AZ Functions Timer Trigger and Scheduling

The Timer trigger runs an Azure Function on a fixed schedule — like a digital alarm clock that wakes the function at a specific time or interval. No one needs to call the function manually. Azure starts it automatically based on the schedule defined in the configuration.

Timer Trigger Concept – Analogy

┌──────────────────────────────────────────────────────────────┐
│                  TIMER TRIGGER ANALOGY                       │
│                                                              │
│   Traditional Alarm Clock:                                   │
│   Set time → Clock reaches that time → Alarm rings           │
│                                                              │
│   Azure Timer Trigger:                                       │
│   Set CRON schedule → Azure reaches that time → Function runs│
│                                                              │
│   No one presses a button. No HTTP call. No manual action.   │
│   Azure fires the function automatically.                    │
└──────────────────────────────────────────────────────────────┘

Common Use Cases

• Send a daily summary email every morning at 8:00 AM
• Clean up expired records in a database every Sunday at midnight
• Sync data between two systems every 15 minutes
• Generate monthly invoices on the first day of each month
• Check a third-party API for updates every 5 minutes

Timer Trigger Configuration

function.json

{
  "bindings": [
    {
      "type": "timerTrigger",
      "direction": "in",
      "name": "myTimer",
      "schedule": "0 0 8 * * *"
    }
  ]
}

Key Properties

CRON Expression Deep Dive

Azure Functions uses a 6-field CRON expression. Each field controls a time unit:

Position:  1        2       3     4          5       6
           │        │       │     │          │       │
           ▼        ▼       ▼     ▼          ▼       ▼
Format:  {second} {minute} {hour} {day/month} {month} {day/week}

Range:     0-59    0-59    0-23    1-31       1-12    0-6
                                                      (0=Sunday)

Special Characters in CRON

Practical CRON Examples

Timer Trigger Function Code

index.js

module.exports = async function (context, myTimer) {

    // Check if the timer fired late (past the scheduled time)
    if (myTimer.isPastDue) {
        context.log("Timer is running late!");
    }

    // Log the current time
    const now = new Date().toISOString();
    context.log(`Daily report function ran at: ${now}`);

    // Place business logic here
    // Example: Send email, query database, clean up records
    await sendDailyReport();
};

async function sendDailyReport() {
    // Simulate sending a report
    console.log("Daily report sent successfully.");
}

The TimerInfo Object

The timer trigger passes a TimerInfo object into the function. This object provides information about the schedule run.

Time Zones for Timer Triggers

By default, timer triggers use UTC time. This is important because 9:00 AM UTC is different from 9:00 AM IST (India Standard Time, UTC+5:30).

To use a specific time zone, add the WEBSITE_TIME_ZONE setting to the function app's Application Settings:

Key:   WEBSITE_TIME_ZONE
Value: India Standard Time

With this setting, the CRON expression 0 0 9 * * * runs at 9:00 AM IST instead of 9:00 AM UTC.

Common Time Zone Values

Practical Example – Weekly Database Cleanup

// Runs every Sunday at 1:00 AM
// CRON: "0 0 1 * * 0"

module.exports = async function (context, myTimer) {

    context.log("Weekly cleanup started...");

    // Simulate deleting records older than 90 days
    const deletedCount = await deleteOldRecords(90);

    context.log(`Cleanup complete. Deleted ${deletedCount} old records.`);
};

async function deleteOldRecords(daysOld) {
    // In real code: connect to database and delete old records
    return 42; // Simulate 42 records deleted
}

runOnStartup – Useful During Development

Adding "runOnStartup": true to function.json makes the timer function run immediately when the app starts. This is helpful during development to test the logic without waiting for the schedule to fire.

{
  "bindings": [
    {
      "type": "timerTrigger",
      "direction": "in",
      "name": "myTimer",
      "schedule": "0 0 8 * * *",
      "runOnStartup": true
    }
  ]
}

Important: Remove or set runOnStartup to false before deploying to production. Otherwise the function runs on every app restart, which may cause unintended side effects.

Timer Trigger Flow Summary

┌──────────────────────────────────────────────────────────────┐
│                TIMER TRIGGER FLOW                            │
│                                                              │
│  Azure Internal Scheduler                                    │
│       │                                                      │
│       │  Checks: Is it time to run? (matches CRON schedule)  │
│       │                                                      │
│       ├── Not yet → Keep waiting                             │
│       │                                                      │
│       └── Yes → Fire the timer trigger                       │
│                      │                                       │
│                      ▼                                       │
│              Function code runs                              │
│                      │                                       │
│                      ▼                                       │
│              Function completes → Sleep until next run       │
└──────────────────────────────────────────────────────────────┘