Strudel

Export DHT22 temperature and humidity sensor readings as Prometheus metrics.

Features

Strudel reads temperature and humidity information from a DHT22 sensor and exports the values as Prometheus metrics. It is best run on a Raspberry PI (3 or 4).

The following metrics are exported:

• strudel_temperature_degrees - Degrees celsius measured by the sensor.
• strudel_relative_humidity - Relative humidity (from 0 to 100) measured by the sensor.
• strudel_last_read_timestamp - UNIX timestamp of the last time the sensor was correctly read.
• strudel_collections_total - Total number of attempts to read the sensor.
• strudel_errors_total - Total errors by type while trying to read the sensor.
• strudel_read_timing_seconds - Time taken to read the sensor, in seconds.

Build

strudel is a Rust program and must be built from source using a Rust toolchain . Since it's meant to be run on a Raspberry PI, you will also likely need to cross-compile it. If you are on Ubuntu GNU/Linux, you'll need the following packages installed for this.

apt-get install gcc-arm-linux-gnueabihf musl-tools

This will allow you to build for ARMv7 platforms and build completely static binaries (respectively).

Next, make sure you have a Rust toolchain for ARMv7, assuming you are using the rustup tool.

rustup target add armv7-unknown-linux-musleabihf

Next, you'll need to build strudel itself for ARMv7.

cargo build --release --target armv7-unknown-linux-musleabihf

Install

GPIO Pin

In order to read the DHT22 sensor, it must be connected to one of the General Purpose IO pins (GPIO) on your Raspberry PI (duh). The included Systemd unit file assumes that you have picked GPIO pin 17 for the data line of the sensor. If this is not the case, you'll have to modify the unit file. For a list of available pins, see the Raspberry PI documentation.

Run

In order to read and write the device /dev/gpiomem, strudel must run as root. You can run strudel as a Systemd service using the provided unit file. This unit file assumes that you have copied the resulting strudel binary to /usr/local/bin/strudel.

sudo cp target/armv7-unknown-linux-musleabihf/release/strudel /usr/local/bin/strudel
sudo cp ext/strudel.service /etc/systemd/system/strudel.service
sudo systemctl daemon-reload
sudo systemctl enable strudel.service
sudo systemctl start strudel.serivce

Prometheus

Prometheus metrics are exposed on port 9781 at /metrics. Once strudel is running, configure scrapes of it by your Prometheus server. Add the host running strudel as a target under the Prometheus scrape_configs section as described by the example below.

NOTE: The DHT22 sensor can only be read every two seconds, at most. By default, the sensor is read every 30s, in the background (not in response to Prometheus scrapes). Thus, scrapes by Prometheus more frequent than 30s don't have any benefit unless the refresh interval for strudel is adjusted as well.

# Sample config for Prometheus.

global:
  scrape_interval:     1m
  evaluation_interval: 1m
  external_labels:
      monitor: 'my_prom'

scrape_configs:
  - job_name: strudel
    static_configs:
      - targets: ['example:9781']

References

Some helpful documentation, articles, etc. used to create Strudel

• Datasheet
• DHT11 Driver in Rust
• RPPal crate

License

Strudel is available under the terms of the GPL, version 3.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you shall be licensed as above, without any additional terms or conditions.