

docker run -it -v "$(pwd)/config.yaml:/config.yaml"  -p  9641:9641 ghcr.io/hikhvar/mqtt2prometheus:latest 

Please have a look at the latest relase to get a stable image tag. The latest tag may break at any moment in time since latest is pushed into the registries on every git commit in the master branch.

To build a docker container with the mqtt2prometheus exporter included run:

make container

To run the container with a given config file:

docker run -it -v "$(pwd)/config.yaml:/config.yaml"  -p 9641:9641 mqtt2prometheus:latest 

The exporter can be configured via command line and config file.

Available command line flags:

Usage of ./mqtt2prometheus:
  -config string
        config file (default "config.yaml")
  -listen-address string
        listen address for HTTP server used to expose metrics (default "0.0.0.0")
  -listen-port string
        HTTP port used to expose metrics (default "9641")
  -log-format string
        set the desired log output format. Valid values are 'console' and 'json' (default "console")
  -log-level value
        sets the default loglevel (default: "info")
  -version
        show the builds version, date and commit
  -web-config-file string
        [EXPERIMENTAL] Path to configuration file that can enable TLS or authentication for metric scraping.

The logging is implemented via zap. The logs are printed to stderr and valid log levels are those supported by zap.

The config file can look like this:

mqtt:
 # The MQTT broker to connect to
 server: tcp:https://127.0.0.1:1883
 # Optional: Username and Password for authenticating with the MQTT Server
 user: bob
 password: happylittleclouds
 # Optional: for TLS client certificates
 ca_cert: certs/AmazonRootCA1.pem
 client_cert: certs/xxxxx-certificate.pem.crt
 client_key: certs/xxxxx-private.pem.key
 # Optional: Used to specify ClientID. The default is <hostname>-<pid>
 client_id: somedevice
 # The Topic path to subscribe to. Be aware that you have to specify the wildcard, if you want to follow topics for multiple sensors.
 topic_path: v1/devices/me/+
 # Optional: Regular expression to extract the device ID from the topic path. The default regular expression, assumes
 # that the last "element" of the topic_path is the device id.
 # The regular expression must contain a named capture group with the name deviceid
 # For example the expression for tasamota based sensors is "tele/(?P<deviceid>.*)/.*"
 device_id_regex: "(.*/)?(?P<deviceid>.*)"
 # The MQTT QoS level
 qos: 0
cache:
 # Timeout. Each received metric will be presented for this time if no update is send via MQTT.
 # Set the timeout to -1 to disable the deletion of metrics from the cache. The exporter presents the ingest timestamp
 # to prometheus.
 timeout: 24h
json_parsing:
 # Separator. Used to split path to elements when accessing json fields.
 # You can access json fields with dots in it. F.E. {"key.name": {"nested": "value"}}
 # Just set separator to -> and use key.name->nested as mqtt_name
 separator: .
# This is a list of valid metrics. Only metrics listed here will be exported
metrics:
 # The name of the metric in prometheus
 - prom_name: temperature
  # The name of the metric in a MQTT JSON message
   mqtt_name: temperature
  # The prometheus help text for this metric
   help: DHT22 temperature reading
  # The prometheus type for this metric. Valid values are: "gauge" and "counter"
   type: gauge
  # A map of string to string for constant labels. This labels will be attached to every prometheus metric
   const_labels:
    sensor_type: dht22
  # The name of the metric in prometheus
 - prom_name: humidity
  # The name of the metric in a MQTT JSON message
   mqtt_name: humidity
  # The prometheus help text for this metric
   help: DHT22 humidity reading
  # The prometheus type for this metric. Valid values are: "gauge" and "counter"
   type: gauge
  # A map of string to string for constant labels. This labels will be attached to every prometheus metric
   const_labels:
    sensor_type: dht22
  # The name of the metric in prometheus
 - prom_name: heat_index
  # The path of the metric in a MQTT JSON message
   mqtt_name: computed.heat_index
  # The prometheus help text for this metric
   help: DHT22 heatIndex calculation
  # The prometheus type for this metric. Valid values are: "gauge" and "counter"
   type: gauge
  # A map of string to string for constant labels. This labels will be attached to every prometheus metric
   const_labels:
    sensor_type: dht22
  # The name of the metric in prometheus
 - prom_name: state
  # The name of the metric in a MQTT JSON message
   mqtt_name: state
  # Regular expression to only match sensors with the given name pattern
   sensor_name_filter: "^.*-light$"
  # The prometheus help text for this metric
   help: Light state
  # The prometheus type for this metric. Valid values are: "gauge" and "counter"
   type: gauge
  # A map of string to string for constant labels. This labels will be attached to every prometheus metric
   const_labels:
    sensor_type: ikea
  # When specified, enables mapping between string values to metric values.
   string_value_mapping:
    # A map of string to metric value.
    map:
     off: 0
     low: 0
    # Metric value to use if a match cannot be found in the map above.
    # If not specified, parsing error will occur.
    error_value: 1
  

Having the MQTT login details in the config file runs the risk of publishing them to a version control system. To avoid this, you can supply these parameters via environment variables. MQTT2Prometheus will look for MQTT2PROM_MQTT_USER and MQTT2PROM_MQTT_PASSWORD in the local environment and load them on startup.

Create a file to store your login details, for example at ~/secrets/mqtt2prom:

#!/bin/bash
export MQTT2PROM_MQTT_USER="myUser" 
export MQTT2PROM_MQTT_PASSWORD="superpassword"

Then load that file into the environment before starting the container:

 source ~/secrets/mqtt2prom && \
  docker run -it \
  -e MQTT2PROM_MQTT_USER \
  -e MQTT2PROM_MQTT_PASSWORD \
  -v "$(pwd)/examples/config.yaml:/config.yaml" \
  -p 9641:9641 \
  ghcr.io/hikhvar/mqtt2prometheus:latest

The exporter can only listen to one topic_path per instance. If you have to listen to two different topic_paths it is recommended to run two instances of the mqtt2prometheus exporter. You can run both on the same host or if you run in Kubernetes, even in the same pod.

A regular use case is, that user want to extract more labels from the topic path. E.g. they have sensors not only in their home but also in their workshop and they encode the location in the topic path. E.g. a sensor pushes the message

{"temperature":3.0,"humidity":34.60, "computed": {"heat_index":15.92} }

to the topic devices/workshop/storage, this will produce the prometheus metrics with the default configuration.

temperature{sensor="storage",topic="devices/workshop/storage"} 3.0
heat_index{sensor="storage",topic="devices/workshop/storage"} 15.92
humidity{sensor="storage",topic="devices/workshop/storage"} 34.60

The following prometheus relabel_config will extract the location from the topic path as well and attaches the location label.

relabel_config:
  - source_labels: [ "topic" ]
    target_label: location
    regex: '/devices/(.*)/.*'
    action: replace
    replacement: "$1"

With this config added to your prometheus scrape config you will get the following metrics in prometheus storage:

temperature{sensor="storage", location="workshop", topic="devices/workshop/storage"} 3.0
heat_index{sensor="storage", location="workshop", topic="devices/workshop/storage"} 15.92
humidity{sensor="storage", location="workshop", topic="devices/workshop/storage"} 34.60