# MQTT2Prometheus
This exporter is an analog to the [Prometheus Pushgateway](https://github.com/prometheus/pushgateway). Clients can push 
metrics via MQTT to an MQTT Broker. This exporter subscribes to the broker and
publish the received messages as prometheus metrics. I wrote this exporter to publish
metrics from small embedded sensors based on the NodeMCU to prometheus. The used arduino scetch can be found in the [dht22tomqtt](https://github.com/hikhvar/dht22tomqtt) repository.

## Assumptions about Messages and Topics
This exporter makes some assumptions about the message format and MQTT topics. This exporter assumes that each
client publish the metrics into a dedicated topic. The last level topic becomes the `sensor` label in prometheus.
This exporter assume that the message are JSON objects with only float fields. The golang type for the messages is: 

```go
type MQTTPayload map[string]float64
```

For example the message

```json
{"temperature":23.20,"humidity":51.60,"heat_index":22.92}
```

published to the MQTT topic `devices/me/livingroom` becomes the following prometheus metrics:

```text
temperature{sensor="livingroom"} 23.2
heat_index{sensor="livingroom"} 22.92
humidity{sensor="livingroom"} 51.6
```

## Build

To build the exporter run:

```bash
make build
```

### Docker

#### Use Public Image

To start the public available image run:
```bash
docker run -it -v "$(pwd)/config.yaml:/config.yaml"  -p 8002:8002 hikhvar/mqtt2prometheus:latest 
```

#### Build The Image locally
To build a docker container with the mqtt2prometheus exporter included run:

```bash
make container
```

To run the container with a given config file:

```bash
docker run -it -v "$(pwd)/config.yaml:/config.yaml"  -p 8002:8002 mqtt2prometheus:latest 
```

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

### Commandline
Available command line flags:

```text
Usage of ./mqtt2prometheus.linux_amd64:
  -config string
        config file (default "config.yaml")
  -listen-address string
        listen address for HTTP server used to expose metrics
  -listen-port string
        HTTP port used to expose metrics (default "8002")

```

### Config file
The config file can look like this:

```yaml
# Settings for the MQTT Client. Currently only these three are supported
mqtt:
  # The MQTT broker to connect to
  server: tcp://127.0.0.1:1883
  # The Topic path to subscripe to. Actually this will become `$topic_path/+`
  topic_path: v1/devices/me
  # The MQTT QoS level
  qos: 0
cache:
  # Timeout. Each received metric will be presented for this time if no update is send via MQTT
  timeout: 2min
# 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 name of the metric in a MQTT JSON message
    mqtt_name: 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%       
```