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Timer Trigger for Azure Functions

The timer trigger is used to run a Function on a recurring schedule. It uses a cron expression or a timer interval to define the schedule.

Introduction

The timer trigger allows you to run your Azure Functions at specified intervals. This is useful for scheduled tasks, batch processing, or any scenario where you need to execute code periodically without an external HTTP request.

How it Works

The timer trigger utilizes a cron expression, a widely adopted standard for scheduling tasks. You define a schedule using a cron expression, and the timer trigger ensures your function executes when that schedule is met.

Configuration

The timer trigger is configured in the function.json file for your Azure Function. Here's an example:

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

Cron Expression Explained

The schedule property accepts a cron expression, which consists of six fields:

1. Seconds
2. Minutes
3. Hours
4. Day of Month
5. Month
6. Day of Week

For example, "0 */5 * * * *" means "run every 5 minutes".

Supported Languages

The timer trigger is supported across all major Azure Functions languages, including:

• C#
• JavaScript
• TypeScript
• Python
• Java
• PowerShell

Example Usage (JavaScript)

Here's a simple JavaScript function triggered by a timer:

module.exports = async function (context, myTimer) {
    const timeStamp = new Date().toISOString();
    if (myTimer.isPastDue) {
        context.log('JavaScript is running late!');
    }
    context.log('JavaScript timer trigger function ran at:', timeStamp);
};

Best Practices

• Idempotency: Ensure your timer-triggered functions are idempotent, meaning running them multiple times has the same effect as running them once.
• Error Handling: Implement robust error handling and logging to diagnose and resolve issues.
• Monitoring: Utilize Azure Monitor and Application Insights to track the execution of your timer functions.
• Avoid Overlapping: Be mindful of the frequency of your triggers to prevent overlapping executions if your function takes a long time to run.

Advanced Scenarios

Timer Intervals

Instead of a cron expression, you can specify a fixed interval:

{
  "schedule": "00:00:05",
  "bindings": [
    {
      "name": "myTimer",
      "type": "timerTrigger",
      "direction": "in",
      "schedule": "00:00:05"
    }
  ]
}

This example triggers the function every 5 seconds.

Using Function Timer Context

The timer trigger binding passes a context object to your function, which includes information like isPastDue. This property is true if the function execution was missed due to being offline or other scheduling conflicts.

Scaling

In a Consumption plan, timer triggers execute on a single instance. For scenarios requiring high throughput or guaranteed execution, consider using a Premium or App Service plan.