Experimental Cron trigger for Spin

Install from release

spin plugins install --url https://github.com/fermyon/spin-trigger-cron/releases/download/canary/trigger-cron.json

Build From source

You will need Rust and the pluginify plugin (spin plugins install --url https://github.com/itowlson/spin-pluginify/releases/download/canary/pluginify.json).

cargo build --release
spin pluginify --install

Test

You will need to build and run the spin components. Change the cron expression if needed.

cd guest
spin build --up

Installing the template

You can install the template using the following command:

spin templates install --git https://github.com/fermyon/spin-trigger-cron

Once the template is installed, you can create a new application using:

spin new -t cron-rust hello_cron --accept-defaults

To run the newly created app:

cd hello_cron
spin build --up

Trigger Configuration

The trigger type is cron, and there are no application-level configuration options.

The following options are available to set in the [[trigger.cron]] section:

Name	Type	Required?	Description
component	string or table	required	The component to run on the schedule given in cron_expression. (This is the standard Spin trigger component field.)
cron_expression	string	required	The cron expression describes the schedule for executing the component.

Cron Expression Fields

The cron_expression fields are as follows:

#  ┌──────────── sec (0–59)
#  |  ┌───────────── min (0–59)
#  |  │  ┌───────────── hour (0–23)
#  |  │  │  ┌───────────── day of month (1–31)
#  |  │  │  │  ┌───────────── month (1–12)
#  |  │  │  │  │  ┌───────────── day of week (0–6)
#  |  │  │  │  │  |  ┌─────────────- year
#  |  │  │  │  │  |  │
#  |  │  │  │  │  |  │
   *  *  *  *  *  *  * 

Cron Expression Characters

The * indicates that every value applies. For example, if sec is set to *, then every second will trigger execution. The / indicates increments. For example, if sec is set to 0/15, then starting at 0, the trigger will be executed every 15 seconds. The , indicates a list of values. For example, if sec is set to 2,8, then the trigger will execute only on the 2nd and 8th seconds of every minute. The - indicates range. For example, if the sec is set to 5-10, then the trigger will execute only on the 5th, 6th, 7th, 8th, 9th, and 10th seconds of each minute. The 0 indicates no execution. If the sec is set to 0, then the trigger can only execute on higher field values such as min, hour, etc. The lowest second increment is 60 (one minute).

Here is one example that combines a few of the fields mentioned above:

sec   min   hour   day of month   month   day of week   year
0     1/2   11,12  5-10           *       *             *

The above schedule of 0 1/2 11,12 5-10 * * * will execute on the first minute and every subsequent 2 minutes during the 11th hour and the 12 hour (noon) on days 5 through 10 of every month (regardless of the day of the week) and this will repeat through every year.

Building Cron Components

Currently only a Rust SDK is supported for guest components. The spin-cron-sdk along with the spin_sdk crate can be used to build cron components. The guest code must have a function decorated with the #[cron_component] macro. See guest/src/lib.rs for an example in rust.

The signature of the function must be fn handle_cron_event(metadata: Metadata) -> Result<(), Error>.

The Metadata object contains a single field timestamp which contains the duration since 00:00:00 UTC on 1 January 1970 (the Unix epoch) in seconds.