Azure Functions: Timer Trigger Tutorial

This tutorial guides you through creating and configuring a Timer Trigger for Azure Functions, enabling your functions to run on a scheduled basis.

What is a Timer Trigger?

A Timer Trigger allows you to execute your Azure Functions code at regular intervals. This is incredibly useful for tasks like:

• Running background jobs
• Processing data periodically
• Sending out scheduled reports
• Orchestrating workflows

Prerequisites

• Azure Subscription: If you don't have one, sign up for a free account.
• Azure Functions Core Tools installed.
• An IDE like Visual Studio Code with the Azure Functions extension.

Step 1: Create a New Azure Functions Project

Open Visual Studio Code, navigate to the Azure extension, and select "Create New Project...". Choose a folder for your project, select "Azure Functions" as the project type, and then choose your preferred language (e.g., C#, JavaScript, Python). For this example, we'll use JavaScript.

Step 2: Add a Timer Trigger

Once your project is created, you can add a new function. In VS Code, go to the Azure extension, right-click on your project folder, and select "Add Azure Function...". Choose "Timer trigger" as the function type. You'll be prompted to name your function (e.g., TimerTriggerJS) and set the schedule.

Configuring the Schedule

The schedule is defined using a CRON expression. A common example is 0 */5 * * * *, which means "run every 5 minutes".

0 */5 * * * *

You can use various tools online to help you generate CRON expressions (e.g., crontab.guru).

Step 3: Understanding the Timer Trigger Code

A typical Timer Trigger function (in JavaScript) will look something like this:

// index.js
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!', timeStamp);
};
        

And the configuration file (function.json):

{
  "schedule": "0 */5 * * * *",
  "bindings": [
    {
      "name": "myTimer",
      "type": "timerTrigger",
      "direction": "in",
      "schedule": "0 */5 * * * *"
    },
    {
      "name": "outputBlob",
      "type": "blob",
      "path": "mycontainer/{name}.txt",
      "direction": "out"
    }
  ]
}
        

Notice how the schedule property in function.json defines when the function runs. The myTimer object passed into the function contains information like whether it's running late.

Step 4: Running Locally

To test your Timer Trigger locally, open a terminal in your project's root directory and run:

The Azure Functions Host will start, and your timer function will begin executing according to its schedule. You'll see the log messages in the terminal.

Step 5: Deploying to Azure

Once you're satisfied with your local testing, you can deploy your function app to Azure:

Ensure your CRON schedule in function.json is correctly set for production use. You can also modify the schedule directly in the Azure portal after deployment.

Managing and Monitoring

After deployment, you can monitor your Timer Trigger's executions and manage its schedule through the Azure portal:

• Navigate to your Function App in the Azure portal.
• Select your Timer Trigger function.
• Check the "Monitor" tab for execution logs and history.
• Go to the "Overview" page, and click "Get Function URL" (though this is not typically used for Timer Triggers directly).
• Under "Platform features", you can find "Function runtime settings" where the CRON expression can be edited directly.

Troubleshooting Tips

• Incorrect CRON Expression: Double-check your CRON syntax. Use tools like crontab.guru for validation.
• Timezone Issues: CRON schedules are based on UTC by default. If you need a different timezone, ensure your expression reflects that or handle timezone conversions within your function logic.
• Function Host Not Running: Verify that func start is running locally or that the Function App is running correctly in Azure.
• Scale Issues: For very frequent triggers, consider the consumption plan's limitations or choose a different hosting plan if necessary.