Having issues with Azure Function App, which gives error if not run for a week

Question

I have a azure function app.

This function is executed when a azure app service makes a request.

The azure function gets file from azure storage for processing.

If the request is not made for a week, the function app gives error

Object reference not set to an instance of an object

When I republish my azure function without making any code change, the function runs fine.

Answer 1

Hello @Tasneem Nomani

Welcome to Microsoft QnA!

What type of Azure Functions are you using ?

I can think a lot of issues causing this

Most probale

1. Cold Start Issues:

• Explanation: Azure Functions can experience "cold starts" when they haven't been used for a while. This means the runtime environment needs to be spun up, which can take some time. During a cold start, dependencies might not be fully initialized, leading to null reference errors.
• Mitigation:
  • Warm-up Triggers: Implement a recurring timer trigger or a scheduled HTTP ping to keep your function warm and prevent cold starts.
    • Premium Plan: Consider using the Azure Functions Premium plan, which offers features like pre-warmed instances to minimize cold start latency.

2. Dependency Injection Problems:

• Explanation: If your function relies on dependency injection to access external services (like Azure Storage), the connection might not be established or might time out after a period of inactivity.
• Mitigation:
  • Retry Logic: Add retry logic around your dependency injection calls to handle transient connection failures.
  • Singleton Services: If appropriate, configure your dependencies as singletons to maintain the connection across function executions.
• https://github.com/Azure/azure-functions-host/issues/8021#issuecomment-1004303750

https://learn.microsoft.com/en-us/answers/questions/1409596/always-on-in-azure-function-apps-running-on-an-app

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I hope this helps!

Kindly mark the answer as Accepted and Upvote in case it helped!

Regards

Answer 2

Hello Tasneem Nomani,

Thanks for your question.

This is most likely as a result of cold start. When your function isn't invoked for an extended period resources are usually deallocated. So the first request usually takes longer while re-allocating.

See: https://azure.microsoft.com/en-us/blog/understanding-serverless-cold-start/

You can mark it 'Accept Answer' and 'Upvote' if this helped you

Regards,

Abiola

Answer 3

Thank you for the response.

I have implemented lazy loading of services in startup.cs.

I also created a timer trigger function to keep accessing the function every hour.

Hopefully this will resolve my issue.

Answer 4

The azure web app that is calling the function is also facing same issue.

asp.net mvc web application hosted as azure app service, this uses forms authentication

I can login to the site and browse.

When I try to submit a form on the site it gives error

"Error An error occurred while processing your request"

Without making any changes to the code, if i republish the code to azure or restart the app service, the error is gone.

I looked at the application event log in azure portal.

it has this error 4005 Forms authentication failed for the request. Reason: The ticket supplied has expired.

Answer 5

Hello @Tasneem Nomani

We have to enable more logging to see deeper

Can you do that ?

Also enable Application Insights probably we will get something for both apps

In the Web App also enable:

I hope this helps!

Kindly mark the answer as Accepted and Upvote in case it helped!

Regards