MQTT2Prometheus

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 sketch 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.

Assumptions about Messages and Topics

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

JSON Separator

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.

Some devices like Shelly Plus H&T publish one metric per-topic in a JSON format:

shellies/shellyplusht-xxx/status/humidity:0 {"id": 0,"rh":51.9}

You can use PayloadField to extract the desired value.

Tasmota

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

Build

To build the exporter run:

make build

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

Docker

Use Public Image

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.

Build The Image locally

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

Configuration

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

Commandline

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.
  -treat-mqtt-password-as-file-name bool (default: false)
        treat MQTT2PROM_MQTT_PASSWORD environment variable as a secret file path e.g. /var/run/secrets/mqtt-credential. Useful when docker secret or external credential management agents handle the secret file.

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

Config file

The config file can look like this:

mqtt:
 # The MQTT broker to connect to
 server: tcp://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
 # NOTE: Only one of metric_per_topic_config or object_per_topic_config should be specified in the configuration
 # Optional: Configures mqtt2prometheus to expect a single metric to be published as the value on an mqtt topic.
 metric_per_topic_config:
  # A regex used for extracting the metric name from the topic. Must contain a named group for `metricname`.
  metric_name_regex: "(.*/)?(?P<metricname>.*)"
 # Optional: Configures mqtt2prometheus to expect an object containing multiple metrics to be published as the value on an mqtt topic.
 # This is the default. 
 object_per_topic_config:
  # The encoding of the object, currently only json is supported
  encoding: JSON
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
 # Path to the directory to keep the state for monotonic metrics.
 state_directory: "/var/lib/mqtt2prometheus"
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 scale of the metric in a MQTT JSON message (prom_value = mqtt_value * scale)
   mqtt_value_scale: 100
  # 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$"
  # The prometheus help text for this metric
   help: Light state
  # The prometheus type for this metric. Valid values are: "gauge" and "counter"
   type: gauge
  # according to prometheus exposition format timestamp is not mandatory, we can omit it if the reporting from the sensor is sporadic
   omit_timestamp: true
  # A map of string to string for constant labels. This labels will be attached to every prometheus metric
   const_labels:
    sensor_type: ikea
  # When specified, enables mapping between string values to metric values.
   string_value_mapping:
    # A map of string to metric value.
    map:
     off: 0
     low: 0
    # Metric value to use if a match cannot be found in the map above.
    # If not specified, parsing error will occur.
    error_value: 1
  # The name of the metric in prometheus
 - prom_name: total_light_usage_seconds
  # The name of the metric in a MQTT JSON message
   mqtt_name: state
  # Regular expression to only match sensors with the given name pattern
   sensor_name_filter: "^.*-light$"
  # The prometheus help text for this metric
   help: Total time the light was on, in seconds
  # The prometheus type for this metric. Valid values are: "gauge" and "counter"
   type: counter
  # according to prometheus exposition format timestamp is not mandatory, we can omit it if the reporting from the sensor is sporadic
   omit_timestamp: true
  # 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
  # Sum up the time the light is on, see the section "Expressions" below.
  expression: "value > 0 ? last_result + elapsed.Seconds() : last_result"
  # The name of the metric in prometheus
 - prom_name: total_energy
  # The name of the metric in a MQTT JSON message
   mqtt_name: aenergy.total
  # Regular expression to only match sensors with the given name pattern
   sensor_name_filter: "^shellyplus1pm-.*$"
  # The prometheus help text for this metric
   help: Total energy used
  # The prometheus type for this metric. Valid values are: "gauge" and "counter"
   type: counter
  # This setting requires an almost monotonic counter as the source. When monotonicy is enforced, the metric value is regularly written to disk. Thus, resets in the source counter can be detected and corrected by adding an offset as if the reset did not happen. The result is a true monotonic increasing time series, like an ever growing counter.
   force_monotonicy: true

Environment Variables

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.

