Seeking solutions to DNS resolution issues in Azure Functions

Question

Seeking solutions to DNS resolution issues in Azure Functions

Daniel 50

Hi,

We are getting frequent DNS Name resolution errors all of a sudden for our Azure Function. It will work for many hours/days and then stop working. The issue is with Azure, as we connect to the server from other sources without problems. Have tried setting custom DNS servers to 1.1.1.1 and 8.8.8.8 with no success. I have also set WEBSITE_DNS_SERVER in environment variables to the custom DNS servers, this did not help either.

The error message:

An error occurred while processing the request. Error: HTTPSConnectionPool(host='mail.REDACTED.com', port=443): Max retries exceeded with url: /EWS/Exchange.asmx (Caused by NameResolutionError("<urllib3.connection.HTTPSConnection object at 0x7fdd30044800>: Failed to resolve 'mail.REDACTED.com' ([Errno -3] Temporary failure in name resolution)"))

What can we do to solve this?

Ganesh Patapati 12,170 Reputation points Microsoft External Staff Moderator

2025-03-18T12:28:09.5066667+00:00
Hi Daniel

Could you please test nslookup on your source machine, send me the screenshots, and let me know if you have a private endpoint configured?

You can try forcing DNS resolution to happen more frequently or adjust the TTL for the DNS record on the authoritative DNS server, if possible. Additionally, consider setting up a more robust DNS query mechanism to handle retries or TTL expiration gracefully within your Azure Function.

Meantime,

I have initiated a private message where I would like to connect with you offline to resolve your issue.

Should there be any follow-up questions or concerns, please let us know and we shall try to address them.
LeelaRajeshSayana-MSFT 17,871 Reputation points Moderator

2025-03-24T21:26:15.3333333+00:00

@Daniel I am following up to see if you are still encountering this issue. Could you please let us know if you have set up any custom domain on the function app? If so, can you share the steps you might have followed while configuring the custom domain?
Daniel 50 Reputation points

2025-03-25T16:45:56.6666667+00:00

@LeelaRajeshSayana-MSFT we have not setup a custom domain for this function app. Yes, the issue is still occuring.
LeelaRajeshSayana-MSFT 17,871 Reputation points Moderator

2025-03-26T23:46:40.5066667+00:00

@Daniel Apologies for the delayed update on this issue. We are still investigating this issue internally. We will keep you posted once we identify a probable cause for this behavior.

1 answer

Your answer

Ganesh Patapati 12,170 Reputation points Microsoft External Staff Moderator

2025-03-18T12:28:09.5066667+00:00

Hi Daniel

Could you please test nslookup on your source machine, send me the screenshots, and let me know if you have a private endpoint configured?

You can try forcing DNS resolution to happen more frequently or adjust the TTL for the DNS record on the authoritative DNS server, if possible. Additionally, consider setting up a more robust DNS query mechanism to handle retries or TTL expiration gracefully within your Azure Function.

Meantime,

I have initiated a private message where I would like to connect with you offline to resolve your issue.

Should there be any follow-up questions or concerns, please let us know and we shall try to address them.
LeelaRajeshSayana-MSFT 17,871 Reputation points Moderator

2025-03-24T21:26:15.3333333+00:00

@Daniel I am following up to see if you are still encountering this issue. Could you please let us know if you have set up any custom domain on the function app? If so, can you share the steps you might have followed while configuring the custom domain?
Daniel 50 Reputation points

2025-03-25T16:45:56.6666667+00:00

@LeelaRajeshSayana-MSFT we have not setup a custom domain for this function app. Yes, the issue is still occuring.
LeelaRajeshSayana-MSFT 17,871 Reputation points Moderator

2025-03-26T23:46:40.5066667+00:00

@Daniel Apologies for the delayed update on this issue. We are still investigating this issue internally. We will keep you posted once we identify a probable cause for this behavior.

Answer 1

@Daniel We noticed that this problem was observed during the scale-out process of your Function App. When a new instance was added, it failed to start as expected, and shortly after, the other instances also began to fail during their operation. Following several attempts to start and allocate jobs, these instances gradually shut down.

Unfortunately, there are no logs that definitively confirm the root cause. What we can conclude is that the problem stems from the platform in some form. As a temporary work around until the team resolves this issue the suggestion is to implement the Auto-Heal option as below

To configure Auto-Heal for detecting and recovering from such random Function App offline failures, you can set up rules based on specific conditions like high memory usage, frequent crashes, or lack of activity. Here’s a basic example of how you can configure Auto-Heal:

Navigate to your App Service in the Azure portal.
Select “Diagnose and solve problems” from the left-hand menu.
Under “Diagnostic Tools,” select “Auto-Heal.”
Add a rule to monitor specific conditions (500 HTTP status codes in this case).
Set the action to “Recycle” the worker process or “Restart” the app service.

For more detailed steps, you can refer to the Auto-Heal documentation on Microsoft Learn.

Announcing the New Auto Healing Experience in App Service Diagnostics - Azure App Service

I will update this thread once the underlying issue has been fixed. I apologize for the inconvenience this issue has caused you and appreciate your patience in trying to resolve the issue.