mqtt2prom

This service is a mqtt-to-prometheus gateway.

it is configured with the following ENV-Variables, the ones suffiexed with a * are mandatory, default values are after |:

MQTT_HOST*
MQTT_PORT|1883
MQTT_USER
MQTT_PASS
MQTT_CLIENT_ID|mqtt2prometheus
MQTT_TOPIC|prometheus
MQTT_QOS|2
IGNORE_RETAINED|1

IGNORE_RETAINED: when set, retained messages are dropped and will be reported as errors.

it will listen on the configured mqtt server at $MQTT_TOPIC for metrics in json_format.

The payload needs to be an object containing only the following keys:

• name (string): the name of the metric
• value (number): the value of the metric
• labels (object, optional): an object containing the labels for the metric (key-value pairs of strings)

According to prometheus conventions, the metric name and the label names need to be a lower or upper case letter or a underscore followed by all case leters, numbers or underscores.

These are all valid payloads:

{
  "name": "temperature",
  "value": 30.7,
  "labels": {
    "unit": "°C",
    "location": "Werkstatt"
  }
}

{
  "name": "temperature",
  "value": 30.7,
  "labels": {}
}

{
  "name": "temperature",
  "value": 30.7
}

The service will expose the metrics on the /metrics endpoint. All metrics will be presented for about 5 minutes, and exported with their eventtime as a timestamp.

Metric types are not currently implemented, all metrics are exported without a type. This might change when prometheus supports it.

The service will report errors in received messages to STDERR and to $MQTT_TOPIC/error. Possible errors are:

• invalid json
• missing name or value key
• invalid name (prometheus conventions)
• invalid value (not a number)
• invalid labels (not an object)
• invalid label names (not a sting or not a valid prometheus label name)
• invalid label values (not a string)
• additional information in the payload (not one of name, value, labels)

The error message describes the error type and repeats the payload that caused the error.

There is a comment block on top if the metric that shows some metadata for human consumption.

mem usage and mem usage peak is according to memory_get_usage() and memory_get_peak_usage() respectively. in both cases it gives 2 values, the first is the acutally used value, the second is tha allocated.

A new export is written either

• once oper second if new events are incoming.
• every 15 seconds if no new events are incoming, to update stats and remove stale entries.

There is a 60 second period on startup where metrics are received but not exported, in case the service crashes and there are previous exported metrics that are not polled by prometheus yet.