Example use with Docker

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

Example use with Docker secret (in swarm)

Create a docker secret to store the password(mqtt-credential in the example below), and pass the optional treat-mqtt-password-as-file-name command line argument.

  mqtt_exporter_tasmota:
    image: ghcr.io/hikhvar/mqtt2prometheus:latest 
    secrets:
      - mqtt-credential 
    environment:
      - MQTT2PROM_MQTT_USER=mqtt
      - MQTT2PROM_MQTT_PASSWORD=/var/run/secrets/mqtt-credential
    entrypoint:
      - /mqtt2prometheus
      - -log-level=debug
      - -treat-mqtt-password-as-file-name=true
    volumes:
        - config-tasmota.yml:/config.yaml:ro

Expressions

Metric values can be derived from sensor inputs using complex expressions. Set the metric config option expression to the desired formular to calculate the result from the input. Here's an example which integrates all positive values over time:

expression: "value > 0 ? last_result + value * elapsed.Seconds() : last_result"

During the evaluation, the following variables are available to the expression:

value - the current sensor value (after string-value mapping, if configured)
last_value - the value during the previous expression evaluation
last_result - the result from the previous expression evaluation
elapsed - the time that passed since the previous evaluation, as a Duration value

The language definition describes the expression syntax. In addition, the following functions are available:

now() - the current time as a Time value
int(x) - convert x to an integer value
float(x) - convert x to a floating point value
round(x) - rounds value x to the nearest integer
ceil(x) - rounds value x up to the next higher integer
floor(x) - rounds value x down to the next lower integer
abs(x) - returns the x as a positive number
min(x, y) - returns the minimum of x and y
max(x, y) - returns the maximum of x and y

Time and Duration values come with their own methods which can be used in expressions. For example, elapsed.Milliseconds() yields the number of milliseconds that passed since the last evaluation, while now().Sub(elapsed).Weekday() returns the day of the week during the previous evaluation.

The last_value, last_result, and the timestamp of the last evaluation are regularly stored on disk. When mqtt2prometheus is restarted, the data is read back for the next evaluation. This means that you can calculate stable, long-running time serious which depend on the previous result.

Evaluation Order

It is important to understand the sequence of transformations from a sensor input to the final output which is exported to Prometheus. The steps are as follows:

The sensor input is converted to a number. If a string_value_mapping is configured, it is consulted for the conversion.
If an expression is configured, it is evaluated using the converted number. The result of the evaluation replaces the converted sensor value.
If force_monotonicy is set to true, any new value that is smaller than the previous one is considered to be a counter reset. When a reset is detected, the previous value becomes the value offset which is automatically added to each consecutive value. The offset is persistet between restarts of mqtt2prometheus.
If mqtt_value_scale is set to a non-zero value, it is applied to the the value to yield the final metric value.

Frequently Asked Questions

Listen to multiple Topic Pathes

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.

Extract more Labels from the Topic Path

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

Name		Name	Last commit message	Last commit date
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.github		.github
cmd		cmd
docs		docs
examples		examples
freebsd		freebsd
fuzzing		fuzzing
hack		hack
pkg		pkg
release		release
systemd		systemd
.dockerignore		.dockerignore
.gitignore		.gitignore
.goreleaser.yml		.goreleaser.yml
Dockerfile		Dockerfile
LICENSE		LICENSE
Makefile		Makefile
Readme.md		Readme.md
config.yaml.dist		config.yaml.dist
go.mod		go.mod
go.sum		go.sum
renovate.json		renovate.json

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MQTT2Prometheus

Assumptions about Messages and Topics

JSON Separator

Tasmota

Build

Docker

Use Public Image

Build The Image locally

Configuration

Commandline

Config file

Environment Variables

Example use with Docker

Example use with Docker secret (in swarm)

Expressions

Evaluation Order

Frequently Asked Questions

Listen to multiple Topic Pathes

Extract more Labels from the Topic Path

About

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Contributors 24

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hikhvar/mqtt2prometheus

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MQTT2Prometheus

Assumptions about Messages and Topics

JSON Separator

Tasmota

Build

Docker

Use Public Image

Build The Image locally

Configuration

Commandline

Config file

Environment Variables

Example use with Docker

Example use with Docker secret (in swarm)

Expressions

Evaluation Order

Frequently Asked Questions

Listen to multiple Topic Pathes

Extract more Labels from the Topic Path

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