Blazor Web App SqlException: Login failed for user When deployed to Azure

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Blazor Web App SqlException: Login failed for user When deployed to Azure

Braden Bowie 40

Hi,

I have a .Net 8 Blazor Web App, for some reason whenever I deploy the web app to an Azure Web app I get the following error SqlException: Login failed for user 'dummyUser'.

The issue is intermittent, it usually occurs for the first 5 or so min after publishing, then goes away for a bit. But then the error will pop up randomly at different times.

I tried the same app settings locally and there is never an issue. Further I found that TrustServerCertificate=True will prevent the error from occurring but I want this to be false for greater security.

Both the database and web app is hosted in azure, does anyone know what could be causing this?

It seems to occur most often when multiple db requests are sent at once, but sometimes even if only one.

Thanks

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Answer 1

Pradeep M 8,585 Microsoft External Staff Moderator

Hi Braden Bowie,

Thank you for reaching out to Microsoft Q & A forum.

The intermittent SqlException: Login failed for user 'dummyUser' issue after deploying your .NET 8 Blazor Web App to Azure may be occurring due to a few common reasons:

1.App Initialization Timing: Right after deployment, the application settings may not be fully loaded, which can lead to login failures. Implementing retry logic (such as using Polly) can help handle these temporary issues.

2.Connection String Settings: Please ensure the connection string configured in your Azure App Service is correct and consistent with what works locally. If possible, using Managed Identity is a more secure and reliable option than hardcoding credentials.

3.TrustServerCertificate=False: When this is set, the application requires a valid, trusted SSL certificate. Ensure that your Azure environment is able to validate the SQL server's certificate. As a temporary workaround, TrustServerCertificate=True can help, but it is less secure.

4.High Load or Concurrent Requests: If the error appears during multiple simultaneous database requests, it may be related to connection pooling or DbContext usage. Please ensure that DbContext is registered with a Scoped lifetime in your Blazor Server app.

Lastly, enabling Application Insights or Azure diagnostic logging can provide more clarity on when and why the failures occur.

If you have found the answer provided to be helpful, please click on the "Accept answer/Upvote" button so that it is useful for other members in the Microsoft Q&A community.

Braden Bowie 40 Reputation points

2025-05-06T06:34:44.0333333+00:00

I think it might be 4, but I am using a DbContext Factories as different blazor components are accessing the db at the same time. How can I prevent even if I have db factory. Turn off pooling?
Pradeep M 8,585 Reputation points Microsoft External Staff Moderator

2025-05-07T04:25:02.8466667+00:00

Hi Braden Bowie,

Using DbContextFactory is an appropriate choice for managing concurrent database access in Blazor Server applications. However, it’s important to ensure that each DbContext instance is properly created and disposed of using a using statement. Disabling connection pooling is not recommended; instead, consider increasing the Max Pool Size in your connection string to handle higher demand. Also, avoid retaining DbContext instances longer than necessary or sharing them across component lifecycles. Implementing retry logic (such as with Polly) and enabling Application Insights can help monitor and resolve transient connection issues effectively.
Braden Bowie 40 Reputation points

2025-05-08T03:13:30.29+00:00

Hi Pradeep,Thank you for the advice. I found the root cause of the issue. It appears the azure sql server firewall was preventing the app from connecting sometimes.

I have "Allow Azure Services and Resources to access this server" turned on, however it seems that the web app is not authenticated for the first few minutes since publish. Further if too many requests are sent at once it appears that some requests are not authenticated either.

For now I have whitelisted the web app IP and it works perfectly. I would like to find a slightly better solution if possible. I will continue to look. If you have any advice please let me know.

Thanks,

Braden
Pradeep M 8,585 Reputation points Microsoft External Staff Moderator

2025-05-08T04:14:44.2466667+00:00

Well done on identifying the root cause. This behavior can occur due to dynamic outbound IPs used by Azure Web Apps, particularly just after deployment. For a more stable and secure setup, consider integrating your Web App with a Virtual Network and using a Private Endpoint for Azure SQL, or configure a static outbound IP using a NAT Gateway. Additionally, using Managed Identity for database authentication eliminates the need for IP whitelisting and enhances security. While your current workaround is effective, these approaches provide greater long-term reliability and security.

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Blazor Web App SqlException: Login failed for user When deployed to Azure

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