MSDN Documentation

Implementing Scheduled Tasks with Azure Functions

Azure Functions provide a powerful, serverless way to run code on a schedule. This allows you to automate recurring tasks, batch processing, data synchronization, and much more without managing infrastructure. This article explores how to create and manage scheduled tasks using the Timer Trigger in Azure Functions.

Understanding the Timer Trigger

The Timer Trigger in Azure Functions allows you to execute a function at a specified time. It's based on the CRON expression format, which is a standard way to define schedules.

CRON Expressions

A CRON expression consists of six fields (though some CRON implementations support seven), separated by spaces:

1. Minute (0 - 59)
2. Hour (0 - 23)
3. Day of Month (1 - 31)
4. Month (1 - 12)
5. Day of Week (0 - 6, where 0 is Sunday, or Sun, Mon, Tue, etc.)
6. Year (optional, can be specified as a 4-digit year or range)

Here are some common examples:

• 0 * * * * * - Run every minute.
• 0 0 * * * * - Run every hour at the start of the hour.
• 0 0 12 * * * - Run every day at 12:00 PM (noon).
• 0 0 8 * * MON-FRI - Run every weekday at 8:00 AM.
• 0 0 1 1 * * - Run on January 1st at midnight.

Creating a Timer Triggered Function

You can create a Timer Triggered function using the Azure portal, Azure CLI, or your preferred development tools.

Example: Using C#

When creating a new function, select the Timer Trigger template. The core of the function will look something like this:

using System;
using Microsoft.Azure.WebJobs;
using Microsoft.Extensions.Logging;

namespace AzureFunctions.ScheduledTasks
{
    public static class TimerTriggerFunction
    {
        [FunctionName("MyTimerTrigger")]
        public static void Run([TimerTrigger("0 */5 * * * *")]TimerInfo myTimer, ILogger log)
        {
            log.LogInformation($"C# Timer trigger function executed at: {DateTime.Now}");
            
            // Your scheduled task logic goes here.
            // For example, fetch data, perform maintenance, send notifications, etc.

            if (myTimer.IsPastDue)
            {
                log.LogWarning("Timer is past due!");
            }
        }
    }
}
            

In this example:

• [FunctionName("MyTimerTrigger")] defines the name of the function.
• [TimerTrigger("0 */5 * * * *")] specifies the CRON schedule, running every 5 minutes.
• TimerInfo myTimer provides information about the timer, including whether it's past due.
• ILogger log is used for logging output.

Example: Using JavaScript (Node.js)

module.exports = async function (context, myTimer) {
    var timeStamp = new Date().toISOString();
    
    if (myTimer.isPastDue)
    {
        context.log('JavaScript isPastDue!');
    }
    context.log('JavaScript timer trigger function executed at!', timeStamp);

    // Your scheduled task logic goes here.
};
            

The function.json file for a JavaScript Timer Trigger would typically look like this:

{
  "schedule": "0 */5 * * * *",
  "bindings": [
    {
      "name": "myTimer",
      "type": "timerTrigger",
      "direction": "in",
      "schedule": "0 */5 * * * *"
    }
  ]
}
            

Managing Scheduled Tasks

Once deployed, your Timer Triggered functions will run automatically according to their schedule. You can monitor their execution through the Azure portal's monitoring features, which include logs, metrics, and execution history.

Key Considerations:

• Idempotency: Design your functions to be idempotent, meaning they can be run multiple times with the same result. This is crucial for handling retries or overlapping executions.
• Concurrency: Be aware of the default concurrency settings for your function app. For some tasks, you might want to ensure only one instance runs at a time.
• Time Zones: CRON expressions in Azure Functions are typically based on UTC. Ensure your schedule accounts for the desired time zone.
• Scalability: Azure Functions automatically scales based on demand, but long-running tasks or high-frequency schedules might require careful planning regarding resources and potential costs.

Advanced Scenarios

• Orchestrating Workflows: Combine Timer Triggers with Durable Functions to create complex, stateful scheduled workflows.
• Conditional Execution: Implement logic within your function to conditionally execute tasks based on external factors or data.
• Parameterization: Use application settings or environment variables to configure schedules dynamically.

Conclusion

Azure Functions Timer Triggers offer a robust and flexible solution for automating recurring tasks. By understanding CRON expressions and following best practices, you can effectively leverage this feature to streamline your cloud operations and build more efficient applications.