Timer Trigger

The timer trigger in Azure Functions allows you to run a function on a schedule. This is ideal for tasks like background processing, batch jobs, or simply executing code at regular intervals.

Cron Expressions

The timer trigger uses cron expressions to define the schedule. A cron expression consists of six required fields, separated by spaces, in the following order:

{second} {minute} {hour} {day} {month} {day-of-week}

Each field can contain numbers, wildcards (*), ranges (-), lists (,), and step values (/).

Cron Field Details

Cron Expression Examples

• 0 * * * * * - Every minute
• 0 0 * * * * - Every hour at the start of the hour
• 0 0 12 * * * - Every day at noon
• 0 0 12 1 * * - On the 1st of every month at noon
• 0 15 10 * * 1-5 - Every weekday (Monday to Friday) at 10:15 AM

Configuring the Timer Trigger

The timer trigger is configured in the function.json file (for JavaScript, Python, etc.) or via attributes/decorators (for C#, Java).

function.json Example

For JavaScript or other languages using function.json, the configuration looks like this:

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

In this example:

• name: The name of the timer object in your function code.
• type: Set to timerTrigger.
• direction: Set to in as it's an input trigger.
• schedule: The cron expression defining when the function should run. In this case, "0 */5 * * * *" means every 5 minutes.

C# Attributes Configuration

For C#, you use attributes:

using Microsoft.Azure.WebJobs;

public static class TimerTriggerExample
{
    [FunctionName("TimerTriggerCSharp")]
    public static void Run([TimerTrigger("0 */5 * * * *")]TimerInfo myTimer, ILogger log)
    {
        log.LogInformation($"C# Timer trigger function executed at: {DateTime.Now}");
    }
}

The string passed to TimerTrigger is the cron expression.

TimerInfo Object

When the timer trigger fires, it passes a TimerInfo object to your function. This object provides useful information about the timer.

Common properties include:

• IsPastDue: A boolean indicating if the timer job is running late (i.e., the scheduled time has passed).
• NextDeliveryUtc: The UTC date and time when the timer is scheduled to run next.
• LastDeliveryUtc: The UTC date and time when the timer last ran.

Handling Past Due Executions

It's often a good practice to check IsPastDue and handle it appropriately. For example, you might want to skip execution if it's significantly late to avoid processing old data.

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);
    context.log('Next timer fire is at: ', myTimer.next);
};

Advanced Scheduling

Using the Lease Mechanism

Azure Functions employs a lease mechanism to ensure that only one instance of a timer-triggered function runs at a time, even in scaled-out environments. This prevents duplicate executions. You don't typically need to configure this explicitly, as it's handled by the Functions runtime.

Non-Cron Schedules (e.g., C#)

Some languages, like C#, offer alternative ways to specify schedules. For example, you can use the ScheduleStatus property to define schedules based on intervals:

using Microsoft.Azure.WebJobs;
using System;

public static class IntervalTimer
{
    [FunctionName("IntervalTimerCSharp")]
    public static void Run([TimerTrigger("00:01:00")]TimerInfo myTimer, ILogger log)
    {
        log.LogInformation($"C# Timer trigger function executed at: {DateTime.Now}");
    }
}

This example runs every 1 minute. The format is typically HH:MM:SS.

Common Use Cases

• Scheduled data ingestion or ETL processes.
• Regularly cleaning up temporary files or database entries.
• Sending out scheduled reports or notifications.
• Heartbeat checks or monitoring tasks.
• Synchronizing data between services.