Why my functions will be triggered every time I do the deployment

Question

Why my functions will be triggered every time I do the deployment

Zhuo Chen 20 Microsoft Employee

Why my functions will be triggered every time I do the deployment. they are timer triggered, I set the cron to trigger one time one day.

Here is one example:

[DisableFunction(FunctionAppSettings.DisableFunction)]
        [Function("TESTFunction")]
        public async Task TestFunction(
            [TimerTrigger("0 5 8 * * *")] TimerInfo myTimer)
        {

Loknathsatyasaivarma Mahali 2,470 Reputation points Microsoft External Staff Moderator

2025-06-05T04:37:46.22+00:00

Hello Zhuo Chen,

Thanks for reaching out, your timer-triggered Azure Function likely runs immediately after deployment due to the runtime's behavior of executing missed schedule occurrences. When your Function App is redeployed, it goes temporarily offline. If a scheduled execution time (e.g., 8:05 AM daily, based on your 0 5 8 * * * CRON expression) occurs during this downtime, the Azure Functions runtime detects the missed schedule once the app restarts and immediately invokes the function to catch up.

As stated in the official Microsoft documentation:

“When the runtime becomes active again, it will detect any missed schedule occurrences ... and run the function immediately.” Azure Timer Trigger Docs

You can confirm this behavior using the TimerInfo.IsPastDue property inside your function — it will be true during such catch-up executions.

Although the RunOnStartup property (which defaults to false) can also cause immediate invocation if set to true, in your case, the catch-up logic due to missed triggers during deployment is the more likely cause.
Zhuo Chen 20 Reputation points Microsoft Employee

2025-06-05T05:36:57.4066667+00:00

Thank you. But I encountered a situation where I found two runs on the day of deployment. There was no missing run, but just an extra run. What should I do? Thanks!
Loknathsatyasaivarma Mahali 2,470 Reputation points Microsoft External Staff Moderator

2025-06-05T07:37:57.5166667+00:00
Hello Zhuo Chen,

If you're seeing two runs on the day of deployment when no schedule was missed, the primary suspect is the RunOnStartup property. If your function is defined like [TimerTrigger("...", RunOnStartup = true)], it will execute immediately whenever the runtime starts (such as after a deployment), in addition to its scheduled run. To prevent this, ensure that RunOnStartup is set to false or omitted (as it defaults to false).

If RunOnStartup is already set to false, the extra run might still be due to the runtime detecting a catch-up for a less obvious missed schedule (possibly from before deployment). To investigate, enhance your logging to include TimerInfo.IsPastDue and TimerInfo.ScheduleStatus (which shows the last and next scheduled run times). After your next deployment, check the Azure portal's Monitor tab:

If one invocation shows IsPastDue: true, it was a catch-up.

The other should align with your normal schedule.

Also, confirm that your WEBSITE_TIME_ZONE app setting is correctly configured to avoid any time zone-based misinterpretation of the CRON schedule.
Loknathsatyasaivarma Mahali 2,470 Reputation points Microsoft External Staff Moderator

2025-06-09T01:14:59.89+00:00

Hello Zhuo Chen,Just checking into see if the above provided information helps you in better understanding if you have any further concerns, please feel free to drop them here.
Loknathsatyasaivarma Mahali 2,470 Reputation points Microsoft External Staff Moderator

2025-06-10T01:03:09.93+00:00

Hello Zhuo Chen,

We wanted to follow up on the issue you encountered. Please let us know if it's resolved or if you need further assistance.
Pravallika Kothaveeranna Gari 955 Reputation points Microsoft External Staff Moderator

2025-06-12T16:26:30.8033333+00:00
Hi Zhuo Chen,

How are you deploying the function to Azure?

Check the logs or blobs in the storage account linked to your function App and look for:

Timer state blobs under azure-webjobs-hosts/timers/

Any logs indicating "missed schedule run" or "executing past due".
Pravallika Kothaveeranna Gari 955 Reputation points Microsoft External Staff Moderator

2025-06-13T11:39:27.45+00:00

Hello Zhuo Chen, Just checking into see if the above provided information helps you to figure out the root cause. Additionally, if you have any further queries, please feel free to post back.
Zhuo Chen 20 Reputation points Microsoft Employee

2025-06-18T02:53:22.0933333+00:00

we deploy the function app using arm template through ev2.

