Triggering Dispatch pipelines using Cron expressions

Prerequisites

This tutorial assumes that you have done the following:

• Installed Dispatch
• Set up a Repository in Dispatch
• Checked out the “hello-world” repository
• Configured the “hello-world” application for Dispatch CI (via dispatch ci repository create)

Introduction

In this tutorial, you will learn how to configure a periodically triggered task by configuring and using a cron expression.

Configure Cron Trigger in Dispatchfile

Periodic pipelines enable a Dispatch pipeline to be executed at a predetermined time according to a schedule. This schedule can be set to execute a set of Dispatch tasks as defined within the Dispatchfile. For example, a development team may choose to create a schedule that executes the pipeline everyday at midnight to represent their daily build. Dispatch leverages the common cron model for scheduling these pipeline runs. To schedule a pipeline, and trigger it to be executed, a cron action must be specified for the action. Each cron action needs to be named uniquely (within the scope of a single Dispatchfile) using the name field. The cron condition accepts a mandatory field schedule and an optional field revision. The schedule field is backed by the Kubernetes CronJob Schedule field. The revision field corresponds to the actual revision of the scm repository to pull in to run the tests. This can point to a branch/tag/commit sha. If not specified, this defaults to the default branch of scm repository. This is how a simple action should look:

{
  "name": "unique-name-of-action",
  "tasks": ["list", "of", "tasks"],
  "on" : {
    "cron": {
      "schedule": "standard-cron-syntax-schedule",
      "revision": "optional-revision"
    }
  }
}

As a real world example, take a look at a task written in Cue from the pipeline configuration docs

#!mesosphere/dispatch-cue:v0.4

resource "src-git": {
  type: "git"
  param url: "$(context.git.url)"
  param revision: "$(context.git.commit)"
}

task "test": {
  inputs: ["src-git"]

  steps: [
    {
      name: "test"
      image: "golang:1.15.7-buster"
      command: [ "go", "test", "./..." ]
      workingDir: "/workspace/src-git"
    }
  ]
}

actions: [
  {
    name: "my-nightly-build"
    tasks: ["test"]
    on: cron: schedule: "@daily"
  }
]

The action named my-nightly-build runs the task named test every day at midnight. For more information, see the configuration reference.