Azure Function Timer Trigger in Depth with Examples

Azure Functions provide a serverless compute experience that allows you to run small pieces of code, or "functions", in response to events or on a schedule.

A Timer Trigger in Azure Functions is a type of trigger that allows you to run a function on a schedule, at a specific time or interval.

This trigger is useful for tasks that need to run at a specific time, such as sending a daily report or updating a database at midnight.

You can specify the time and interval for the trigger using a CRON expression, which is a standard way of expressing a schedule in a string format.

For example, a CRON expression of "0 0 * * * *" would run the function at midnight every day.

A TimeSpan value specifies the time interval between each function invocation, unlike a NCRONTAB expression.

The TimeSpan format is hh:mm:ss when hh is less than 24, and dd:hh:mm when the first two digits are 24 or greater.

Expressed as a string, the TimeSpan format can be as simple as "01:00:00" to trigger every hour.

The format can also be used to trigger every 25 days, as seen in the example "25:00:00:00".

You'll find the basic TimerTrigger configuration in the function.json file of the created function.

The expression "0 */5 * * * *" indicates that the function will run every 5 minutes.

Here are some common TimeSpan formats:

To configure an Azure Function Timer Trigger, you'll need to edit the function.json file.

The function.json file contains the basic TimerTrigger configuration, including the expression that determines how often the function runs.

The expression 0 */5 * * * * indicates that the function will run every 5 minutes.

You can set up a TimerTrigger in an Azure Functions project configured for TypeScript by following the basic steps outlined in the setup process.

To get started with setting up a TimerTrigger, you need to have an Azure Functions project configured for TypeScript.

Broaden your view: Azure Function Local Settings Json

Error handling is crucial in Azure Function Timer Triggers, as it ensures that your function can recover from unexpected errors and continue running smoothly.

A good practice is to use try-catch blocks to catch and handle exceptions, as seen in the example of the Timer Trigger function that runs a script to update a database. This approach helps prevent the function from crashing and allows it to continue executing.

In Azure Functions, you can also configure retries for your timer triggers. This means that if a function fails, it will automatically retry the execution after a specified time interval, as demonstrated in the example of a timer trigger with a retry policy.

A fresh viewpoint: Azure Function Trigger

The timer trigger doesn't retry after a function fails. It only calls the function again at the next scheduled time.

Unlike the queue trigger, the timer trigger doesn't have a retry mechanism in place. This means that if your function fails, it will simply wait until the next scheduled time to try again.

If your function fails, it won't be called again until the next time on the schedule. This can be a good thing, as it prevents your function from getting stuck in an infinite loop of retries.

The lack of retries can actually be beneficial, as it helps prevent unnecessary workload on your system.

When troubleshooting issues with timer triggers, it's essential to know where to look for help. For information about what to do when the timer trigger doesn't work as expected, see Investigating and reporting issues with timer triggered functions not firing.

If you're experiencing issues with timer triggers, don't panic. Simply refer to the relevant section for guidance on how to proceed.

To resolve the issue, you'll need to investigate and report the problem. See Investigating and reporting issues with timer triggered functions not firing for more information.

The key to resolving the issue lies in understanding the root cause of the problem. By doing so, you'll be able to take the necessary steps to fix the issue and get your timer trigger working as expected.

Manually invoking an Azure Function timer trigger can be a game-changer for your development workflow.

You can manually invoke a timer trigger using an HTTP webhook, which is extremely useful in various scenarios.

Integration testing is one of the main benefits of manually invoking a timer trigger. This allows you to test your function in isolation, ensuring it's working as expected.

Here are some specific use cases for manually invoking a timer trigger:

Manually invoking a timer trigger can also be used to populate a cache or lookup table in a database during the initial deployment of a function. This ensures your function has the necessary data to operate efficiently.

To create the Azure Function, you'll need to create a new Azure Functions project. This can be done in VSCode by opening the command palette and typing in “Azure Functions: Create New Project”. This will guide you through the process of creating a new project.

