The crononome Connector

The crononome connector generates a periodic flow of events at a configured periodicity based on the modern Gregorian calendar system.

As the name suggests - the connector is configured using cron like schedules and a user configurable data event provider by authors with the business event which can be used to trigger downstream processing.

The connector is particularly useful when using transient or persistent state via the kv connector or via the state mechanism to evict and remove stale data that is no longer current or relevant to the running system.

The connector is also useful for driving periodic events when used in concert with other connectors or pipelines to periodically poll to retrieve meta data updates to merge with in-memory state in the current solution.

Configuration

One or many cron like specifications for the event schedule and a user defined data payload.

config.troy

define connector crononome from crononome
with
  config = {
    "entries": [{
      "name": "test",                # A symbolic name for this schedule
      "expr": "* * * * * *",         # A cron schedule
      "payload": {"snot": "badger"}  # A user configurable payload value
    }]
  }
end;

Illustrative example

A simple tremor application that issues a single crononome event and uses it to trigger an exit of the tremor runtime - a common quiescence pattern in our tests driven by the crononome in this illustration.

A high level summary of this flow's logic:

graph LR A{Metronome} -->|every second| B(triggered events) B -->|passthrough| C{Standard Output} B -->|stop server| D{Exit Runtime}

The application source for this example:

define flow main
flow
  use tremor::connectors;
  use integration;
  define connector crononome from crononome
  with
    config = {
      "entries": [{
        "name": "test",
        "expr": "* * * * * *",
        "payload": {"snot": "badger"}
      }]
    }
  end;

  define pipeline main
  pipeline 
    select event.trigger from in into out;
  end;

  define pipeline exit
  pipeline 
    select {
      "exit": 0,
      "delay": 1
    } from in into out;
  end;

  create connector file from integration::write_file;
  create connector crononome;
  create connector exit from connectors::exit;
  create pipeline main;
  create pipeline exit;

  connect /connector/crononome to /pipeline/main;
  connect /connector/crononome to /pipeline/exit;
  connect /pipeline/main to /connector/file;
  connect /pipeline/exit to /connector/exit;
end;
deploy flow main;

Exercises

To further explore the crononome:

• Modify the application to stop after N events by introducing a counter
• Modify the application to trigger a HTTP GET request and serialize the response to a log file
• Replace the crononome with a crononome for periodic scheduled calendar driven events