Use cron triggers to develop time-aware applications

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Cloudflare Workflows provide a powerful way to manage asynchronous, durable processes. The ability to explicitly schedule tasks using cron triggers and pause execution with step.sleep allows developers to build sophisticated, time-aware applications.

Chapters

• 
  Intro 0s
• 
  Interaction code 1m53s
• 
  Leaderboard code 3m21s
• 
  Wrangler.toml 3m41s
• 
  Puntificator: Using AI to develop more puns automatically 4m46s
• 
  Nested Workflows 5m55s
• 
  Npx wrangler workflow instances 6m37s
• 
  Conclusion 7m41s

Related content

If you want to dive into detail, refer to the following pages:

• Source code for the Punderful repository ↗
• Cloudflare Workflows
• Cloudflare Workers AI

Step-by-step tutorial

Workflows allow you to kick off asynchronous processes without blocking the user. This is demonstrated in the addInteraction function, which creates a new instance of the INTERACTION workflow.

Locate the addInteraction function in src/index.tsx:

See here ↗

This function is called when a user interacts with a pun (for example, likes it). Instead of performing the interaction logic directly, it offloads the work to a workflow.

Examine the InteractionWorkflow definition in src/workflows/interaction.ts. This workflow performs tasks like checking if the user/session exists and recording the interaction in the database.

See here ↗

Leaderboard Code

A common use case for background processes is crunching data and caching results, such as building a leaderboard.

Examine the LeaderboardWorkflow in src/workflows/leaderboard.ts. This workflow performs a database query to find trending puns and then stores the results in Cloudflare KV (Key-Value Store).

See here ↗

This workflow can be scheduled to run periodically to update the leaderboard data.

Wrangler.toml Configuration

The wrangler.toml file is used to configure your Worker and Workflows. This includes defining bindings to resources like KV namespaces and setting up triggers for workflows.

Open wrangler.toml and find the [triggers] section.

See here ↗

The crons array allows you to define scheduled triggers for your main Worker. The example shows a cron job configured to run every 30 minutes.

Locate the scheduled handler in your main Worker code (src/index.tsx). This handler is executed when a cron trigger fires.

See here ↗

This handler creates an instance of the LEADERBOARD_WORKFLOW, initiating the leaderboard update process on a schedule.

Puntificator: Using AI to Develop More Puns Automatically

Workflows can also be used for more complex, multi-step processes, including interacting with AI models. The PuntificatorWorkflow is an example that leverages AI to generate and evaluate new puns.

Examine the PuntificatorWorkflow definition in src/workflows/puntificator.ts.

See here ↗

This workflow includes steps to:

1. Retrieve trending puns.
2. Create a new pun based on trends using an AI model.
3. Judge the quality of the created pun using another AI model.
4. Save the pun if it meets a certain rating threshold.

Crucially, this workflow includes a step.sleep call:

See here ↗

This step pauses the workflow execution for a specified duration. This is useful for waiting to consider user feedback on a published pun before potentially taking further action based on its popularity.

Nested Workflows

Workflows can initiate other workflows, allowing you to compose complex processes from smaller, modular units.

In the PuntificatorWorkflow, find where it calls the PUBLISH workflow.

See here ↗

This demonstrates how one workflow can trigger another, enabling the separation of concerns and modular design.

Examine the PublishWorkflow in src/workflows/publish.ts.

See here ↗

This workflow handles the logic for publishing a pun, likely involving saving it to the database and making it visible on the site.

Workflow Instances

You can trigger workflows manually and inspect their execution status and output using the wrangler command-line tool.

To trigger the PuntificatorWorkflow manually:

npx wrangler workflows trigger puntificator

This command will queue an instance of the workflow. You will receive a success message and the instance ID.

To describe the latest instance of a workflow:

npx wrangler workflows instances describe puntificator latest

This command will show details about the most recent run of the specified workflow, including its start time, end time, duration, state, and the state of each individual step within the workflow. You can observe steps like create-new-pun-based-on-trends, judge-pun, save-pun, publish, and wait-for-publish (which shows a 'Sleeping' state).

Series overview

Watch Episode 1: Understand Cloudflare Workflows In this episode, we introduce Cloudflare Workflows, which provides durable execution capabilities, allowing developers to create reliable, repeatable workflows that run in the background.

Watch Episode 2: Monitor and batch your website data In this episode, we describe how Workflows can be used to process batches of data, ensuring each item in the batch goes through a defined process with reliable execution.

Watch Episode 3: Use cron triggers to develop time-aware applications In this episode, we review Workflows ability to explicitly schedule tasks using cron triggers and pause execution with `step.sleep` allows developers to build sophisticated, time-aware applications.