Related reading: Create Sample Azure Function for .net Frame Work

Select an empty folder in which you want to create the project, and then select a language, such as Python, for this article. You can choose any language of your choice.

The next step is to select the Timer Trigger template for your project. This will create the default timer trigger template along with the required files.

In the function.json file of the created function, you'll find the basic TimerTrigger configuration, which includes the expression 0 */5 * * * *. This indicates that the function will run every 5 minutes.

Once you have written the function code, you can deploy it to Azure by right-clicking on the project in the Explorer pane and selecting “Deploy to Function App”. This will guide you through the process of creating a new Function App in Azure and deploying your function to it.

The TimerTrigger is a type of trigger that allows you to execute functions at regular intervals or specific times. It’s ideal for tasks that need to be executed periodically, like data cleaning, sending reports, or cache updates.

For more insights, see: Azure Logic App Blob Storage Trigger

Azure Function timer triggers can be configured to run at specific intervals, such as every 5 minutes or every hour, allowing for flexible scheduling.

For example, a timer trigger can be set to run every 5 minutes to check for new data in a database, while another timer trigger can be set to run every hour to send a daily report.

Timer triggers can be configured to run at specific times of day, such as 8am or 12pm, allowing for more precise control over when the function runs.

For instance, a timer trigger can be set to run at 8am every Monday, Wednesday, and Friday to perform a weekly task.

Timer triggers can be used to create complex scheduling scenarios, such as running a function every 15 minutes on weekdays but only every 30 minutes on weekends.

This allows for a high degree of flexibility and customization, making timer triggers a powerful tool for automating tasks and workflows.

Time zone settings for Azure Functions timer triggers can be a bit tricky, but don't worry, I've got you covered. To have your timer trigger fire at a specific time in a non-UTC time zone, you need to create an app setting named WEBSITE_TIME_ZONE.

The value of this setting depends on the operating system and plan on which your function app runs. Here's a quick rundown of the values you need to set:

Keep in mind that WEBSITE_TIME_ZONE and TZ are not supported when running on Linux in a Consumption plan.

Ncrontab Expressions are used in Azure Functions to schedule tasks with precision. They are similar to CRON expressions but include an additional sixth field for time precision in seconds.

The Ncrontab expression format is: {second} {minute} {hour} {day} {month} {day-of-week}. Each field can have a specific value, all values (*), a range (- operator), a set of values (, operator), or an interval value (/ operator).

A specific value is used to trigger a task once every hour at a specific minute, like 0 5 * * * *.

All values (*) are used to trigger a task at every minute in an hour, during a specific hour, like 0 * 5 * * *.

The - operator is used to specify a range of values, like 5-7 * * * * *.

The , operator is used to specify a set of values, like 5,8,10 * * * * *.

The / operator is used to specify an interval value, like 0 */5 * * * *.

You can use numeric values, names, or abbreviations of names to specify months or days. For days, the numeric values are 0 to 6, where 0 starts with Sunday.

Here's a summary of the types of values you can use in each field:

The default time zone used with NCRONTAB expressions is Coordinated Universal Time (UTC).

To have your CRON expression based on another time zone, create an app setting for your function app named WEBSITE_TIME_ZONE. This setting depends on the operating system and plan on which your function app runs.

Here's a breakdown of the values you can use for WEBSITE_TIME_ZONE:

Note that WEBSITE_TIME_ZONE and TZ are not currently supported when running on Linux in a Consumption plan.

Time Span is a key concept in scheduling, and it's essential to understand how it works. A TimeSpan value specifies the time interval between each function invocation.

Unlike a traditional scheduling method, a TimeSpan value doesn't specify a fixed time of day or date. Instead, it determines how often a function should be invoked. For example, a TimeSpan value of "01:00:00" means a function will be invoked every hour.

Here are some examples of TimeSpan values and what they trigger:

The format of a TimeSpan value is either hh:mm:ss or dd:hh:mm, depending on the first two digits. If the first two digits are less than 24, the format is hh:mm:ss. If the first two digits are 24 or greater, the format is dd:hh:mm.