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MQTT Prometheus Message Exporter

It's a small service which will convert mqtt messages to prometheus metrics.

How it works:

For getting mqtt messages we need to subscribe to topics, and also to parse and convert the messages to metrics we need some "pattern" syntax.

Path generation

For any given pattern the app will figure out which topic its need to subscribe. After the subscribes it will try to parse messages as jsons. If the given result is a single number that is our "measure". If the given result is a json-object, we flatten that object. At each message we will get a list of "path" + value.

For example the topic is my/thermostat, and the json message is:

{
  "num": 10,
  "inner": {
    "num": 5,
    "arr": [1, 2, 3],
    "str": "test",
    "bool": false,
    "null": null
  },
  "so": {
    "deep": {
      "really": {
        "really": 8
      }
    }
  }
}

We will end up with these paths:

"my/thermostat/num" -> 10, 
"my/thermostat/inner/num" -> 5, 
"my/thermostat/inner/bool" -> 0, 
"my/thermostat/so/deep/really/really" -> 8

The app will parse:

• json numbers, as is
• json booleans to 0/1
• json strings to 0/1 if they follows https://yaml.org/type/bool.html (+online/offline)
• json objects (as flattened)

The app will drop:

• json null-s
• json strings which can't be converted to bools
• json arrays

Pattern to prometheus metric

The paths can be matched and converted to prometheus metrics with three operators:

• [[prefix]] will use the matching segment in the metric name
• [[prefixes]] should be only in tail position and it will use all the remaining segments in the metric name
• [[any]] will match to any segment and "drops" it
• <<label>> will create a label with the name name of label and the walue will be the path sagment

Examples for the path of my/thermostat/so/deep/really/really:

• my/[[prefix]]/so/deep/really/really will be a metric named thermostat
• my/[[prefix]]/so/[[any]]/really/[[any]] will be a metric named thermostat
• my/<<device>>/[[prefix]]/deep/really/[[prefix]] will be a metric named so_really with a label {device=thermostat}
• my/<<device>>/[[prefix]]/deep will not match and will be dropped
• my/<<device>>/[[prefix]]/deep/[[prefixes]] will be a metric named so_really_really with a label {device=thermostat}

Subscribe optimization syntax in patterns:

The app will try to optimize the subscriptions. If you add the pattern my/thermostat it will subscribe to my/#. If you have a pattern like my/<<device>>/[[segment]]/deep/[[segments]] and you only interested the topics which has three segments you can help with adding a pipe segment.

Examples:

• my/<<device>>/[[prefix]]/deep/[[prefixes]] subscribes to my/#
• my/<<device>>/[[prefix]]/|/deep/[[prefixes]] subscribes to my/+/+ (and will match like the previous one)

Other notes:

• You should add a prefix to every pattern (check the config)!
  • So a metrics will looks like iot_pressure instead of just preasure
• The special characters will be cut out from topic names or json keys (before they would appear in the prometheus output).
• The empty segments (after the special char removal) will be dropped.
• Spaces will convert to _
• Topic names and json keys will be lower-cased both in prometheus names and labels
• Patterns will match "as-is" so if you have special characters in the topic names and you want to match to them you should use those characters on topic names too!
• / in topic names, or in json keys are untested and I think it should not work.
• | is a bad topic name or json key, pls don't use it and the parser will be happy :D
• topicnames with starting << and ending >> are cursed, you can match them as a segment
• topicnames with the exact [[prefix]] and [[prefixes]] name are cursed too, they will go to the metric name as prefix and prefixes
• " character is removed from label values
• label names starting with __ could behave as not expected (they are reserved for prometheus internal according to the docs)
• non valid metric names and metric labels will be prefixed with _x_, and the non-valid characters will be replaced to _ if you see something like this try to follow the official prometheus docs with your namings
• if you have other use-case or idea pls open an issue

Config:

For example config check the example.conf!

mqtt.username/mqtt.password are not required. If you miss one of these fields the app will try to connect as an unauthenticated/guest client.

mqtt.useTls are not required. If you have a non self-signed TLS enaled endpoint switching this to true should work.

mqtt.maxPacketSize are not required. The default value is 4096.

selfMetrics is an optional block, the exporter can export it's own uptime for debugging and crash checking reasons.

For working (and non working) pattern examples check the TopicParserSpec file, under the tests (or read the upper sections to understand them)!

Docker usage example:

You need to mount up a config file, and set the CONF_PATH env var to that location.

Compose file example:

mqtt-prom-exp:
    restart: unless-stopped
    image: ghcr.io/tg44/mqtt-prometheus-message-exporter
    volumes:
      - /hdd/docker/mosquitto/config/exporter.conf:/app/exporter.conf
    ports:
      - "9324:9000"
    environment:
      - 'CONF_PATH=/app/exporter.conf'

With the config above the metrics will be available at localhost:9324/metrics.

Local testing docker run -p 9324:9000 -v ${PWD}/example.conf:/app/exporter.conf -e CONF_PATH=/app/exporter.conf ghcr.io/tg44/mqtt-prometheus-message-exporter

Breaking changes

• 2021.11.13
  • we will permanently move away from dockerhub, the latest images will be pushed, but the documentation and the other infos will only be updated here
    • DH freezes the free builds, while GH-Actions not only build free, but gives us public repositories too

Contribution

If you have any idea about the base functionality or the config/pattern syntax, just start a new issue/pr and we can talk about the use-cases, pros and cons!

Prometheus exporter implementation

I was trigger happy at the beginning and I implemented a closely complete prometheus exporter lib. If you interested in it, you should check tg44/prometheus-scala-exporter.