Showing Webcal Calendar Events in Grafana

I'm running a Grafana at home, with a dashboard giving me an overview over my day. It contains information like public transport departures or the guest WiFi's password. But the most important part is a list of my upcoming appointments. Now, iCalendar files served via HTTP is not something Grafana understands out of the box. To work around this, I wrote a small service that scrapes the calendar endpoints and exposes the events as metrics in a Prometheus-compatible API.

How it works

Consider the following iCalendar file, served at an HTTP endpoint:

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//ACME//NONSGML Rocket Powered Anvil//EN
BEGIN:VEVENT
UID:20190603T032500CEST-foo
SUMMARY:Foo
DESCRIPTION:An example event
DTSTART;TZID=Europe/Zurich;VALUE=DATE-TIME:20190603T032500
DTEND;TZID=Europe/Zurich;VALUE=DATE-TIME:20190603T040000
END:VEVENT
BEGIN:VEVENT
UID:20190603T032500CEST-bar
SUMMARY:Bar
DESCRIPTION:Another example event
DTSTART;TZID=Europe/Zurich;VALUE=DATE-TIME:20190603T032500
DTEND;TZID=Europe/Zurich;VALUE=DATE-TIME:20190603T040000
END:VEVENT
END:VCALENDAR

The service retrieves this calendar from the endpoint, parses it and extracts a list of events together with metadata from it. It then serves the data in a Prometheus-compatible time series API. Clients can request all upcoming events using the following call:

GET /api/v1/query?query=events

To which the service returns the time series of events:

{
  "status": "success",
  "data": {
    "resultType": "vector",
    "result": [
      {
        "metric": {
          "__name__": "event",
          "calendar": "0",
          "uid": "20190603T032500CEST-foo",
          "summary": "Foo",
          "description": "An example event"
        },
        "value": [
          1560043497,
          1
        ]
      },
      {
        "metric": {
          "__name__": "event",
          "calendar": "1",
          "uid": "20190603T032500CEST-bar",
          "summary": "Bar",
          "description": "Another example event"
        },
        "value": [
          1560043497,
          1
        ]
      }
    ]
  }
}

Caveats

Since a Prometheus label can't be used multiple times, event categories can't be easily mapped to them. Thus, event categories are currently not exported. If someone has an idea how to model categories in the output, while keeping it easy to query and manage, feel free to contact me.

Grafana uses a hardcoded 1+1 query to test Prometheus data sources, so the API currently has a special check for that and returns 2, as expected by Grafana.

Interested?

The project, which I named iCalendar Timeseries Server, can be found on Gitlab. Each release comes with Python Wheel and Debian packages.