Your answer

Loknathsatyasaivarma Mahali 2,470 Reputation points Microsoft External Staff Moderator

2025-06-05T04:37:46.22+00:00

Hello Zhuo Chen,

Thanks for reaching out, your timer-triggered Azure Function likely runs immediately after deployment due to the runtime's behavior of executing missed schedule occurrences. When your Function App is redeployed, it goes temporarily offline. If a scheduled execution time (e.g., 8:05 AM daily, based on your 0 5 8 * * * CRON expression) occurs during this downtime, the Azure Functions runtime detects the missed schedule once the app restarts and immediately invokes the function to catch up.

As stated in the official Microsoft documentation:

“When the runtime becomes active again, it will detect any missed schedule occurrences ... and run the function immediately.” Azure Timer Trigger Docs

You can confirm this behavior using the TimerInfo.IsPastDue property inside your function — it will be true during such catch-up executions.

Although the RunOnStartup property (which defaults to false) can also cause immediate invocation if set to true, in your case, the catch-up logic due to missed triggers during deployment is the more likely cause.
Zhuo Chen 20 Reputation points Microsoft Employee

2025-06-05T05:36:57.4066667+00:00

Thank you. But I encountered a situation where I found two runs on the day of deployment. There was no missing run, but just an extra run. What should I do? Thanks!
Loknathsatyasaivarma Mahali 2,470 Reputation points Microsoft External Staff Moderator

2025-06-05T07:37:57.5166667+00:00

Hello Zhuo Chen,

If you're seeing two runs on the day of deployment when no schedule was missed, the primary suspect is the RunOnStartup property. If your function is defined like [TimerTrigger("...", RunOnStartup = true)], it will execute immediately whenever the runtime starts (such as after a deployment), in addition to its scheduled run. To prevent this, ensure that RunOnStartup is set to false or omitted (as it defaults to false).

If RunOnStartup is already set to false, the extra run might still be due to the runtime detecting a catch-up for a less obvious missed schedule (possibly from before deployment). To investigate, enhance your logging to include TimerInfo.IsPastDue and TimerInfo.ScheduleStatus (which shows the last and next scheduled run times). After your next deployment, check the Azure portal's Monitor tab:

If one invocation shows IsPastDue: true, it was a catch-up.

The other should align with your normal schedule.

Also, confirm that your WEBSITE_TIME_ZONE app setting is correctly configured to avoid any time zone-based misinterpretation of the CRON schedule.
Loknathsatyasaivarma Mahali 2,470 Reputation points Microsoft External Staff Moderator

2025-06-09T01:14:59.89+00:00

Hello Zhuo Chen,Just checking into see if the above provided information helps you in better understanding if you have any further concerns, please feel free to drop them here.
Loknathsatyasaivarma Mahali 2,470 Reputation points Microsoft External Staff Moderator

2025-06-10T01:03:09.93+00:00

Hello Zhuo Chen,

We wanted to follow up on the issue you encountered. Please let us know if it's resolved or if you need further assistance.
Pravallika Kothaveeranna Gari 955 Reputation points Microsoft External Staff Moderator

2025-06-12T16:26:30.8033333+00:00

Hi Zhuo Chen,

How are you deploying the function to Azure?

Check the logs or blobs in the storage account linked to your function App and look for:

Timer state blobs under azure-webjobs-hosts/timers/

Any logs indicating "missed schedule run" or "executing past due".
Pravallika Kothaveeranna Gari 955 Reputation points Microsoft External Staff Moderator

2025-06-13T11:39:27.45+00:00

Hello Zhuo Chen, Just checking into see if the above provided information helps you to figure out the root cause. Additionally, if you have any further queries, please feel free to post back.
Zhuo Chen 20 Reputation points Microsoft Employee

2025-06-18T02:53:22.0933333+00:00

we deploy the function app using arm template through ev2.

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Why my functions will be triggered every time I do the deployment

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